/**************************************************************************** ** ** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies). ** All rights reserved. ** Contact: Nokia Corporation (qt-info@nokia.com) ** ** This file is part of the QtGui module of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:LGPL$ ** GNU Lesser General Public License Usage ** This file may be used under the terms of the GNU Lesser General Public ** License version 2.1 as published by the Free Software Foundation and ** appearing in the file LICENSE.LGPL included in the packaging of this ** file. Please review the following information to ensure the GNU Lesser ** General Public License version 2.1 requirements will be met: ** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. ** ** In addition, as a special exception, Nokia gives you certain additional ** rights. These rights are described in the Nokia Qt LGPL Exception ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. ** ** GNU General Public License Usage ** Alternatively, this file may be used under the terms of the GNU General ** Public License version 3.0 as published by the Free Software Foundation ** and appearing in the file LICENSE.GPL included in the packaging of this ** file. Please review the following information to ensure the GNU General ** Public License version 3.0 requirements will be met: ** http://www.gnu.org/copyleft/gpl.html. ** ** Other Usage ** Alternatively, this file may be used in accordance with the terms and ** conditions contained in a signed written agreement between you and Nokia. ** ** ** ** ** ** $QT_END_LICENSE$ ** ****************************************************************************/ #include "qkbd_qws.h" #include "qkbd_qws_p.h" #ifndef QT_NO_QWS_KEYBOARD #include #include #include #ifdef Q_WS_QWS #include "qwindowsystem_qws.h" #include "qscreen_qws.h" #endif #ifdef Q_WS_QPA #include #include #endif #include "qtimer.h" #include //#define QT_DEBUG_KEYMAP QT_BEGIN_NAMESPACE class QWSKbPrivate : public QObject { Q_OBJECT public: QWSKbPrivate(QWSKeyboardHandler *h, const QString &device) : m_handler(h), m_modifiers(0), m_composing(0), m_dead_unicode(0xffff), m_no_zap(false), m_do_compose(false), m_keymap(0), m_keymap_size(0), m_keycompose(0), m_keycompose_size(0) { m_ar_timer = new QTimer(this); m_ar_timer->setSingleShot(true); connect(m_ar_timer, SIGNAL(timeout()), SLOT(autoRepeat())); m_ar_delay = 400; m_ar_period = 80; memset(m_locks, 0, sizeof(m_locks)); QString keymap; QStringList args = device.split(QLatin1Char(':')); foreach (const QString &arg, args) { if (arg.startsWith(QLatin1String("keymap="))) keymap = arg.mid(7); else if (arg == QLatin1String("disable-zap")) m_no_zap = true; else if (arg == QLatin1String("enable-compose")) m_do_compose = true; else if (arg.startsWith(QLatin1String("repeat-delay="))) m_ar_delay = arg.mid(13).toInt(); else if (arg.startsWith(QLatin1String("repeat-rate="))) m_ar_period = arg.mid(12).toInt(); } if (keymap.isEmpty() || !loadKeymap(keymap)) unloadKeymap(); } ~QWSKbPrivate() { unloadKeymap(); } void beginAutoRepeat(int uni, int code, Qt::KeyboardModifiers mod) { m_ar_unicode = uni; m_ar_keycode = code; m_ar_modifier = mod; m_ar_timer->start(m_ar_delay); } void endAutoRepeat() { m_ar_timer->stop(); } static Qt::KeyboardModifiers toQtModifiers(quint8 mod) { Qt::KeyboardModifiers qtmod = Qt::NoModifier; if (mod & (QWSKeyboard::ModShift | QWSKeyboard::ModShiftL | QWSKeyboard::ModShiftR)) qtmod |= Qt::ShiftModifier; if (mod & (QWSKeyboard::ModControl | QWSKeyboard::ModCtrlL | QWSKeyboard::ModCtrlR)) qtmod |= Qt::ControlModifier; if (mod & QWSKeyboard::ModAlt) qtmod |= Qt::AltModifier; return qtmod; } void unloadKeymap(); bool loadKeymap(const QString &file); private slots: void autoRepeat() { m_handler->processKeyEvent(m_ar_unicode, m_ar_keycode, m_ar_modifier, false, true); m_handler->processKeyEvent(m_ar_unicode, m_ar_keycode, m_ar_modifier, true, true); m_ar_timer->start(m_ar_period); } private: QWSKeyboardHandler *m_handler; // auto repeat simulation int m_ar_unicode; int m_ar_keycode; Qt::KeyboardModifiers m_ar_modifier; int m_ar_delay; int m_ar_period; QTimer *m_ar_timer; // keymap handling quint8 m_modifiers; quint8 m_locks[3]; int m_composing; quint16 m_dead_unicode; bool m_no_zap; bool m_do_compose; const QWSKeyboard::Mapping *m_keymap; int m_keymap_size; const QWSKeyboard::Composing *m_keycompose; int m_keycompose_size; static const QWSKeyboard::Mapping s_keymap_default[]; static const QWSKeyboard::Composing s_keycompose_default[]; friend class QWSKeyboardHandler; }; // simple builtin US keymap #include "qkbd_defaultmap_qws_p.h" // the unloadKeymap() function needs to be AFTER the defaultmap include, // since the sizeof(s_keymap_default) wouldn't work otherwise. void QWSKbPrivate::unloadKeymap() { if (m_keymap && m_keymap != s_keymap_default) delete [] m_keymap; if (m_keycompose && m_keycompose != s_keycompose_default) delete [] m_keycompose; m_keymap = s_keymap_default; m_keymap_size = sizeof(s_keymap_default) / sizeof(s_keymap_default[0]); m_keycompose = s_keycompose_default; m_keycompose_size = sizeof(s_keycompose_default) / sizeof(s_keycompose_default[0]); // reset state, so we could switch keymaps at runtime m_modifiers = 0; memset(m_locks, 0, sizeof(m_locks)); m_composing = 0; m_dead_unicode = 0xffff; } bool QWSKbPrivate::loadKeymap(const QString &file) { QFile f(file); if (!f.open(QIODevice::ReadOnly)) { qWarning("Could not open keymap file '%s'", qPrintable(file)); return false; } // .qmap files have a very simple structure: // quint32 magic (QWSKeyboard::FileMagic) // quint32 version (1) // quint32 keymap_size (# of struct QWSKeyboard::Mappings) // quint32 keycompose_size (# of struct QWSKeyboard::Composings) // all QWSKeyboard::Mappings via QDataStream::operator(<<|>>) // all QWSKeyboard::Composings via QDataStream::operator(<<|>>) quint32 qmap_magic, qmap_version, qmap_keymap_size, qmap_keycompose_size; QDataStream ds(&f); ds >> qmap_magic >> qmap_version >> qmap_keymap_size >> qmap_keycompose_size; if (ds.status() != QDataStream::Ok || qmap_magic != QWSKeyboard::FileMagic || qmap_version != 1 || qmap_keymap_size == 0) { qWarning("'%s' is not a valid .qmap keymap file.", qPrintable(file)); return false; } QWSKeyboard::Mapping *qmap_keymap = new QWSKeyboard::Mapping[qmap_keymap_size]; QWSKeyboard::Composing *qmap_keycompose = qmap_keycompose_size ? new QWSKeyboard::Composing[qmap_keycompose_size] : 0; for (quint32 i = 0; i < qmap_keymap_size; ++i) ds >> qmap_keymap[i]; for (quint32 i = 0; i < qmap_keycompose_size; ++i) ds >> qmap_keycompose[i]; if (ds.status() != QDataStream::Ok) { delete [] qmap_keymap; delete [] qmap_keycompose; qWarning("Keymap file '%s' can not be loaded.", qPrintable(file)); return false; } // unload currently active and clear state unloadKeymap(); m_keymap = qmap_keymap; m_keymap_size = qmap_keymap_size; m_keycompose = qmap_keycompose; m_keycompose_size = qmap_keycompose_size; m_do_compose = true; return true; } /*! \class QWSKeyboardHandler \ingroup qws \brief The QWSKeyboardHandler class is a base class for keyboard drivers in Qt for Embedded Linux. Note that this class is only available in \l{Qt for Embedded Linux}. \l{Qt for Embedded Linux} provides ready-made drivers for several keyboard protocols, see the \l{Qt for Embedded Linux Character Input}{character input} documentation for details. Custom keyboard drivers can be implemented by subclassing the QWSKeyboardHandler class and creating a keyboard driver plugin (derived from QKbdDriverPlugin). The default implementation of the QKbdDriverFactory class will automatically detect the plugin, and load the driver into the server application at run-time using Qt's \l{How to Create Qt Plugins}{plugin system}. The keyboard driver receives keyboard events from the system device and encapsulates each event with an instance of the QWSEvent class which it then passes to the server application (the server is responsible for propagating the event to the appropriate client). To receive keyboard events, a QWSKeyboardHandler object will usually create a QSocketNotifier object for the given device. The QSocketNotifier class provides support for monitoring activity on a file descriptor. When the socket notifier receives data, it will call the keyboard driver's processKeyEvent() function to send the event to the \l{Qt for Embedded Linux} server application for relaying to clients. QWSKeyboardHandler also provides functions to control auto-repetion of key sequences, beginAutoRepeat() and endAutoRepeat(), and the transformDirKey() function enabling transformation of arrow keys according to the display orientation. \sa QKbdDriverPlugin, QKbdDriverFactory, {Qt for Embedded Linux Character Input} */ /*! Constructs a keyboard driver. The \a device argument is passed by the QWS_KEYBOARD environment variable. Call the QWSServer::setKeyboardHandler() function to make the newly created keyboard driver, the primary driver. Note that the primary driver is controlled by the system, i.e., the system will delete it upon exit. */ QWSKeyboardHandler::QWSKeyboardHandler(const QString &device) { d = new QWSKbPrivate(this, device); } /*! \overload */ QWSKeyboardHandler::QWSKeyboardHandler() { d = new QWSKbPrivate(this, QString()); } /*! Destroys this keyboard driver. Do not call this function if this driver is the primary keyboard handler, i.e., if QWSServer::setKeyboardHandler() function has been called passing this driver as argument. The primary keyboard driver is deleted by the system. */ QWSKeyboardHandler::~QWSKeyboardHandler() { delete d; } /*! Sends a key event to the \l{Qt for Embedded Linux} server application. The key event is identified by its \a unicode value and the \a keycode, \a modifiers, \a isPress and \a autoRepeat parameters. The \a keycode parameter is the Qt keycode value as defined by the Qt::Key enum. The \a modifiers is an OR combination of Qt::KeyboardModifier values, indicating whether \gui Shift/Alt/Ctrl keys are pressed. The \a isPress parameter is true if the event is a key press event and \a autoRepeat is true if the event is caused by an auto-repeat mechanism and not an actual key press. Note that this function does not handle key mapping. Please use processKeycode() if you need that functionality. \sa processKeycode(), beginAutoRepeat(), endAutoRepeat(), transformDirKey() */ void QWSKeyboardHandler::processKeyEvent(int unicode, int keycode, Qt::KeyboardModifiers modifiers, bool isPress, bool autoRepeat) { #if defined(Q_WS_QWS) qwsServer->processKeyEvent(unicode, keycode, modifiers, isPress, autoRepeat); #elif defined(Q_WS_QPA) QEvent::Type type = isPress ? QEvent::KeyPress : QEvent::KeyRelease; QString str; if (unicode != 0xffff) str = QString(unicode); QWindowSystemInterface::handleKeyEvent(0, type, keycode, modifiers, str); #endif } /*! \fn int QWSKeyboardHandler::transformDirKey(int keycode) Transforms the arrow key specified by the given \a keycode, to the orientation of the display and returns the transformed keycode. The \a keycode is a Qt::Key value. The values identifying arrow keys are: \list \o Qt::Key_Left \o Qt::Key_Up \o Qt::Key_Right \o Qt::Key_Down \endlist \sa processKeyEvent() */ int QWSKeyboardHandler::transformDirKey(int key) { #ifdef Q_WS_QWS static int dir_keyrot = -1; if (dir_keyrot < 0) { // get the rotation switch (qgetenv("QWS_CURSOR_ROTATION").toInt()) { case 90: dir_keyrot = 1; break; case 180: dir_keyrot = 2; break; case 270: dir_keyrot = 3; break; default: dir_keyrot = 0; break; } } int xf = qt_screen->transformOrientation() + dir_keyrot; return (key-Qt::Key_Left+xf)%4+Qt::Key_Left; #else return 0; #endif } /*! \fn void QWSKeyboardHandler::beginAutoRepeat(int unicode, int keycode, Qt::KeyboardModifiers modifier) Begins auto-repeating the specified key press; after a short delay the key press is sent periodically until the endAutoRepeat() function is called. The key press is specified by its \a unicode, \a keycode and \a modifier state. \sa endAutoRepeat(), processKeyEvent() */ void QWSKeyboardHandler::beginAutoRepeat(int uni, int code, Qt::KeyboardModifiers mod) { d->beginAutoRepeat(uni, code, mod); } /*! Stops auto-repeating a key press. \sa beginAutoRepeat(), processKeyEvent() */ void QWSKeyboardHandler::endAutoRepeat() { d->endAutoRepeat(); } /*! \enum QWSKeyboardHandler::KeycodeAction This enum describes the various special actions that actual QWSKeyboardHandler implementations have to take care of. \value None No further action required. \value CapsLockOn Set the state of the Caps lock LED to on. \value CapsLockOff Set the state of the Caps lock LED to off. \value NumLockOn Set the state of the Num lock LED to on. \value NumLockOff Set the state of the Num lock LED to off. \value ScrollLockOn Set the state of the Scroll lock LED to on. \value ScrollLockOff Set the state of the Scroll lock LED to off. \value PreviousConsole Switch to the previous virtual console (by default Ctrl+Alt+Left on Linux). \value NextConsole Switch to the next virtual console (by default Ctrl+Alt+Right on Linux). \value SwitchConsoleFirst Switch to the first virtual console (0). \value SwitchConsoleLast Switch to the last virtual console (255). \value SwitchConsoleMask If the KeyAction value is between SwitchConsoleFirst and SwitchConsoleLast, you can use this mask to get the specific virtual console number to switch to. \value Reboot Reboot the machine - this is ignored in both the TTY and LinuxInput handlers though (by default Ctrl+Alt+Del on Linux). \sa processKeycode() */ /*! \fn QWSKeyboardHandler::KeycodeAction QWSKeyboardHandler::processKeycode(quint16 keycode, bool isPress, bool autoRepeat) \since 4.6 Maps \a keycode according to a keymap and sends that key event to the \l{Qt for Embedded Linux} server application. Please see the \l{Qt for Embedded Linux Character Input} and the \l {kmap2qmap} documentations for a description on how to create and use keymap files. The key event is identified by its \a keycode value and the \a isPress and \a autoRepeat parameters. The \a keycode parameter is \bold NOT the Qt keycode value as defined by the Qt::Key enum. This functions expects a standard Linux 16 bit kernel keycode as it is used in the Linux Input Event sub-system. This \a keycode is transformed to a Qt::Key code by using either a compiled-in US keyboard layout or by dynamically loading a keymap at startup which can be specified via the QWS_KEYBOARD environment variable. The \a isPress parameter is true if the event is a key press event and \a autoRepeat is true if the event is caused by an auto-repeat mechanism and not an actual key press. The return value indicates if the actual QWSKeyboardHandler implementation needs to take care of a special action, like console switching or LED handling. If standard Linux console keymaps are used, \a keycode must be one of the standardized values defined in \c /usr/include/linux/input.h \sa processKeyEvent(), KeycodeAction */ QWSKeyboardHandler::KeycodeAction QWSKeyboardHandler::processKeycode(quint16 keycode, bool pressed, bool autorepeat) { KeycodeAction result = None; bool first_press = pressed && !autorepeat; const QWSKeyboard::Mapping *map_plain = 0; const QWSKeyboard::Mapping *map_withmod = 0; // get a specific and plain mapping for the keycode and the current modifiers for (int i = 0; i < d->m_keymap_size && !(map_plain && map_withmod); ++i) { const QWSKeyboard::Mapping *m = d->m_keymap + i; if (m->keycode == keycode) { if (m->modifiers == 0) map_plain = m; quint8 testmods = d->m_modifiers; if (d->m_locks[0] /*CapsLock*/ && (m->flags & QWSKeyboard::IsLetter)) testmods ^= QWSKeyboard::ModShift; if (m->modifiers == testmods) map_withmod = m; } } #ifdef QT_DEBUG_KEYMAP qWarning("Processing key event: keycode=%3d, modifiers=%02x pressed=%d, autorepeat=%d | plain=%d, withmod=%d, size=%d", \ keycode, d->m_modifiers, pressed ? 1 : 0, autorepeat ? 1 : 0, \ map_plain ? map_plain - d->m_keymap : -1, \ map_withmod ? map_withmod - d->m_keymap : -1, \ d->m_keymap_size); #endif const QWSKeyboard::Mapping *it = map_withmod ? map_withmod : map_plain; if (!it) { #ifdef QT_DEBUG_KEYMAP // we couldn't even find a plain mapping qWarning("Could not find a suitable mapping for keycode: %3d, modifiers: %02x", keycode, d->m_modifiers); #endif return result; } bool skip = false; quint16 unicode = it->unicode; quint32 qtcode = it->qtcode; if ((it->flags & QWSKeyboard::IsModifier) && it->special) { // this is a modifier, i.e. Shift, Alt, ... if (pressed) d->m_modifiers |= quint8(it->special); else d->m_modifiers &= ~quint8(it->special); } else if (qtcode >= Qt::Key_CapsLock && qtcode <= Qt::Key_ScrollLock) { // (Caps|Num|Scroll)Lock if (first_press) { quint8 &lock = d->m_locks[qtcode - Qt::Key_CapsLock]; lock ^= 1; switch (qtcode) { case Qt::Key_CapsLock : result = lock ? CapsLockOn : CapsLockOff; break; case Qt::Key_NumLock : result = lock ? NumLockOn : NumLockOff; break; case Qt::Key_ScrollLock: result = lock ? ScrollLockOn : ScrollLockOff; break; default : break; } } } else if ((it->flags & QWSKeyboard::IsSystem) && it->special && first_press) { switch (it->special) { case QWSKeyboard::SystemReboot: result = Reboot; break; case QWSKeyboard::SystemZap: if (!d->m_no_zap) qApp->quit(); break; case QWSKeyboard::SystemConsolePrevious: result = PreviousConsole; break; case QWSKeyboard::SystemConsoleNext: result = NextConsole; break; default: if (it->special >= QWSKeyboard::SystemConsoleFirst && it->special <= QWSKeyboard::SystemConsoleLast) { result = KeycodeAction(SwitchConsoleFirst + ((it->special & QWSKeyboard::SystemConsoleMask) & SwitchConsoleMask)); } break; } skip = true; // no need to tell QWS about it } else if ((qtcode == Qt::Key_Multi_key) && d->m_do_compose) { // the Compose key was pressed if (first_press) d->m_composing = 2; skip = true; } else if ((it->flags & QWSKeyboard::IsDead) && d->m_do_compose) { // a Dead key was pressed if (first_press && d->m_composing == 1 && d->m_dead_unicode == unicode) { // twice d->m_composing = 0; qtcode = Qt::Key_unknown; // otherwise it would be Qt::Key_Dead... } else if (first_press && unicode != 0xffff) { d->m_dead_unicode = unicode; d->m_composing = 1; skip = true; } else { skip = true; } } if (!skip) { // a normal key was pressed const int modmask = Qt::ShiftModifier | Qt::ControlModifier | Qt::AltModifier | Qt::MetaModifier | Qt::KeypadModifier; // we couldn't find a specific mapping for the current modifiers, // or that mapping didn't have special modifiers: // so just report the plain mapping with additional modifiers. if ((it == map_plain && it != map_withmod) || (map_withmod && !(map_withmod->qtcode & modmask))) { qtcode |= QWSKbPrivate::toQtModifiers(d->m_modifiers); } if (d->m_composing == 2 && first_press && !(it->flags & QWSKeyboard::IsModifier)) { // the last key press was the Compose key if (unicode != 0xffff) { int idx = 0; // check if this code is in the compose table at all for ( ; idx < d->m_keycompose_size; ++idx) { if (d->m_keycompose[idx].first == unicode) break; } if (idx < d->m_keycompose_size) { // found it -> simulate a Dead key press d->m_dead_unicode = unicode; unicode = 0xffff; d->m_composing = 1; skip = true; } else { d->m_composing = 0; } } else { d->m_composing = 0; } } else if (d->m_composing == 1 && first_press && !(it->flags & QWSKeyboard::IsModifier)) { // the last key press was a Dead key bool valid = false; if (unicode != 0xffff) { int idx = 0; // check if this code is in the compose table at all for ( ; idx < d->m_keycompose_size; ++idx) { if (d->m_keycompose[idx].first == d->m_dead_unicode && d->m_keycompose[idx].second == unicode) break; } if (idx < d->m_keycompose_size) { quint16 composed = d->m_keycompose[idx].result; if (composed != 0xffff) { unicode = composed; qtcode = Qt::Key_unknown; valid = true; } } } if (!valid) { unicode = d->m_dead_unicode; qtcode = Qt::Key_unknown; } d->m_composing = 0; } if (!skip) { #ifdef QT_DEBUG_KEYMAP qWarning("Processing: uni=%04x, qt=%08x, qtmod=%08x", unicode, qtcode & ~modmask, (qtcode & modmask)); #endif // send the result to the QWS server processKeyEvent(unicode, qtcode & ~modmask, Qt::KeyboardModifiers(qtcode & modmask), pressed, autorepeat); } } return result; } QT_END_NAMESPACE #include "qkbd_qws.moc" #endif // QT_NO_QWS_KEYBOARD id='n94' href='#n94'>94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 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/*
 * tkImgPNG.c --
 *
 *	A Tk photo image file handler for PNG files.
 *
 * Copyright (c) 2006-2008 Muonics, Inc.
 * Copyright (c) 2008 Donal K. Fellows
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 */

#include "tkInt.h"

#define	PNG_INT32(a,b,c,d)	\
	(((long)(a) << 24) | ((long)(b) << 16) | ((long)(c) << 8) | (long)(d))
#define	PNG_BLOCK_SZ	1024		/* Process up to 1k at a time. */
#define PNG_MIN(a, b) (((a) < (b)) ? (a) : (b))

/*
 * Every PNG image starts with the following 8-byte signature.
 */

#define PNG_SIG_SZ	8
static const unsigned char pngSignature[] = {
    137, 80, 78, 71, 13, 10, 26, 10
};

static const int startLine[8] = {
    0, 0, 0, 4, 0, 2, 0, 1
};

/*
 * Chunk type flags.
 */

#define PNG_CF_ANCILLARY 0x10000000L	/* Non-critical chunk (can ignore). */
#define PNG_CF_PRIVATE   0x00100000L	/* Application-specific chunk. */
#define PNG_CF_RESERVED  0x00001000L	/* Not used. */
#define PNG_CF_COPYSAFE  0x00000010L	/* Opaque data safe for copying. */

/*
 * Chunk types, not all of which have support implemented. Note that there are
 * others in the official extension set which we will never support (as they
 * are officially deprecated).
 */

#define CHUNK_IDAT	PNG_INT32('I','D','A','T')	/* Pixel data. */
#define CHUNK_IEND	PNG_INT32('I','E','N','D')	/* End of Image. */
#define CHUNK_IHDR	PNG_INT32('I','H','D','R')	/* Header. */
#define CHUNK_PLTE	PNG_INT32('P','L','T','E')	/* Palette. */

#define CHUNK_bKGD	PNG_INT32('b','K','G','D')	/* Background Color */
#define CHUNK_cHRM	PNG_INT32('c','H','R','M')	/* Chroma values. */
#define CHUNK_gAMA	PNG_INT32('g','A','M','A')	/* Gamma. */
#define CHUNK_hIST	PNG_INT32('h','I','S','T')	/* Histogram. */
#define CHUNK_iCCP	PNG_INT32('i','C','C','P')	/* Color profile. */
#define CHUNK_iTXt	PNG_INT32('i','T','X','t')	/* Internationalized
							 * text (comments,
							 * etc.) */
#define CHUNK_oFFs	PNG_INT32('o','F','F','s')	/* Image offset. */
#define CHUNK_pCAL	PNG_INT32('p','C','A','L')	/* Pixel calibration
							 * data. */
#define CHUNK_pHYs	PNG_INT32('p','H','Y','s')	/* Physical pixel
							 * dimensions. */
#define CHUNK_sBIT	PNG_INT32('s','B','I','T')	/* Significant bits */
#define CHUNK_sCAL	PNG_INT32('s','C','A','L')	/* Physical scale. */
#define CHUNK_sPLT	PNG_INT32('s','P','L','T')	/* Suggested
							 * palette. */
#define CHUNK_sRGB	PNG_INT32('s','R','G','B')	/* Standard RGB space
							 * declaration. */
#define CHUNK_tEXt	PNG_INT32('t','E','X','t')	/* Plain Latin-1
							 * text. */
#define CHUNK_tIME	PNG_INT32('t','I','M','E')	/* Time stamp. */
#define CHUNK_tRNS	PNG_INT32('t','R','N','S')	/* Transparency. */
#define CHUNK_zTXt	PNG_INT32('z','T','X','t')	/* Compressed Latin-1
							 * text. */

/*
 * Color flags.
 */

#define PNG_COLOR_INDEXED	1
#define PNG_COLOR_USED		2
#define PNG_COLOR_ALPHA		4

/*
 * Actual color types.
 */

#define PNG_COLOR_GRAY		0
#define PNG_COLOR_RGB		(PNG_COLOR_USED)
#define PNG_COLOR_PLTE		(PNG_COLOR_USED | PNG_COLOR_INDEXED)
#define PNG_COLOR_GRAYALPHA	(PNG_COLOR_GRAY | PNG_COLOR_ALPHA)
#define PNG_COLOR_RGBA		(PNG_COLOR_USED | PNG_COLOR_ALPHA)

/*
 * Compression Methods.
 */

#define PNG_COMPRESS_DEFLATE	0

/*
 * Filter Methods.
 */

#define PNG_FILTMETH_STANDARD	0

/*
 * Interlacing Methods.
 */

#define	PNG_INTERLACE_NONE	0
#define PNG_INTERLACE_ADAM7	1

/*
 * State information, used to store everything about the PNG image being
 * currently parsed or created.
 */

typedef struct {
    /*
     * PNG data source/destination channel/object/byte array.
     */

    Tcl_Channel channel;	/* Channel for from-file reads. */
    Tcl_Obj *objDataPtr;
    unsigned char *strDataBuf;	/* Raw source data for from-string reads. */
    int strDataLen;		/* Length of source data. */
    unsigned char *base64Data;	/* base64 encoded string data. */
    unsigned char base64Bits;	/* Remaining bits from last base64 read. */
    unsigned char base64State;	/* Current state of base64 decoder. */
    double alpha;		/* Alpha from -format option. */

    /*
     * Image header information.
     */

    unsigned char bitDepth;	/* Number of bits per pixel. */
    unsigned char colorType;	/* Grayscale, TrueColor, etc. */
    unsigned char compression;	/* Compression Mode (always zlib). */
    unsigned char filter;	/* Filter mode (0 - 3). */
    unsigned char interlace;	/* Type of interlacing (if any). */
    unsigned char numChannels;	/* Number of channels per pixel. */
    unsigned char bytesPerPixel;/* Bytes per pixel in scan line. */
    int bitScale;		/* Scale factor for RGB/Gray depths < 8. */
    int currentLine;		/* Current line being unfiltered. */
    unsigned char phase;	/* Interlacing phase (0..6). */
    Tk_PhotoImageBlock block;
    int blockLen;		/* Number of bytes in Tk image pixels. */

    /*
     * For containing data read from PLTE (palette) and tRNS (transparency)
     * chunks.
     */

    int paletteLen;		/* Number of PLTE entries (1..256). */
    int useTRNS;		/* Flag to indicate whether there was a
				 * palette given. */
    struct {
	unsigned char red;
	unsigned char green;
	unsigned char blue;
	unsigned char alpha;
    } palette[256];		/* Palette RGB/Transparency table. */
    unsigned char transVal[6];	/* Fully-transparent RGB/Gray Value. */

    /*
     * For compressing and decompressing IDAT chunks.
     */

    Tcl_ZlibStream stream;	/* Inflating or deflating stream; this one is
				 * not bound to a Tcl command. */
    Tcl_Obj *lastLineObj;	/* Last line of pixels, for unfiltering. */
    Tcl_Obj *thisLineObj;	/* Current line of pixels to process. */
    int lineSize;		/* Number of bytes in a PNG line. */
    int phaseSize;		/* Number of bytes/line in current phase. */
} PNGImage;

/*
 * Maximum size of various chunks.
 */

#define	PNG_PLTE_MAXSZ 768	/* 3 bytes/RGB entry, 256 entries max */
#define	PNG_TRNS_MAXSZ 256	/* 1-byte alpha, 256 entries max */

/*
 * Forward declarations of non-global functions defined in this file:
 */

static void		ApplyAlpha(PNGImage *pngPtr);
static int		CheckColor(Tcl_Interp *interp, PNGImage *pngPtr);
static inline int	CheckCRC(Tcl_Interp *interp, PNGImage *pngPtr,
			    unsigned long calculated);
static void		CleanupPNGImage(PNGImage *pngPtr);
static int		DecodeLine(Tcl_Interp *interp, PNGImage *pngPtr);
static int		DecodePNG(Tcl_Interp *interp, PNGImage *pngPtr,
			    Tcl_Obj *fmtObj, Tk_PhotoHandle imageHandle,
			    int destX, int destY);
static int		EncodePNG(Tcl_Interp *interp,
			    Tk_PhotoImageBlock *blockPtr, PNGImage *pngPtr);
static int		FileMatchPNG(Tcl_Channel chan, const char *fileName,
			    Tcl_Obj *fmtObj, int *widthPtr, int *heightPtr,
			    Tcl_Interp *interp);
static int		FileReadPNG(Tcl_Interp *interp, Tcl_Channel chan,
			    const char *fileName, Tcl_Obj *fmtObj,
			    Tk_PhotoHandle imageHandle, int destX, int destY,
			    int width, int height, int srcX, int srcY);
static int		FileWritePNG(Tcl_Interp *interp, const char *filename,
			    Tcl_Obj *fmtObj, Tk_PhotoImageBlock *blockPtr);
static int		InitPNGImage(Tcl_Interp *interp, PNGImage *pngPtr,
			    Tcl_Channel chan, Tcl_Obj *objPtr, int dir);
static inline unsigned char Paeth(int a, int b, int c);
static int		ParseFormat(Tcl_Interp *interp, Tcl_Obj *fmtObj,
			    PNGImage *pngPtr);
static int		ReadBase64(Tcl_Interp *interp, PNGImage *pngPtr,
			    unsigned char *destPtr, int destSz,
			    unsigned long *crcPtr);
static int		ReadByteArray(Tcl_Interp *interp, PNGImage *pngPtr,
			    unsigned char *destPtr, int destSz,
			    unsigned long *crcPtr);
static int		ReadData(Tcl_Interp *interp, PNGImage *pngPtr,
			    unsigned char *destPtr, int destSz,
			    unsigned long *crcPtr);
static int		ReadChunkHeader(Tcl_Interp *interp, PNGImage *pngPtr,
			    int *sizePtr, unsigned long *typePtr,
			    unsigned long *crcPtr);
static int		ReadIDAT(Tcl_Interp *interp, PNGImage *pngPtr,
			    int chunkSz, unsigned long crc);
static int		ReadIHDR(Tcl_Interp *interp, PNGImage *pngPtr);
static inline int	ReadInt32(Tcl_Interp *interp, PNGImage *pngPtr,
			    unsigned long *resultPtr, unsigned long *crcPtr);
static int		ReadPLTE(Tcl_Interp *interp, PNGImage *pngPtr,
			    int chunkSz, unsigned long crc);
static int		ReadTRNS(Tcl_Interp *interp, PNGImage *pngPtr,
			    int chunkSz, unsigned long crc);
static int		SkipChunk(Tcl_Interp *interp, PNGImage *pngPtr,
			    int chunkSz, unsigned long crc);
static int		StringMatchPNG(Tcl_Obj *dataObj, Tcl_Obj *fmtObj,
			    int *widthPtr, int *heightPtr,
			    Tcl_Interp *interp);
static int		StringReadPNG(Tcl_Interp *interp, Tcl_Obj *dataObj,
			    Tcl_Obj *fmtObj, Tk_PhotoHandle imageHandle,
			    int destX, int destY, int width, int height,
			    int srcX, int srcY);
static int		StringWritePNG(Tcl_Interp *interp, Tcl_Obj *fmtObj,
			    Tk_PhotoImageBlock *blockPtr);
static int		UnfilterLine(Tcl_Interp *interp, PNGImage *pngPtr);
static inline int	WriteByte(Tcl_Interp *interp, PNGImage *pngPtr,
			    unsigned char c, unsigned long *crcPtr);
static inline int	WriteChunk(Tcl_Interp *interp, PNGImage *pngPtr,
			    unsigned long chunkType,
			    const unsigned char *dataPtr, int dataSize);
static int		WriteData(Tcl_Interp *interp, PNGImage *pngPtr,
			    const unsigned char *srcPtr, int srcSz,
			    unsigned long *crcPtr);
static int		WriteExtraChunks(Tcl_Interp *interp,
			    PNGImage *pngPtr);
static int		WriteIHDR(Tcl_Interp *interp, PNGImage *pngPtr,
			    Tk_PhotoImageBlock *blockPtr);
static int		WriteIDAT(Tcl_Interp *interp, PNGImage *pngPtr,
			    Tk_PhotoImageBlock *blockPtr);
static inline int	WriteInt32(Tcl_Interp *interp, PNGImage *pngPtr,
			    unsigned long l, unsigned long *crcPtr);

/*
 * The format record for the PNG file format:
 */

Tk_PhotoImageFormat tkImgFmtPNG = {
    "png",			/* name */
    FileMatchPNG,		/* fileMatchProc */
    StringMatchPNG,		/* stringMatchProc */
    FileReadPNG,		/* fileReadProc */
    StringReadPNG,		/* stringReadProc */
    FileWritePNG,		/* fileWriteProc */
    StringWritePNG,		/* stringWriteProc */
    NULL
};

/*
 *----------------------------------------------------------------------
 *
 * InitPNGImage --
 *
 *	This function is invoked by each of the Tk image handler procs
 *	(MatchStringProc, etc.) to initialize state information used during
 *	the course of encoding or decoding a PNG image.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if initialization failed.
 *
 * Side effects:
 *	The reference count of the -data Tcl_Obj*, if any, is incremented.
 *
 *----------------------------------------------------------------------
 */

static int
InitPNGImage(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    Tcl_Channel chan,
    Tcl_Obj *objPtr,
    int dir)
{
    memset(pngPtr, 0, sizeof(PNGImage));

    pngPtr->channel = chan;
    pngPtr->alpha = 1.0;

    /*
     * If decoding from a -data string object, increment its reference count
     * for the duration of the decode and get its length and byte array for
     * reading with ReadData().
     */

    if (objPtr) {
	Tcl_IncrRefCount(objPtr);
	pngPtr->objDataPtr = objPtr;
	pngPtr->strDataBuf =
		Tcl_GetByteArrayFromObj(objPtr, &pngPtr->strDataLen);
    }

    /*
     * Initialize the palette transparency table to fully opaque.
     */

    memset(pngPtr->palette, 255, sizeof(pngPtr->palette));

    /*
     * Initialize Zlib inflate/deflate stream.
     */

    if (Tcl_ZlibStreamInit(NULL, dir, TCL_ZLIB_FORMAT_ZLIB,
	    TCL_ZLIB_COMPRESS_DEFAULT, NULL, &pngPtr->stream) != TCL_OK) {
	Tcl_SetResult(interp, "zlib initialization failed", TCL_STATIC);
	if (objPtr) {
	    Tcl_DecrRefCount(objPtr);
	}
	return TCL_ERROR;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * CleanupPNGImage --
 *
 *	This function is invoked by each of the Tk image handler procs
 *	(MatchStringProc, etc.) prior to returning to Tcl in order to clean up
 *	any allocated memory and call other cleanup handlers such as zlib's
 *	inflateEnd/deflateEnd.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The reference count of the -data Tcl_Obj*, if any, is decremented.
 *	Buffers are freed, streams are closed. The PNGImage should not be used
 *	for any purpose without being reinitialized post-cleanup.
 *
 *----------------------------------------------------------------------
 */

static void
CleanupPNGImage(
    PNGImage *pngPtr)
{
    /*
     * Don't need the object containing the -data value anymore.
     */

    if (pngPtr->objDataPtr) {
	Tcl_DecrRefCount(pngPtr->objDataPtr);
    }

    /*
     * Discard pixel buffer.
     */

    if (pngPtr->stream) {
	Tcl_ZlibStreamClose(pngPtr->stream);
    }

    if (pngPtr->block.pixelPtr) {
	ckfree(pngPtr->block.pixelPtr);
    }
    if (pngPtr->thisLineObj) {
	Tcl_DecrRefCount(pngPtr->thisLineObj);
    }
    if (pngPtr->lastLineObj) {
	Tcl_DecrRefCount(pngPtr->lastLineObj);
    }

    memset(pngPtr, 0, sizeof(PNGImage));
}

/*
 *----------------------------------------------------------------------
 *
 * ReadBase64 --
 *
 *	This function is invoked to read the specified number of bytes from
 *	base-64 encoded image data.
 *
 *	Note: It would be better if the Tk_PhotoImage stuff handled this by
 *	creating a channel from the -data value, which would take care of
 *	base64 decoding and made the data readable as if it were coming from a
 *	file.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error occurs.
 *
 * Side effects:
 *	The file position will change. The running CRC is updated if a pointer
 *	to it is provided.
 *
 *----------------------------------------------------------------------
 */

static int
ReadBase64(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    unsigned char *destPtr,
    int destSz,
    unsigned long *crcPtr)
{
    static const unsigned char from64[] = {
	0x82, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x80, 0x80,
	0x83, 0x80, 0x80, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x80,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x3e,
	0x83, 0x83, 0x83, 0x3f, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a,
	0x3b, 0x3c, 0x3d, 0x83, 0x83, 0x83, 0x81, 0x83, 0x83, 0x83, 0x00,
	0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b,
	0x0c, 0x0d, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
	0x17, 0x18, 0x19, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x1a, 0x1b,
	0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26,
	0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31,
	0x32, 0x33, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83, 0x83,
	0x83, 0x83
    };

    /*
     * Definitions for the base-64 decoder.
     */

#define PNG64_SPECIAL	0x80	/* Flag bit */
#define PNG64_SPACE	0x80	/* Whitespace */
#define PNG64_PAD	0x81	/* Padding */
#define PNG64_DONE	0x82	/* End of data */
#define PNG64_BAD	0x83	/* Ooooh, naughty! */

    while (destSz && pngPtr->strDataLen) {
	unsigned char c = 0;
	unsigned char c64 = from64[*pngPtr->strDataBuf++];

	pngPtr->strDataLen--;

	if (PNG64_SPACE == c64) {
	    continue;
	}

	if (c64 & PNG64_SPECIAL) {
	    c = (unsigned char) pngPtr->base64Bits;
	} else {
	    switch (pngPtr->base64State++) {
	    case 0:
		pngPtr->base64Bits = c64 << 2;
		continue;
	    case 1:
		c = (unsigned char) (pngPtr->base64Bits | (c64 >> 4));
		pngPtr->base64Bits = (c64 & 0xF) << 4;
		break;
	    case 2:
		c = (unsigned char) (pngPtr->base64Bits | (c64 >> 2));
		pngPtr->base64Bits = (c64 & 0x3) << 6;
		break;
	    case 3:
		c = (unsigned char) (pngPtr->base64Bits | c64);
		pngPtr->base64State = 0;
		pngPtr->base64Bits = 0;
		break;
	    }
	}

	if (crcPtr) {
	    *crcPtr = Tcl_ZlibCRC32(*crcPtr, &c, 1);
	}

	if (destPtr) {
	    *destPtr++ = c;
	}

	destSz--;

	if (c64 & PNG64_SPECIAL) {
	    break;
	}
    }

    if (destSz) {
	Tcl_SetResult(interp, "Unexpected end of image data", TCL_STATIC);
	return TCL_ERROR;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ReadByteArray --
 *
 *	This function is invoked to read the specified number of bytes from a
 *	non-base64-encoded byte array provided via the -data option.
 *
 *	Note: It would be better if the Tk_PhotoImage stuff handled this by
 *	creating a channel from the -data value and made the data readable as
 *	if it were coming from a file.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error occurs.
 *
 * Side effects:
 *	The file position will change. The running CRC is updated if a pointer
 *	to it is provided.
 *
 *----------------------------------------------------------------------
 */

static int
ReadByteArray(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    unsigned char *destPtr,
    int destSz,
    unsigned long *crcPtr)
{
    /*
     * Check to make sure the number of requested bytes are available.
     */

    if (pngPtr->strDataLen < destSz) {
	Tcl_SetResult(interp, "Unexpected end of image data", TCL_STATIC);
	return TCL_ERROR;
    }

    while (destSz) {
	int blockSz = PNG_MIN(destSz, PNG_BLOCK_SZ);

	memcpy(destPtr, pngPtr->strDataBuf, blockSz);

	pngPtr->strDataBuf += blockSz;
	pngPtr->strDataLen -= blockSz;

	if (crcPtr) {
	    *crcPtr = Tcl_ZlibCRC32(*crcPtr, destPtr, blockSz);
	}

	destPtr += blockSz;
	destSz -= blockSz;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ReadData --
 *
 *	This function is invoked to read the specified number of bytes from
 *	the image file or data. It is a wrapper around the choice of byte
 *	array Tcl_Obj or Tcl_Channel which depends on whether the image data
 *	is coming from a file or -data.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error occurs.
 *
 * Side effects:
 *	The file position will change. The running CRC is updated if a pointer
 *	to it is provided.
 *
 *----------------------------------------------------------------------
 */

static int
ReadData(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    unsigned char *destPtr,
    int destSz,
    unsigned long *crcPtr)
{
    if (pngPtr->base64Data) {
	return ReadBase64(interp, pngPtr, destPtr, destSz, crcPtr);
    } else if (pngPtr->strDataBuf) {
	return ReadByteArray(interp, pngPtr, destPtr, destSz, crcPtr);
    }

    while (destSz) {
	int blockSz = PNG_MIN(destSz, PNG_BLOCK_SZ);

	blockSz = Tcl_Read(pngPtr->channel, (char *)destPtr, blockSz);

	/*
	 * Check for read failure.
	 */

	if (blockSz < 0) {
	    /* TODO: failure info... */
	    Tcl_SetResult(interp, "Channel read failed", TCL_STATIC);
	    return TCL_ERROR;
	}

	/*
	 * Update CRC, pointer, and remaining count if anything was read.
	 */

	if (blockSz) {
	    if (crcPtr) {
		*crcPtr = Tcl_ZlibCRC32(*crcPtr, destPtr, blockSz);
	    }

	    destPtr += blockSz;
	    destSz -= blockSz;
	}

	/*
	 * Check for EOF before all desired data was read.
	 */

	if (destSz && Tcl_Eof(pngPtr->channel)) {
	    Tcl_SetResult(interp, "Unexpected end of file ", TCL_STATIC);
	    return TCL_ERROR;
	}
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ReadInt32 --
 *
 *	This function is invoked to read a 32-bit integer in network byte
 *	order from the image data and return the value in host byte order.
 *	This is used, for example, to read the 32-bit CRC value for a chunk
 *	stored in the image file for comparison with the calculated CRC value.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error occurs.
 *
 * Side effects:
 *	The file position will change. The running CRC is updated if a pointer
 *	to it is provided.
 *
 *----------------------------------------------------------------------
 */

static inline int
ReadInt32(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    unsigned long *resultPtr,
    unsigned long *crcPtr)
{
    unsigned char p[4];

    if (ReadData(interp, pngPtr, p, 4, crcPtr) == TCL_ERROR) {
	return TCL_ERROR;
    }

    *resultPtr = PNG_INT32(p[0], p[1], p[2], p[3]);

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * CheckCRC --
 *
 *	This function is reads the final 4-byte integer CRC from a chunk and
 *	compares it to the running CRC calculated over the chunk type and data
 *	fields.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error or CRC mismatch occurs.
 *
 * Side effects:
 *	The file position will change.
 *
 *----------------------------------------------------------------------
 */

static inline int
CheckCRC(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    unsigned long calculated)
{
    unsigned long chunked;

    /*
     * Read the CRC field at the end of the chunk.
     */

    if (ReadInt32(interp, pngPtr, &chunked, NULL) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Compare the read CRC to what we calculate to make sure they match.
     */

    if (calculated != chunked) {
	Tcl_SetResult(interp, "CRC check failed", TCL_STATIC);
	return TCL_ERROR;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * SkipChunk --
 *
 *	This function is used to skip a PNG chunk that is not used by this
 *	implementation. Given the input stream has had the chunk length and
 *	chunk type fields already read, this function will read the number of
 *	bytes indicated by the chunk length, plus four for the CRC, and will
 *	verify that CRC is correct for the skipped data.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error or CRC mismatch occurs.
 *
 * Side effects:
 *	The file position will change.
 *
 *----------------------------------------------------------------------
 */

static int
SkipChunk(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    int chunkSz,
    unsigned long crc)
{
    unsigned char buffer[PNG_BLOCK_SZ];

    /*
     * Skip data in blocks until none is left. Read up to PNG_BLOCK_SZ bytes
     * at a time, rather than trusting the claimed chunk size, which may not
     * be trustworthy.
     */

    while (chunkSz) {
	int blockSz = PNG_MIN(chunkSz, PNG_BLOCK_SZ);

	if (ReadData(interp, pngPtr, buffer, blockSz, &crc) == TCL_ERROR) {
	    return TCL_ERROR;
	}

	chunkSz -= blockSz;
    }

    if (CheckCRC(interp, pngPtr, crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    return TCL_OK;
}

/*
 * 4.3. Summary of standard chunks
 *
 * This table summarizes some properties of the standard chunk types. 
 *
 *	Critical chunks (must appear in this order, except PLTE is optional):
 *
 *		Name   Multiple	 Ordering constraints OK?
 *
 *		IHDR	No	 Must be first
 *		PLTE	No	 Before IDAT
 *		IDAT	Yes	 Multiple IDATs must be consecutive
 *		IEND	No	 Must be last
 *
 *	Ancillary chunks (need not appear in this order):
 *
 *		Name   Multiple	 Ordering constraints OK?
 *
 *		cHRM	No	 Before PLTE and IDAT
 *		gAMA	No	 Before PLTE and IDAT
 *		iCCP	No	 Before PLTE and IDAT
 *		sBIT	No	 Before PLTE and IDAT
 *		sRGB	No	 Before PLTE and IDAT
 *		bKGD	No	 After PLTE; before IDAT
 *		hIST	No	 After PLTE; before IDAT
 *		tRNS	No	 After PLTE; before IDAT
 *		pHYs	No	 Before IDAT
 *		sPLT	Yes	 Before IDAT
 *		tIME	No	 None
 *		iTXt	Yes	 None
 *		tEXt	Yes	 None
 *		zTXt	Yes	 None
 *
 *	[From the PNG specification.]
 */

/*
 *----------------------------------------------------------------------
 *
 * ReadChunkHeader --
 *
 *	This function is used at the start of each chunk to extract the
 *	four-byte chunk length and four-byte chunk type fields. It will
 *	continue reading until it finds a chunk type that is handled by this
 *	implementation, checking the CRC of any chunks it skips.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error occurs or an unknown critical
 *	chunk type is encountered.
 *
 * Side effects:
 *	The file position will change. The running CRC is updated.
 *
 *----------------------------------------------------------------------
 */

static int
ReadChunkHeader(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    int *sizePtr,
    unsigned long *typePtr,
    unsigned long *crcPtr)
{
    unsigned long chunkType = 0;
    int chunkSz = 0;
    unsigned long crc = 0;

    /*
     * Continue until finding a chunk type that is handled.
     */

    while (!chunkType) {
	unsigned long temp;
	unsigned char pc[4];
	int i;

	/*
	 * Read the 4-byte length field for the chunk. The length field is not
	 * included in the CRC calculation, so the running CRC must be reset
	 * afterward. Limit chunk lengths to INT_MAX, to align with the
	 * maximum size for Tcl_Read, Tcl_GetByteArrayFromObj, etc.
	 */

	if (ReadData(interp, pngPtr, pc, 4, NULL) == TCL_ERROR) {
	    return TCL_ERROR;
	}

	temp = PNG_INT32(pc[0], pc[1], pc[2], pc[3]);

	if (temp > INT_MAX) {
	    Tcl_SetResult(interp, "Chunk size is out of supported range "
		    "on this architecture", TCL_STATIC);
	    return TCL_ERROR;
	}

	chunkSz = (int) temp;
	crc = Tcl_ZlibCRC32(0, NULL, 0);

	/*
	 * Read the 4-byte chunk type.
	 */

	if (ReadData(interp, pngPtr, pc, 4, &crc) == TCL_ERROR) {
	    return TCL_ERROR;
	}

	/*
	 * Convert it to a host-order integer for simple comparison.
	 */

	chunkType = PNG_INT32(pc[0], pc[1], pc[2], pc[3]);

	/*
	 * Check to see if this is a known/supported chunk type. Note that the
	 * PNG specs require non-critical (i.e., ancillary) chunk types that
	 * are not recognized to be ignored, rather than be treated as an
	 * error. It does, however, recommend that an unknown critical chunk
	 * type be treated as a failure.
	 *
	 * This switch/loop acts as a filter of sorts for undesired chunk
	 * types. The chunk type should still be checked elsewhere for
	 * determining it is in the correct order.
	 */

	switch (chunkType) {
	    /*
	     * These chunk types are required and/or supported.
	     */

	case CHUNK_IDAT:
	case CHUNK_IEND:
	case CHUNK_IHDR:
	case CHUNK_PLTE:
	case CHUNK_tRNS:
	    break;

	    /*
	     * These chunk types are part of the standard, but are not used by
	     * this implementation (at least not yet). Note that these are all
	     * ancillary chunks (lowercase first letter).
	     */

	case CHUNK_bKGD:
	case CHUNK_cHRM:
	case CHUNK_gAMA:
	case CHUNK_hIST:
	case CHUNK_iCCP:
	case CHUNK_iTXt:
	case CHUNK_oFFs:
	case CHUNK_pCAL:
	case CHUNK_pHYs:
	case CHUNK_sBIT:
	case CHUNK_sCAL:
	case CHUNK_sPLT:
	case CHUNK_sRGB:
	case CHUNK_tEXt:
	case CHUNK_tIME:
	case CHUNK_zTXt:
	    /*
	     * TODO: might want to check order here.
	     */

	    if (SkipChunk(interp, pngPtr, chunkSz, crc) == TCL_ERROR) {
		return TCL_ERROR;
	    }

	    chunkType = 0;
	    break;

	default:
	    /*
	     * Unknown chunk type. If it's critical, we can't continue.
	     */

	    if (!(chunkType & PNG_CF_ANCILLARY)) {
		Tcl_SetResult(interp,
			"Encountered an unsupported criticial chunk type",
			TCL_STATIC);
		return TCL_ERROR;
	    }

	    /*
	     * Check to see if the chunk type has legal bytes.
	     */

	    for (i=0 ; i<4 ; i++) {
		if ((pc[i] < 65) || (pc[i] > 122) ||
			((pc[i] > 90) && (pc[i] < 97))) {
		    Tcl_SetResult(interp, "Invalid chunk type", TCL_STATIC);
		    return TCL_ERROR;
		}
	    }

	    /*
	     * It seems to be an otherwise legally labelled ancillary chunk
	     * that we don't want, so skip it after at least checking its CRC.
	     */

	    if (SkipChunk(interp, pngPtr, chunkSz, crc) == TCL_ERROR) {
		return TCL_ERROR;
	    }

	    chunkType = 0;
	}
    }

    /*
     * Found a known chunk type that's handled, albiet possibly not in the
     * right order. Send back the chunk type (for further checking or
     * handling), the chunk size and the current CRC for the rest of the
     * calculation.
     */

    *typePtr = chunkType;
    *sizePtr = chunkSz;
    *crcPtr = crc;

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * CheckColor --
 *
 *	Do validation on color type, depth, and related information, and
 *	calculates storage requirements and offsets based on image dimensions
 *	and color.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if color information is invalid or some other
 *	failure occurs.
 *
 * Side effects:
 *	None
 *
 *----------------------------------------------------------------------
 */

static int
CheckColor(
    Tcl_Interp *interp,
    PNGImage *pngPtr)
{
    int result = TCL_OK;
    int offset;

    /*
     * Verify the color type is valid and the bit depth is allowed.
     */

    switch (pngPtr->colorType) {
    case PNG_COLOR_GRAY:
	pngPtr->numChannels = 1;
	if ((1 != pngPtr->bitDepth) && (2 != pngPtr->bitDepth) &&
		(4 != pngPtr->bitDepth) && (8 != pngPtr->bitDepth) &&
		(16 != pngPtr->bitDepth)) {
	    result = TCL_ERROR;
	}
	break;

    case PNG_COLOR_RGB:
	pngPtr->numChannels = 3;
	if ((8 != pngPtr->bitDepth) && (16 != pngPtr->bitDepth)) {
	    result = TCL_ERROR;
	}
	break;

    case PNG_COLOR_PLTE:
	pngPtr->numChannels = 1;
	if ((1 != pngPtr->bitDepth) && (2 != pngPtr->bitDepth) &&
		(4 != pngPtr->bitDepth) && (8 != pngPtr->bitDepth)) {
	    result = TCL_ERROR;
	}
	break;

    case PNG_COLOR_GRAYALPHA:
	pngPtr->numChannels = 2;
	if ((8 != pngPtr->bitDepth) && (16 != pngPtr->bitDepth)) {
	    result = TCL_ERROR;
	}
	break;

    case PNG_COLOR_RGBA:
	pngPtr->numChannels = 4;
	if ((8 != pngPtr->bitDepth) && (16 != pngPtr->bitDepth)) {
	    result = TCL_ERROR;
	}
	break;

    default:
	Tcl_SetResult(interp, "Unknown Color Type field", TCL_STATIC);
	return TCL_ERROR;
    }

    if (TCL_ERROR == result) {
	Tcl_SetResult(interp, "Bit depth is not allowed for given color type",
		TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * Set up the Tk photo block's pixel size and channel offsets. offset
     * array elements should already be 0 from the memset during InitPNGImage.
     */

    offset = (pngPtr->bitDepth > 8) ? 2 : 1;

    if (pngPtr->colorType & PNG_COLOR_USED) {
	pngPtr->block.pixelSize = offset * 4;
	pngPtr->block.offset[1] = offset;
	pngPtr->block.offset[2] = offset * 2;
	pngPtr->block.offset[3] = offset * 3;
    } else {
	pngPtr->block.pixelSize = offset * 2;
	pngPtr->block.offset[3] = offset;
    }

    /*
     * Calculate the block pitch, which is the number of bytes per line in the
     * image, given image width and depth of color. Make sure that it it isn't
     * larger than Tk can handle.
     */

    if (pngPtr->block.width > INT_MAX / pngPtr->block.pixelSize) {
	Tcl_SetResult(interp,
		"Image pitch is out of supported range on this architecture",
		TCL_STATIC);
	return TCL_ERROR;
    }

    pngPtr->block.pitch = pngPtr->block.pixelSize * pngPtr->block.width;

    /*
     * Calculate the total size of the image as represented to Tk given pitch
     * and image height. Make sure that it isn't larger than Tk can handle.
     */

    if (pngPtr->block.height > INT_MAX / pngPtr->block.pitch) {
	Tcl_SetResult(interp, "Image total size is out of supported range "
		"on this architecture", TCL_STATIC);
	return TCL_ERROR;
    }

    pngPtr->blockLen = pngPtr->block.height * pngPtr->block.pitch;

    /*
     * Determine number of bytes per pixel in the source for later use.
     */

    switch (pngPtr->colorType) {
    case PNG_COLOR_GRAY:
	pngPtr->bytesPerPixel = (pngPtr->bitDepth > 8) ? 2 : 1;
	break;
    case PNG_COLOR_RGB:
	pngPtr->bytesPerPixel = (pngPtr->bitDepth > 8) ? 6 : 3;
	break;
    case PNG_COLOR_PLTE:
	pngPtr->bytesPerPixel = 1;
	break;
    case PNG_COLOR_GRAYALPHA:
	pngPtr->bytesPerPixel = (pngPtr->bitDepth > 8) ? 4 : 2;
	break;
    case PNG_COLOR_RGBA:
	pngPtr->bytesPerPixel = (pngPtr->bitDepth > 8) ? 8 : 4;
	break;
    default:
	Tcl_SetResult(interp, "internal error - unknown color type",
		TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * Calculate scale factor for bit depths less than 8, in order to adjust
     * them to a minimum of 8 bits per pixel in the Tk image.
     */

    if (pngPtr->bitDepth < 8) {
	pngPtr->bitScale = 255 / (int)(pow(2, pngPtr->bitDepth) - 1);
    } else {
	pngPtr->bitScale = 1;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ReadIHDR --
 *
 *	This function reads the PNG header from the beginning of a PNG file
 *	and returns the dimensions of the image.
 *
 * Results:
 *	The return value is 1 if file "f" appears to start with a valid PNG
 *	header, 0 otherwise. If the header is valid, then *widthPtr and
 *	*heightPtr are modified to hold the dimensions of the image.
 *
 * Side effects:
 *	The access position in f advances.
 *
 *----------------------------------------------------------------------
 */

static int
ReadIHDR(
    Tcl_Interp *interp,
    PNGImage *pngPtr)
{
    unsigned char sigBuf[PNG_SIG_SZ];
    unsigned long chunkType;
    int chunkSz;
    unsigned long crc;
    unsigned long width, height;
    int mismatch;

    /*
     * Read the appropriate number of bytes for the PNG signature.
     */

    if (ReadData(interp, pngPtr, sigBuf, PNG_SIG_SZ, NULL) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Compare the read bytes to the expected signature.
     */

    mismatch = memcmp(sigBuf, pngSignature, PNG_SIG_SZ);

    /*
     * If reading from string, reset position and try base64 decode.
     */

    if (mismatch && pngPtr->strDataBuf) {
	pngPtr->strDataBuf = Tcl_GetByteArrayFromObj(pngPtr->objDataPtr,
		&pngPtr->strDataLen);
	pngPtr->base64Data = pngPtr->strDataBuf;

	if (ReadData(interp, pngPtr, sigBuf, PNG_SIG_SZ, NULL) == TCL_ERROR) {
	    return TCL_ERROR;
	}

	mismatch = memcmp(sigBuf, pngSignature, PNG_SIG_SZ);
    }

    if (mismatch) {
	Tcl_SetResult(interp, "Data stream does not have a PNG signature",
		TCL_STATIC);
	return TCL_ERROR;
    }

    if (ReadChunkHeader(interp, pngPtr, &chunkSz, &chunkType,
	    &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Read in the IHDR (header) chunk for width, height, etc.
     *
     * The first chunk in the file must be the IHDR (headr) chunk.
     */

    if (chunkType != CHUNK_IHDR) {
	Tcl_SetResult(interp, "Expected IHDR chunk type", TCL_STATIC);
	return TCL_ERROR;
    }

    if (chunkSz != 13) {
	Tcl_SetResult(interp, "Invalid IHDR chunk size", TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * Read and verify the image width and height to be sure Tk can handle its
     * dimensions. The PNG specification does not permit zero-width or
     * zero-height images.
     */

    if (ReadInt32(interp, pngPtr, &width, &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    if (ReadInt32(interp, pngPtr, &height, &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    if (!width || !height || (width > INT_MAX) || (height > INT_MAX)) {
	Tcl_SetResult(interp,
		"Image dimensions are invalid or beyond architecture limits",
		TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * Set height and width for the Tk photo block.
     */

    pngPtr->block.width = (int) width;
    pngPtr->block.height = (int) height;

    /*
     * Read and the Bit Depth and Color Type.
     */

    if (ReadData(interp, pngPtr, &pngPtr->bitDepth, 1, &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    if (ReadData(interp, pngPtr, &pngPtr->colorType, 1, &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Verify that the color type is valid, the bit depth is allowed for the
     * color type, and calculate the number of channels and pixel depth (bits
     * per pixel * channels). Also set up offsets and sizes in the Tk photo
     * block for the pixel data.
     */

    if (CheckColor(interp, pngPtr) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Only one compression method is currently defined by the standard.
     */

    if (ReadData(interp, pngPtr, &pngPtr->compression, 1, &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    if (PNG_COMPRESS_DEFLATE != pngPtr->compression) {
	Tcl_SetResult(interp, "Unknown compression method", TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * Only one filter method is currently defined by the standard; the method
     * has five actual filter types associated with it.
     */

    if (ReadData(interp, pngPtr, &pngPtr->filter, 1, &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    if (PNG_FILTMETH_STANDARD != pngPtr->filter) {
	Tcl_SetResult(interp, "Unknown filter method", TCL_STATIC);
	return TCL_ERROR;
    }

    if (ReadData(interp, pngPtr, &pngPtr->interlace, 1, &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    switch (pngPtr->interlace) {
    case PNG_INTERLACE_NONE:
    case PNG_INTERLACE_ADAM7:
	break;

    default:
	Tcl_SetResult(interp, "Unknown interlace method", TCL_STATIC);
	return TCL_ERROR;
    }

    return CheckCRC(interp, pngPtr, crc);
}

/*
 *----------------------------------------------------------------------
 *
 * ReadPLTE --
 *
 *	This function reads the PLTE (indexed color palette) chunk data from
 *	the PNG file and populates the palette table in the PNGImage
 *	structure.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error occurs or the PLTE chunk is
 *	invalid.
 *
 * Side effects:
 *	The access position in f advances.
 *
 *----------------------------------------------------------------------
 */

static int
ReadPLTE(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    int chunkSz,
    unsigned long crc)
{
    unsigned char buffer[PNG_PLTE_MAXSZ];
    int i, c;

    /*
     * This chunk is mandatory for color type 3 and forbidden for 2 and 6.
     */

    switch (pngPtr->colorType) {
    case PNG_COLOR_GRAY:
    case PNG_COLOR_GRAYALPHA:
	Tcl_SetResult(interp, "PLTE chunk type forbidden for grayscale",
		TCL_STATIC);
	return TCL_ERROR;

    default:
	break;
    }

    /*
     * The palette chunk contains from 1 to 256 palette entries. Each entry
     * consists of a 3-byte RGB value. It must therefore contain a non-zero
     * multiple of 3 bytes, up to 768.
     */

    if (!chunkSz || (chunkSz > PNG_PLTE_MAXSZ) || (chunkSz % 3)) {
	Tcl_SetResult(interp, "Invalid palette chunk size", TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * Read the palette contents and stash them for later, possibly.
     */

    if (ReadData(interp, pngPtr, buffer, chunkSz, &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    if (CheckCRC(interp, pngPtr, crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Stash away the palette entries and entry count for later mapping each
     * pixel's palette index to its color.
     */

    for (i=0, c=0 ; c<chunkSz ; i++) {
	pngPtr->palette[i].red = buffer[c++];
	pngPtr->palette[i].green = buffer[c++];
	pngPtr->palette[i].blue = buffer[c++];
    }

    pngPtr->paletteLen = i;
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ReadTRNS --
 *
 *	This function reads the tRNS (transparency) chunk data from the PNG
 *	file and populates the alpha field of the palette table in the
 *	PNGImage structure or the single color transparency, as appropriate
 *	for the color type.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error occurs or the tRNS chunk is
 *	invalid.
 *
 * Side effects:
 *	The access position in f advances.
 *
 *----------------------------------------------------------------------
 */

static int
ReadTRNS(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    int chunkSz,
    unsigned long crc)
{
    unsigned char buffer[PNG_TRNS_MAXSZ];
    int i;

    if (pngPtr->colorType & PNG_COLOR_ALPHA) {
	Tcl_SetResult(interp,
		"tRNS chunk not allowed color types with a full alpha channel",
		TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * For indexed color, there is up to one single-byte transparency value
     * per palette entry (thus a max of 256).
     */

    if (chunkSz > PNG_TRNS_MAXSZ) {
	Tcl_SetResult(interp, "Invalid tRNS chunk size", TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * Read in the raw transparency information.
     */

    if (ReadData(interp, pngPtr, buffer, chunkSz, &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    if (CheckCRC(interp, pngPtr, crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    switch (pngPtr->colorType) {
    case PNG_COLOR_GRAYALPHA:
    case PNG_COLOR_RGBA:
	break;

    case PNG_COLOR_PLTE:
	/*
	 * The number of tRNS entries must be less than or equal to the number
	 * of PLTE entries, and consists of a single-byte alpha level for the
	 * corresponding PLTE entry.
	 */

	if (chunkSz > pngPtr->paletteLen) {
	    Tcl_SetResult(interp,
		    "Size of tRNS chunk is too large for the palette",
		    TCL_STATIC);
	    return TCL_ERROR;
	}

	for (i=0 ; i<chunkSz ; i++) {
	    pngPtr->palette[i].alpha = buffer[i];
	}
	break;

    case PNG_COLOR_GRAY:
	/*
	 * Grayscale uses a single 2-byte gray level, which we'll store in
	 * palette index 0, since we're not using the palette.
	 */

	if (chunkSz != 2) {
	    Tcl_SetResult(interp,
		    "Invalid tRNS chunk size - must 2 bytes for grayscale",
		    TCL_STATIC);
	    return TCL_ERROR;
	}

	/*
	 * According to the PNG specs, if the bit depth is less than 16, then
	 * only the lower byte is used.
	 */

	if (16 == pngPtr->bitDepth) {
	    pngPtr->transVal[0] = buffer[0];
	    pngPtr->transVal[1] = buffer[1];
	} else {
	    pngPtr->transVal[0] = buffer[1];
	}
	pngPtr->useTRNS = 1;
	break;

    case PNG_COLOR_RGB:
	/*
	 * TrueColor uses a single RRGGBB triplet.
	 */

	if (chunkSz != 6) {
	    Tcl_SetResult(interp,
		    "Invalid tRNS chunk size - must 6 bytes for RGB",
		    TCL_STATIC);
	    return TCL_ERROR;
	}

	/*
	 * According to the PNG specs, if the bit depth is less than 16, then
	 * only the lower byte is used. But the tRNS chunk still contains two
	 * bytes per channel.
	 */

	if (16 == pngPtr->bitDepth) {
	    memcpy(pngPtr->transVal, buffer, 6);
	} else {
	    pngPtr->transVal[0] = buffer[1];
	    pngPtr->transVal[1] = buffer[3];
	    pngPtr->transVal[2] = buffer[5];
	}
	pngPtr->useTRNS = 1;
	break;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Paeth --
 *
 *	Utility function for applying the Paeth filter to a pixel. The Paeth
 *	filter is a linear function of the pixel to be filtered and the pixels
 *	to the left, above, and above-left of the pixel to be unfiltered.
 *
 * Results:
 *	Result of the Paeth function for the left, above, and above-left
 *	pixels.
 *
 * Side effects:
 *	None
 *
 *----------------------------------------------------------------------
 */

static inline unsigned char
Paeth(
    int a,
    int b,
    int c)
{
    int pa = abs(b - c);
    int pb = abs(a - c);
    int pc = abs(a + b - c - c);

    if ((pa <= pb) && (pa <= pc)) {
	return (unsigned char) a;
    }

    if (pb <= pc) {
	return (unsigned char) b;
    }

    return (unsigned char) c;
}

/*
 *----------------------------------------------------------------------
 *
 * UnfilterLine --
 *
 *	Applies the filter algorithm specified in first byte of a line to the
 *	line of pixels being read from a PNG image.
 *
 *	PNG specifies four filter algorithms (Sub, Up, Average, and Paeth)
 *	that combine a pixel's value with those of other pixels in the same
 *	and/or previous lines. Filtering is intended to make an image more
 *	compressible.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if the filter type is not recognized.
 *
 * Side effects:
 *	Pixel data in thisLineObj are modified.
 *
 *----------------------------------------------------------------------
 */

static int
UnfilterLine(
    Tcl_Interp *interp,
    PNGImage *pngPtr)
{
    unsigned char *thisLine =
	    Tcl_GetByteArrayFromObj(pngPtr->thisLineObj, NULL);
    unsigned char *lastLine =
	    Tcl_GetByteArrayFromObj(pngPtr->lastLineObj, NULL);

#define	PNG_FILTER_NONE		0
#define	PNG_FILTER_SUB		1
#define	PNG_FILTER_UP		2
#define	PNG_FILTER_AVG		3
#define	PNG_FILTER_PAETH	4

    switch (*thisLine) {
    case PNG_FILTER_NONE:	/* Nothing to do */
	break;
    case PNG_FILTER_SUB: {	/* Sub(x) = Raw(x) - Raw(x-bpp) */
	unsigned char *rawBpp = thisLine + 1;
	unsigned char *raw = rawBpp + pngPtr->bytesPerPixel;
	unsigned char *end = thisLine + pngPtr->phaseSize;

	while (raw < end) {
	    *raw++ += *rawBpp++;
	}
	break;
    }
    case PNG_FILTER_UP:		/* Up(x) = Raw(x) - Prior(x) */
	if (pngPtr->currentLine > startLine[pngPtr->phase]) {
	    unsigned char *prior = lastLine + 1;
	    unsigned char *raw = thisLine + 1;
	    unsigned char *end = thisLine + pngPtr->phaseSize;

	    while (raw < end) {
		*raw++ += *prior++;
	    }
	}
	break;
    case PNG_FILTER_AVG:
	/* Avg(x) = Raw(x) - floor((Raw(x-bpp)+Prior(x))/2) */
	if (pngPtr->currentLine > startLine[pngPtr->phase]) {
	    unsigned char *prior = lastLine + 1;
	    unsigned char *rawBpp = thisLine + 1;
	    unsigned char *raw = rawBpp;
	    unsigned char *end = thisLine + pngPtr->phaseSize;
	    unsigned char *end2 = raw + pngPtr->bytesPerPixel;

	    while ((raw < end2) && (raw < end)) {
		*raw++ += *prior++ / 2;
	    }

	    while (raw < end) {
		*raw++ += (unsigned char)
			(((int) *rawBpp++ + (int) *prior++) / 2);
	    }
	} else {
	    unsigned char *rawBpp = thisLine + 1;
	    unsigned char *raw = rawBpp + pngPtr->bytesPerPixel;
	    unsigned char *end = thisLine + pngPtr->phaseSize;

	    while (raw < end) {
		*raw++ += *rawBpp++ / 2;
	    }
	}
	break;
    case PNG_FILTER_PAETH:
	/* Paeth(x) = Raw(x) - PaethPredictor(Raw(x-bpp), Prior(x), Prior(x-bpp)) */
	if (pngPtr->currentLine > startLine[pngPtr->phase]) {
	    unsigned char *priorBpp = lastLine + 1;
	    unsigned char *prior = priorBpp;
	    unsigned char *rawBpp = thisLine + 1;
	    unsigned char *raw = rawBpp;
	    unsigned char *end = thisLine + pngPtr->phaseSize;
	    unsigned char *end2 = rawBpp + pngPtr->bytesPerPixel;

	    while ((raw < end) && (raw < end2)) {
		*raw++ += *prior++;
	    }

	    while (raw < end) {
		*raw++ += Paeth(*rawBpp++, *prior++, *priorBpp++);
	    }
	} else {
	    unsigned char *rawBpp = thisLine + 1;
	    unsigned char *raw = rawBpp + pngPtr->bytesPerPixel;
	    unsigned char *end = thisLine + pngPtr->phaseSize;

	    while (raw < end) {
		*raw++ += *rawBpp++;
	    }
	}
	break;
    default:
	Tcl_SetResult(interp, "Invalid filter type", TCL_STATIC);
	return TCL_ERROR;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * DecodeLine --
 *
 *	Unfilters a line of pixels from the PNG source data and decodes the
 *	data into the Tk_PhotoImageBlock for later copying into the Tk image.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if the filter type is not recognized.
 *
 * Side effects:
 *	Pixel data in thisLine and block are modified and state information
 *	updated.
 *
 *----------------------------------------------------------------------
 */

static int
DecodeLine(
    Tcl_Interp *interp,
    PNGImage *pngPtr)
{
    unsigned char *pixelPtr = pngPtr->block.pixelPtr;
    int colNum = 0;		/* Current pixel column */
    unsigned char chan = 0;	/* Current channel (0..3) = (R, G, B, A) */
    unsigned char readByte = 0;	/* Current scan line byte */
    int haveBits = 0;		/* Number of bits remaining in current byte */
    unsigned char pixBits = 0;	/* Extracted bits for current channel */
    int shifts = 0;		/* Number of channels extracted from byte */
    int offset = 0;		/* Current offset into pixelPtr */
    int colStep = 1;		/* Column increment each pass */
    int pixStep = 0;		/* extra pixelPtr increment each pass */
    unsigned char lastPixel[6];
    unsigned char *p = Tcl_GetByteArrayFromObj(pngPtr->thisLineObj, NULL);

    p++;
    if (UnfilterLine(interp, pngPtr) == TCL_ERROR) {
	return TCL_ERROR;
    }

    if (pngPtr->interlace) {
	switch (pngPtr->phase) {
	case 1:			/* Phase 1: */
	    colStep = 8;	/* 1 pixel per block of 8 per line */
	    break;		/* Start at column 0 */
	case 2:			/* Phase 2: */
	    colStep = 8;	/* 1 pixels per block of 8 per line */
	    colNum = 4;		/* Start at column 4 */
	    break;
	case 3:			/* Phase 3: */
	    colStep = 4;	/* 2 pixels per block of 8 per line */
	    break;		/* Start at column 0 */
	case 4:			/* Phase 4: */
	    colStep = 4;	/* 2 pixels per block of 8 per line */
	    colNum = 2;		/* Start at column 2 */
	    break;
	case 5:			/* Phase 5: */
	    colStep = 2;	/* 4 pixels per block of 8 per line */
	    break;		/* Start at column 0 */
	case 6:			/* Phase 6: */
	    colStep = 2;	/* 4 pixels per block of 8 per line */
	    colNum = 1;		/* Start at column 1 */
	    break;
				/* Phase 7: */
				/* 8 pixels per block of 8 per line */
				/* Start at column 0 */
	}
    }

    /*
     * Calculate offset into pixelPtr for the first pixel of the line.
     */

    offset = pngPtr->currentLine * pngPtr->block.pitch;

    /*
     * Adjust up for the starting pixel of the line.
     */

    offset += colNum * pngPtr->block.pixelSize;

    /*
     * Calculate the extra number of bytes to skip between columns.
     */

    pixStep = (colStep - 1) * pngPtr->block.pixelSize;

    for ( ; colNum < pngPtr->block.width ; colNum += colStep) {
	if (haveBits < (pngPtr->bitDepth * pngPtr->numChannels)) {
	    haveBits = 0;
	}

	for (chan = 0 ; chan < pngPtr->numChannels ; chan++) {
	    if (!haveBits) {
		shifts = 0;
		readByte = *p++;
		haveBits += 8;
	    }

	    if (16 == pngPtr->bitDepth) {
		pngPtr->block.pixelPtr[offset++] = readByte;

		if (pngPtr->useTRNS) {
		    lastPixel[chan * 2] = readByte;
		}

		readByte = *p++;

		if (pngPtr->useTRNS) {
		    lastPixel[(chan * 2) + 1] = readByte;
		}

		pngPtr->block.pixelPtr[offset++] = readByte;

		haveBits = 0;
		continue;
	    }

	    switch (pngPtr->bitDepth) {
	    case 1:
		pixBits = (unsigned char)((readByte >> (7-shifts)) & 0x01);
		break;
	    case 2:
		pixBits = (unsigned char)((readByte >> (6-shifts*2)) & 0x03);
		break;
	    case 4:
		pixBits = (unsigned char)((readByte >> (4-shifts*4)) & 0x0f);
		break;
	    case 8:
		pixBits = readByte;
		break;
	    }

	    if (PNG_COLOR_PLTE == pngPtr->colorType) {
		pixelPtr[offset++] = pngPtr->palette[pixBits].red;
		pixelPtr[offset++] = pngPtr->palette[pixBits].green;
		pixelPtr[offset++] = pngPtr->palette[pixBits].blue;
		pixelPtr[offset++] = pngPtr->palette[pixBits].alpha;
		chan += 2;
	    } else {
		pixelPtr[offset++] = (unsigned char)
			(pixBits * pngPtr->bitScale);

		if (pngPtr->useTRNS) {
		    lastPixel[chan] = pixBits;
		}
	    }

	    haveBits -= pngPtr->bitDepth;
	    shifts++;
	}

	/*
	 * Apply boolean transparency via tRNS data if necessary (where
	 * necessary means a tRNS chunk was provided and we're not using an
	 * alpha channel or indexed alpha).
	 */

	if ((PNG_COLOR_PLTE != pngPtr->colorType) &&
		((pngPtr->colorType & PNG_COLOR_ALPHA) == 0)) {
	    unsigned char alpha;

	    if (pngPtr->useTRNS) {
		if (memcmp(lastPixel, pngPtr->transVal,
			pngPtr->bytesPerPixel) == 0) {
		    alpha = 0x00;
		} else {
		    alpha = 0xff;
		}
	    } else {
		alpha = 0xff;
	    }

	    pixelPtr[offset++] = alpha;

	    if (16 == pngPtr->bitDepth) {
		pixelPtr[offset++] = alpha;
	    }
	}

	offset += pixStep;
    }

    if (pngPtr->interlace) {
	/* Skip lines */

	switch (pngPtr->phase) {
	case 1: case 2: case 3:
	    pngPtr->currentLine += 8;
	    break;
	case 4: case 5:
	    pngPtr->currentLine += 4;
	    break;
	case 6: case 7:
	    pngPtr->currentLine += 2;
	    break;
	}

	/*
	 * Start the next phase if there are no more lines to do.
	 */

	if (pngPtr->currentLine >= pngPtr->block.height) {
	    unsigned long pixels = 0;

	    while ((!pixels || (pngPtr->currentLine >= pngPtr->block.height))
		    && (pngPtr->phase < 7)) {
		pngPtr->phase++;

		switch (pngPtr->phase) {
		case 2:
		    pixels = (pngPtr->block.width + 3) >> 3;
		    pngPtr->currentLine = 0;
		    break;
		case 3:
		    pixels = (pngPtr->block.width + 3) >> 2;
		    pngPtr->currentLine = 4;
		    break;
		case 4:
		    pixels = (pngPtr->block.width + 1) >> 2;
		    pngPtr->currentLine = 0;
		    break;
		case 5:
		    pixels = (pngPtr->block.width + 1) >> 1;
		    pngPtr->currentLine = 2;
		    break;
		case 6:
		    pixels = pngPtr->block.width >> 1;
		    pngPtr->currentLine = 0;
		    break;
		case 7:
		    pngPtr->currentLine = 1;
		    pixels = pngPtr->block.width;
		    break;
		}
	    }

	    if (16 == pngPtr->bitDepth) {
		pngPtr->phaseSize = 1 + (pngPtr->numChannels * pixels * 2);
	    } else {
		pngPtr->phaseSize = 1 + ((pngPtr->numChannels * pixels *
			pngPtr->bitDepth + 7) >> 3);
	    }
	}
    } else {
	pngPtr->currentLine++;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ReadIDAT --
 *
 *	This function reads the IDAT (pixel data) chunk from the PNG file to
 *	build the image. It will continue reading until all IDAT chunks have
 *	been processed or an error occurs.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error occurs or an IDAT chunk is
 *	invalid.
 *
 * Side effects:
 *	The access position in f advances. Memory may be allocated by zlib
 *	through PNGZAlloc.
 *
 *----------------------------------------------------------------------
 */

static int
ReadIDAT(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    int chunkSz,
    unsigned long crc)
{
    /*
     * Process IDAT contents until there is no more in this chunk.
     */

    while (chunkSz && !Tcl_ZlibStreamEof(pngPtr->stream)) {
	int len1, len2;

	/*
	 * Read another block of input into the zlib stream if data remains.
	 */

	if (chunkSz) {
	    Tcl_Obj *inputObj = NULL;
	    int blockSz = PNG_MIN(chunkSz, PNG_BLOCK_SZ);
	    unsigned char *inputPtr = NULL;

	    /*
	     * Check for end of zlib stream.
	     */

	    if (Tcl_ZlibStreamEof(pngPtr->stream)) {
		Tcl_SetResult(interp, "Extra data after end of zlib stream",
			TCL_STATIC);
		return TCL_ERROR;
	    }

	    inputObj = Tcl_NewObj();
	    Tcl_IncrRefCount(inputObj);
	    inputPtr = Tcl_SetByteArrayLength(inputObj, blockSz);

	    /*
	     * Read the next bit of IDAT chunk data, up to read buffer size.
	     */

	    if (ReadData(interp, pngPtr, inputPtr, blockSz,
		    &crc) == TCL_ERROR) {
		Tcl_DecrRefCount(inputObj);
		return TCL_ERROR;
	    }

	    chunkSz -= blockSz;

	    Tcl_ZlibStreamPut(pngPtr->stream, inputObj, TCL_ZLIB_NO_FLUSH);
	    Tcl_DecrRefCount(inputObj);
	}

	/*
	 * Inflate, processing each output buffer's worth as a line of pixels,
	 * until we cannot fill the buffer any more.
	 */

    getNextLine:
	Tcl_GetByteArrayFromObj(pngPtr->thisLineObj, &len1);
	if (Tcl_ZlibStreamGet(pngPtr->stream, pngPtr->thisLineObj,
		pngPtr->phaseSize - len1) == TCL_ERROR) {
	    return TCL_ERROR;
	}
	Tcl_GetByteArrayFromObj(pngPtr->thisLineObj, &len2);

	if (len2 == pngPtr->phaseSize) {
	    if (pngPtr->phase > 7) {
		Tcl_SetResult(interp,
			"Extra data after final scan line of final phase",
			TCL_STATIC);
		return TCL_ERROR;
	    }

	    if (DecodeLine(interp, pngPtr) == TCL_ERROR) {
		return TCL_ERROR;
	    }

	    /*
	     * Swap the current/last lines so that we always have the last
	     * line processed available, which is necessary for filtering.
	     */

	    {
		Tcl_Obj *temp = pngPtr->lastLineObj;

		pngPtr->lastLineObj = pngPtr->thisLineObj;
		pngPtr->thisLineObj = temp;
	    }
	    Tcl_SetByteArrayLength(pngPtr->thisLineObj, 0);

	    /*
	     * Try to read another line of pixels out of the buffer
	     * immediately.
	     */

	    goto getNextLine;
	}

	/*
	 * Got less than a whole buffer-load of pixels. Either we're going to
	 * be getting more data from the next IDAT, or we've done what we can
	 * here.
	 */
    }

    /*
     * Ensure that if we've got to the end of the compressed data, we've
     * also got to the end of the compressed stream. This sanity check is
     * enforced by most PNG readers.
     */

    if (chunkSz != 0) {
	Tcl_AppendResult(interp,
		"compressed data after stream finalize in PNG data", NULL);
	return TCL_ERROR;
    }

    return CheckCRC(interp, pngPtr, crc);
}

/*
 *----------------------------------------------------------------------
 *
 * ApplyAlpha --
 *
 *	Applies an overall alpha value to a complete image that has been read.
 *	This alpha value is specified using the -format option to [image
 *	create photo].
 *
 * Results:
 *	N/A
 *
 * Side effects:
 *	The access position in f may change.
 *
 *----------------------------------------------------------------------
 */

static void
ApplyAlpha(
    PNGImage *pngPtr)
{
    if (pngPtr->alpha != 1.0) {
	register unsigned char *p = pngPtr->block.pixelPtr;
	unsigned char *endPtr = p + pngPtr->blockLen;
	int offset = pngPtr->block.offset[3];

	p += offset;

	if (16 == pngPtr->bitDepth) {
	    register int channel;

	    while (p < endPtr) {
		channel = (unsigned char)
			(((p[0] << 8) | p[1]) * pngPtr->alpha);

		*p++ = (unsigned char) (channel >> 8);
		*p++ = (unsigned char) (channel & 0xff);

		p += offset;
	    }
	} else {
	    while (p < endPtr) {
		p[0] = (unsigned char) (pngPtr->alpha * p[0]);
		p += 1 + offset;
	    }
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * ParseFormat --
 *
 *	This function parses the -format string that can be specified to the
 *	[image create photo] command to extract options for postprocessing of
 *	loaded images. Currently, this just allows specifying and applying an
 *	overall alpha value to the loaded image (for example, to make it
 *	entirely 50% as transparent as the actual image file).
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if the format specification is invalid.
 *
 * Side effects:
 *	None
 *
 *----------------------------------------------------------------------
 */

static int
ParseFormat(
    Tcl_Interp *interp,
    Tcl_Obj *fmtObj,
    PNGImage *pngPtr)
{
    Tcl_Obj **objv = NULL;
    int objc = 0;
    static const char *const fmtOptions[] = {
	"png", "-alpha", NULL
    };
    enum fmtOptions {
	OPT_PNG, OPT_ALPHA
    };

    /*
     * Extract elements of format specification as a list.
     */

    if (fmtObj &&
	    Tcl_ListObjGetElements(interp, fmtObj, &objc, &objv) != TCL_OK) {
	return TCL_ERROR;
    }

    for (; objc>0 ; objc--, objv++) {
    	int optIndex;

        if (Tcl_GetIndexFromObj(interp, objv[0], fmtOptions, "option", 0,
		&optIndex) == TCL_ERROR) {
            return TCL_ERROR;
	}

	/*
	 * Ignore the "png" part of the format specification.
	 */

	if (OPT_PNG == optIndex) {
	    continue;
	}

    	if (objc < 2) {
	    Tcl_WrongNumArgs(interp, 1, objv, "value");
	    return TCL_ERROR;
    	}

	objc--;
	objv++;

	switch ((enum fmtOptions) optIndex) {
	case OPT_PNG:
	    break;

	case OPT_ALPHA:
	    if (Tcl_GetDoubleFromObj(interp, objv[0],
		    &pngPtr->alpha) == TCL_ERROR) {
		return TCL_ERROR;
	    }

	    if ((pngPtr->alpha < 0.0) || (pngPtr->alpha > 1.0)) {
		Tcl_SetResult(interp,
			"-alpha value must be between 0.0 and 1.0",
			TCL_STATIC);
		return TCL_ERROR;
	    }
	    break;
	}
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * DecodePNG --
 *
 *	This function handles the entirety of reading a PNG file (or data)
 *	from the first byte to the last.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O error occurs or any problems are
 *	detected in the PNG file.
 *
 * Side effects:
 *	The access position in f advances. Memory may be allocated and image
 *	dimensions and contents may change.
 *
 *----------------------------------------------------------------------
 */

static int
DecodePNG(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    Tcl_Obj *fmtObj,
    Tk_PhotoHandle imageHandle,
    int destX,
    int destY)
{
    unsigned long chunkType;
    int chunkSz;
    unsigned long crc;

    /*
     * Parse the PNG signature and IHDR (header) chunk.
     */

    if (ReadIHDR(interp, pngPtr) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Extract alpha value from -format object, if specified.
     */

    if (ParseFormat(interp, fmtObj, pngPtr) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * The next chunk may either be a PLTE (Palette) chunk or the first of at
     * least one IDAT (data) chunks. It could also be one of a number of
     * ancillary chunks, but those are skipped for us by the switch in
     * ReadChunkHeader().
     *
     * PLTE is mandatory for color type 3 and forbidden for 2 and 6
     */

    if (ReadChunkHeader(interp, pngPtr, &chunkSz, &chunkType,
	    &crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    if (CHUNK_PLTE == chunkType) {
	/*
	 * Finish parsing the PLTE chunk.
	 */

	if (ReadPLTE(interp, pngPtr, chunkSz, crc) == TCL_ERROR) {
	    return TCL_ERROR;
	}

	/*
	 * Begin the next chunk.
	 */

	if (ReadChunkHeader(interp, pngPtr, &chunkSz, &chunkType,
		&crc) == TCL_ERROR) {
	    return TCL_ERROR;
	}
    } else if (PNG_COLOR_PLTE == pngPtr->colorType) {
	Tcl_SetResult(interp, "PLTE chunk required for indexed color",
		TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * The next chunk may be a tRNS (palette transparency) chunk, depending on
     * the color type. It must come after the PLTE chunk and before the IDAT
     * chunk, but can be present if there is no PLTE chunk because it can be
     * used for Grayscale and TrueColor in lieu of an alpha channel.
     */

    if (CHUNK_tRNS == chunkType) {
	/*
	 * Finish parsing the tRNS chunk.
	 */

	if (ReadTRNS(interp, pngPtr, chunkSz, crc) == TCL_ERROR) {
	    return TCL_ERROR;
	}

	/*
	 * Begin the next chunk.
	 */

	if (ReadChunkHeader(interp, pngPtr, &chunkSz, &chunkType,
		&crc) == TCL_ERROR) {
	    return TCL_ERROR;
	}
    }

    /*
     * Other ancillary chunk types could appear here, but for now we're only
     * interested in IDAT. The others should have been skipped.
     */

    if (CHUNK_IDAT != chunkType) {
	Tcl_SetResult(interp, "At least one IDAT chunk is required",
		TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * Expand the photo size (if not set by the user) to provide enough space
     * for the image being parsed. It does not matter if width or height wrap
     * to negative here: Tk will not shrink the image.
     */

    if (Tk_PhotoExpand(interp, imageHandle, destX + pngPtr->block.width,
	    destY + pngPtr->block.height) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * A scan line consists of one byte for a filter type, plus the number of
     * bits per color sample times the number of color samples per pixel.
     */

    if (pngPtr->block.width > ((INT_MAX - 1) / (pngPtr->numChannels * 2))) {
	Tcl_SetResult(interp,
		"Line size is out of supported range on this architecture",
		TCL_STATIC);
	return TCL_ERROR;
    }

    if (16 == pngPtr->bitDepth) {
	pngPtr->lineSize = 1 + (pngPtr->numChannels * pngPtr->block.width*2);
    } else {
	pngPtr->lineSize = 1 + ((pngPtr->numChannels * pngPtr->block.width) /
		(8 / pngPtr->bitDepth));
	if (pngPtr->block.width % (8 / pngPtr->bitDepth)) {
	    pngPtr->lineSize++;
	}
    }

    /*
     * Allocate space for decoding the scan lines.
     */

    pngPtr->lastLineObj = Tcl_NewObj();
    Tcl_IncrRefCount(pngPtr->lastLineObj);
    pngPtr->thisLineObj = Tcl_NewObj();
    Tcl_IncrRefCount(pngPtr->thisLineObj);

    pngPtr->block.pixelPtr = attemptckalloc(pngPtr->blockLen);
    if (!pngPtr->block.pixelPtr) {
	Tcl_SetResult(interp, "Memory allocation failed", TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * Determine size of the first phase if interlaced. Phase size should
     * always be <= line size, so probably not necessary to check for
     * arithmetic overflow here: should be covered by line size check.
     */

    if (pngPtr->interlace) {
	/*
	 * Only one pixel per block of 8 per line in the first phase.
	 */

	unsigned int pixels = (pngPtr->block.width + 7) >> 3;

	pngPtr->phase = 1;
	if (16 == pngPtr->bitDepth) {
	    pngPtr->phaseSize = 1 + pngPtr->numChannels*pixels*2;
	} else {
	    pngPtr->phaseSize = 1 +
		    ((pngPtr->numChannels*pixels*pngPtr->bitDepth + 7) >> 3);
	}
    } else {
	pngPtr->phaseSize = pngPtr->lineSize;
    }

    /*
     * All of the IDAT (data) chunks must be consecutive.
     */

    while (CHUNK_IDAT == chunkType) {
	if (ReadIDAT(interp, pngPtr, chunkSz, crc) == TCL_ERROR) {
	    return TCL_ERROR;
	}

	if (ReadChunkHeader(interp, pngPtr, &chunkSz, &chunkType,
		&crc) == TCL_ERROR) {
	    return TCL_ERROR;
	}
    }

    /*
     * Ensure that we've got to the end of the compressed stream now that
     * there are no more IDAT segments. This sanity check is enforced by most
     * PNG readers.
     */

    if (!Tcl_ZlibStreamEof(pngPtr->stream)) {
	Tcl_AppendResult(interp, "unfinalized data stream in PNG data", NULL);
	return TCL_ERROR;
    }

    /*
     * Now skip the remaining chunks which we're also not interested in.
     */

    while (CHUNK_IEND != chunkType) {
	if (SkipChunk(interp, pngPtr, chunkSz, crc) == TCL_ERROR) {
	    return TCL_ERROR;
	}

	if (ReadChunkHeader(interp, pngPtr, &chunkSz, &chunkType,
		&crc) == TCL_ERROR) {
	    return TCL_ERROR;
	}
    }

    /*
     * Got the IEND (end of image) chunk. Do some final checks...
     */

    if (chunkSz) {
	Tcl_SetResult(interp, "IEND chunk contents must be empty",
		TCL_STATIC);
	return TCL_ERROR;
    }

    /*
     * Check the CRC on the IEND chunk.
     */

    if (CheckCRC(interp, pngPtr, crc) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * TODO: verify that nothing else comes after the IEND chunk, or do we
     * really care?
     */

#if 0
    if (ReadData(interp, pngPtr, &c, 1, NULL) != TCL_ERROR) {
	Tcl_SetResult(interp, "Extra data following IEND chunk", TCL_STATIC);
	return TCL_ERROR;
    }
#endif

    /*
     * Apply overall image alpha if specified.
     */

    ApplyAlpha(pngPtr);

    /*
     * Copy the decoded image block into the Tk photo image.
     */

    if (Tk_PhotoPutBlock(interp, imageHandle, &pngPtr->block, destX, destY,
	    pngPtr->block.width, pngPtr->block.height,
	    TK_PHOTO_COMPOSITE_SET) == TCL_ERROR) {
	return TCL_ERROR;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * FileMatchPNG --
 *
 *	This function is invoked by the photo image type to see if a file
 *	contains image data in PNG format.
 *
 * Results:
 *	The return value is 1 if the first characters in file f look like PNG
 *	data, and 0 otherwise.
 *
 * Side effects:
 *	The access position in f may change.
 *
 *----------------------------------------------------------------------
 */

static int
FileMatchPNG(
    Tcl_Channel chan,
    const char *fileName,
    Tcl_Obj *fmtObj,
    int *widthPtr,
    int *heightPtr,
    Tcl_Interp *interp)
{
    PNGImage png;
    int match = 0;
    Tcl_SavedResult sya;

    Tcl_SaveResult(interp, &sya);

    InitPNGImage(interp, &png, chan, NULL, TCL_ZLIB_STREAM_INFLATE);

    if (ReadIHDR(interp, &png) == TCL_OK) {
	*widthPtr = png.block.width;
	*heightPtr = png.block.height;
	match = 1;
    }

    CleanupPNGImage(&png);
    Tcl_RestoreResult(interp, &sya);

    return match;
}

/*
 *----------------------------------------------------------------------
 *
 * FileReadPNG --
 *
 *	This function is called by the photo image type to read PNG format
 *	data from a file and write it into a given photo image.
 *
 * Results:
 *	A standard TCL completion code. If TCL_ERROR is returned then an error
 *	message is left in the interp's result.
 *
 * Side effects:
 *	The access position in file f is changed, and new data is added to the
 *	image given by imageHandle.
 *
 *----------------------------------------------------------------------
 */

static int
FileReadPNG(
    Tcl_Interp *interp,
    Tcl_Channel chan,
    const char *fileName,
    Tcl_Obj *fmtObj,
    Tk_PhotoHandle imageHandle,
    int destX,
    int destY,
    int width,
    int height,
    int srcX,
    int srcY)
{
    PNGImage png;
    int result = TCL_ERROR;

    result = InitPNGImage(interp, &png, chan, NULL, TCL_ZLIB_STREAM_INFLATE);

    if (TCL_OK == result) {
	result = DecodePNG(interp, &png, fmtObj, imageHandle, destX, destY);
    }

    CleanupPNGImage(&png);
    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * StringMatchPNG --
 *
 *	This function is invoked by the photo image type to see if an object
 *	contains image data in PNG format.
 *
 * Results:
 *	The return value is 1 if the first characters in the data are like PNG
 *	data, and 0 otherwise.
 *
 * Side effects:
 *	The size of the image is placed in widthPre and heightPtr.
 *
 *----------------------------------------------------------------------
 */

static int
StringMatchPNG(
    Tcl_Obj *pObjData,
    Tcl_Obj *fmtObj,
    int *widthPtr,
    int *heightPtr,
    Tcl_Interp *interp)
{
    PNGImage png;
    int match = 0;
    Tcl_SavedResult sya;

    Tcl_SaveResult(interp, &sya);
    InitPNGImage(interp, &png, NULL, pObjData, TCL_ZLIB_STREAM_INFLATE);

    png.strDataBuf = Tcl_GetByteArrayFromObj(pObjData, &png.strDataLen);

    if (ReadIHDR(interp, &png) == TCL_OK) {
	*widthPtr = png.block.width;
	*heightPtr = png.block.height;
	match = 1;
    }

    CleanupPNGImage(&png);
    Tcl_RestoreResult(interp, &sya);
    return match;
}

/*
 *----------------------------------------------------------------------
 *
 * StringReadPNG --
 *
 *	This function is called by the photo image type to read PNG format
 *	data from an object and give it to the photo image.
 *
 * Results:
 *	A standard TCL completion code. If TCL_ERROR is returned then an error
 *	message is left in the interp's result.
 *
 * Side effects:
 *	New data is added to the image given by imageHandle.
 *
 *----------------------------------------------------------------------
 */

static int
StringReadPNG(
    Tcl_Interp *interp,
    Tcl_Obj *pObjData,
    Tcl_Obj *fmtObj,
    Tk_PhotoHandle imageHandle,
    int destX,
    int destY,
    int width,
    int height,
    int srcX,
    int srcY)
{
    PNGImage png;
    int result = TCL_ERROR;

    result = InitPNGImage(interp, &png, NULL, pObjData,
	    TCL_ZLIB_STREAM_INFLATE);

    if (TCL_OK == result) {
	result = DecodePNG(interp, &png, fmtObj, imageHandle, destX, destY);
    }

    CleanupPNGImage(&png);
    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * WriteData --
 *
 *	This function writes a bytes from a buffer out to the PNG image.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if the write fails.
 *
 * Side effects:
 *	File or buffer will be modified.
 *
 *----------------------------------------------------------------------
 */

static int
WriteData(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    const unsigned char *srcPtr,
    int srcSz,
    unsigned long *crcPtr)
{
    if (!srcPtr || !srcSz) {
	return TCL_OK;
    }

    if (crcPtr) {
	*crcPtr = Tcl_ZlibCRC32(*crcPtr, srcPtr, srcSz);
    }

    /*
     * TODO: is Tcl_AppendObjToObj faster here? i.e., does Tcl join the
     * objects immediately or store them in a multi-object rep?
     */

    if (pngPtr->objDataPtr) {
	int objSz;
	unsigned char *destPtr;

	Tcl_GetByteArrayFromObj(pngPtr->objDataPtr, &objSz);

	if (objSz > INT_MAX - srcSz) {
	    Tcl_SetResult(interp,
		    "Image too large to store completely in byte array",
		    TCL_STATIC);
	    return TCL_ERROR;
	}

	destPtr = Tcl_SetByteArrayLength(pngPtr->objDataPtr, objSz + srcSz);

	if (!destPtr) {
	    Tcl_SetResult(interp, "Memory allocation failed", TCL_STATIC);
	    return TCL_ERROR;
	}

	memcpy(destPtr+objSz, srcPtr, srcSz);
    } else if (Tcl_Write(pngPtr->channel, (const char *) srcPtr, srcSz) < 0) {
	/* TODO: reason */

	Tcl_SetResult(interp, "Write to channel failed", TCL_STATIC);
	return TCL_ERROR;
    }

    return TCL_OK;
}

static inline int
WriteByte(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    unsigned char c,
    unsigned long *crcPtr)
{
    return WriteData(interp, pngPtr, &c, 1, crcPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * WriteInt32 --
 *
 *	This function writes a 32-bit integer value out to the PNG image as
 *	four bytes in network byte order.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if the write fails.
 *
 * Side effects:
 *	File or buffer will be modified.
 *
 *----------------------------------------------------------------------
 */

static inline int
WriteInt32(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    unsigned long l,
    unsigned long *crcPtr)
{
    unsigned char pc[4];

    pc[0] = (unsigned char) ((l & 0xff000000) >> 24);
    pc[1] = (unsigned char) ((l & 0x00ff0000) >> 16);
    pc[2] = (unsigned char) ((l & 0x0000ff00) >> 8);
    pc[3] = (unsigned char) ((l & 0x000000ff) >> 0);

    return WriteData(interp, pngPtr, pc, 4, crcPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * WriteChunk --
 *
 *	Writes a complete chunk to the PNG image, including chunk type,
 *	length, contents, and CRC.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if the write fails.
 *
 * Side effects:
 *	None
 *
 *----------------------------------------------------------------------
 */

static inline int
WriteChunk(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    unsigned long chunkType,
    const unsigned char *dataPtr,
    int dataSize)
{
    unsigned long crc = Tcl_ZlibCRC32(0, NULL, 0);
    int result = TCL_OK;

    /*
     * Write the length field for the chunk.
     */

    result = WriteInt32(interp, pngPtr, dataSize, NULL);

    /*
     * Write the Chunk Type.
     */

    if (TCL_OK == result) {
	result = WriteInt32(interp, pngPtr, chunkType, &crc);
    }

    /*
     * Write the contents (if any).
     */

    if (TCL_OK == result) {
	result = WriteData(interp, pngPtr, dataPtr, dataSize, &crc);
    }

    /*
     * Write out the CRC at the end of the chunk.
     */

    if (TCL_OK == result) {
	result = WriteInt32(interp, pngPtr, crc, NULL);
    }

    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * WriteIHDR --
 *
 *	This function writes the PNG header at the beginning of a PNG file,
 *	which includes information such as dimensions and color type.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if the write fails.
 *
 * Side effects:
 *	File or buffer will be modified.
 *
 *----------------------------------------------------------------------
 */

static int
WriteIHDR(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    Tk_PhotoImageBlock *blockPtr)
{
    unsigned long crc = Tcl_ZlibCRC32(0, NULL, 0);
    int result = TCL_OK;

    /*
     * The IHDR (header) chunk has a fixed size of 13 bytes.
     */

    result = WriteInt32(interp, pngPtr, 13, NULL);

    /*
     * Write the IHDR Chunk Type.
     */

    if (TCL_OK == result) {
	result = WriteInt32(interp, pngPtr, CHUNK_IHDR, &crc);
    }

    /*
     * Write the image width, height.
     */

    if (TCL_OK == result) {
	result = WriteInt32(interp, pngPtr, (unsigned long) blockPtr->width,
		&crc);
    }

    if (TCL_OK == result) {
	result = WriteInt32(interp, pngPtr, (unsigned long) blockPtr->height,
		&crc);
    }

    /*
     * Write bit depth. Although the PNG format supports 16 bits per channel,
     * Tk supports only 8 in the internal representation, which blockPtr
     * points to.
     */

    if (TCL_OK == result) {
	result = WriteByte(interp, pngPtr, 8, &crc);
    }

    /*
     * Write out the color type, previously determined.
     */

    if (TCL_OK == result) {
	result = WriteByte(interp, pngPtr, pngPtr->colorType, &crc);
    }

    /*
     * Write compression method (only one method is defined).
     */

    if (TCL_OK == result) {
	result = WriteByte(interp, pngPtr, PNG_COMPRESS_DEFLATE, &crc);
    }

    /*
     * Write filter method (only one method is defined).
     */

    if (TCL_OK == result) {
	result = WriteByte(interp, pngPtr, PNG_FILTMETH_STANDARD, &crc);
    }

    /*
     * Write interlace method as not interlaced.
     *
     * TODO: support interlace through -format?
     */

    if (TCL_OK == result) {
	result = WriteByte(interp, pngPtr, PNG_INTERLACE_NONE, &crc);
    }

    /*
     * Write out the CRC at the end of the chunk.
     */

    if (TCL_OK == result) {
	result = WriteInt32(interp, pngPtr, crc, NULL);
    }

    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * WriteIDAT --
 *
 *	Writes the IDAT (data) chunk to the PNG image, containing the pixel
 *	channel data. Currently, image lines are not filtered and writing
 *	interlaced pixels is not supported.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if the write fails.
 *
 * Side effects:
 *	None
 *
 *----------------------------------------------------------------------
 */

static int
WriteIDAT(
    Tcl_Interp *interp,
    PNGImage *pngPtr,
    Tk_PhotoImageBlock *blockPtr)
{
    int rowNum, flush = TCL_ZLIB_NO_FLUSH, outputSize, result;
    Tcl_Obj *outputObj;
    unsigned char *outputBytes;

    /*
     * Filter and compress each row one at a time.
     */

    for (rowNum=0 ; rowNum < blockPtr->height ; rowNum++) {
	int colNum;
	unsigned char *srcPtr, *destPtr;

	srcPtr = blockPtr->pixelPtr + (rowNum * blockPtr->pitch);
	destPtr = Tcl_SetByteArrayLength(pngPtr->thisLineObj,
		pngPtr->lineSize);

	/*
	 * TODO: use Paeth filtering.
	 */

	*destPtr++ = PNG_FILTER_NONE;

	/*
	 * Copy each pixel into the destination buffer after the filter type
	 * before filtering.
	 */

	for (colNum = 0 ; colNum < blockPtr->width ; colNum++) {
	    /*
	     * Copy red or gray channel.
	     */

	    *destPtr++ = srcPtr[blockPtr->offset[0]];

	    /* 
	     * If not grayscale, copy the green and blue channels.
	     */

	    if (pngPtr->colorType & PNG_COLOR_USED) {
		*destPtr++ = srcPtr[blockPtr->offset[1]];
		*destPtr++ = srcPtr[blockPtr->offset[2]];
	    }

	    /*
	     * Copy the alpha channel, if used.
	     */

	    if (pngPtr->colorType & PNG_COLOR_ALPHA) {
		*destPtr++ = srcPtr[blockPtr->offset[3]];
	    }

	    /*
	     * Point to the start of the next pixel.
	     */

	    srcPtr += blockPtr->pixelSize;
	}

	/*
	 * Compress the line of pixels into the destination. If this is the
	 * last line, finalize the compressor at the same time. Note that this
	 * can't be just a flush; that leads to a file that some PNG readers
	 * choke on. [Bug 2984787]
	 */

	if (rowNum + 1 == blockPtr->height) {
	    flush = TCL_ZLIB_FINALIZE;
	}
	if (Tcl_ZlibStreamPut(pngPtr->stream, pngPtr->thisLineObj,
		flush) != TCL_OK) {
	    Tcl_SetResult(interp, "deflate() returned error", TCL_STATIC);
	    return TCL_ERROR;
	}

	/*
	 * Swap line buffers to keep the last around for filtering next.
	 */

	{
	    Tcl_Obj *temp = pngPtr->lastLineObj;

	    pngPtr->lastLineObj = pngPtr->thisLineObj;
	    pngPtr->thisLineObj = temp;
	}
    }

    /*
     * Now get the compressed data and write it as one big IDAT chunk.
     */

    outputObj = Tcl_NewObj();
    (void) Tcl_ZlibStreamGet(pngPtr->stream, outputObj, -1);
    outputBytes = Tcl_GetByteArrayFromObj(outputObj, &outputSize);
    result = WriteChunk(interp, pngPtr, CHUNK_IDAT, outputBytes, outputSize);
    Tcl_DecrRefCount(outputObj);
    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * WriteExtraChunks --
 *
 *	Writes an sBIT and a tEXt chunks to the PNG image, describing a bunch
 *	of not very important metadata that many readers seem to need anyway.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if the write fails.
 *
 * Side effects:
 *	None
 *
 *----------------------------------------------------------------------
 */

static int
WriteExtraChunks(
    Tcl_Interp *interp,
    PNGImage *pngPtr)
{
    static const unsigned char sBIT_contents[] = {
	8, 8, 8, 8
    };
    int sBIT_length = 4;
    Tcl_DString buf;

    /*
     * Each byte of each channel is always significant; we always write RGBA
     * images with 8 bits per channel as that is what the photo image's basic
     * data model is.
     */

    switch (pngPtr->colorType) {
    case PNG_COLOR_GRAY:
	sBIT_length = 1;
	break;
    case PNG_COLOR_GRAYALPHA:
	sBIT_length = 2;
	break;
    case PNG_COLOR_RGB:
    case PNG_COLOR_PLTE:
	sBIT_length = 3;
	break;
    case PNG_COLOR_RGBA:
	sBIT_length = 4;
	break;
    }
    if (WriteChunk(interp, pngPtr, CHUNK_sBIT, sBIT_contents, sBIT_length)
	    != TCL_OK) {
	return TCL_ERROR;
    }

    /*
     * Say that it is Tk that made the PNG. Note that we *need* the NUL at the
     * end of "Software" to be transferred; do *not* change the length
     * parameter to -1 there!
     */

    Tcl_DStringInit(&buf);
    Tcl_DStringAppend(&buf, "Software", 9);
    Tcl_DStringAppend(&buf, "Tk Toolkit v", -1);
    Tcl_DStringAppend(&buf, TK_PATCH_LEVEL, -1);
    if (WriteChunk(interp, pngPtr, CHUNK_tEXt,
	    (unsigned char *) Tcl_DStringValue(&buf),
	    Tcl_DStringLength(&buf)) != TCL_OK) {
	Tcl_DStringFree(&buf);
	return TCL_ERROR;
    }
    Tcl_DStringFree(&buf);

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * EncodePNG --
 *
 *	This function handles the entirety of writing a PNG file (or data)
 *	from the first byte to the last. No effort is made to optimize the
 *	image data for best compression.
 *
 * Results:
 *	TCL_OK, or TCL_ERROR if an I/O or memory error occurs.
 *
 * Side effects:
 *	None
 *
 *----------------------------------------------------------------------
 */

static int
EncodePNG(
    Tcl_Interp *interp,
    Tk_PhotoImageBlock *blockPtr,
    PNGImage *pngPtr)
{
    int greenOffset, blueOffset, alphaOffset;

    /*
     * Determine appropriate color type based on color usage (e.g., only red
     * and maybe alpha channel = grayscale).
     *
     * TODO: Check whether this is doing any good; Tk might just be pushing
     * full RGBA data all the time through here, even though the actual image
     * doesn't need it...
     */

    greenOffset = blockPtr->offset[1] - blockPtr->offset[0];
    blueOffset = blockPtr->offset[2] - blockPtr->offset[0];
    alphaOffset = blockPtr->offset[3];
    if ((alphaOffset >= blockPtr->pixelSize) || (alphaOffset < 0)) {
	alphaOffset = 0;
    } else {
	alphaOffset -= blockPtr->offset[0];
    }

    if ((greenOffset != 0) || (blueOffset != 0)) {
	if (alphaOffset) {
	    pngPtr->colorType = PNG_COLOR_RGBA;
	    pngPtr->bytesPerPixel = 4;
	} else {
	    pngPtr->colorType = PNG_COLOR_RGBA;
	    pngPtr->bytesPerPixel = 3;
	}
    } else {
	if (alphaOffset) {
	    pngPtr->colorType = PNG_COLOR_GRAYALPHA;
	    pngPtr->bytesPerPixel = 2;
	} else {
	    pngPtr->colorType = PNG_COLOR_GRAY;
	    pngPtr->bytesPerPixel = 1;
	}
    }

    /*
     * Allocate buffers for lines for filtering and compressed data.
     */

    pngPtr->lineSize = 1 + (pngPtr->bytesPerPixel * blockPtr->width);
    pngPtr->blockLen = pngPtr->lineSize * blockPtr->height;

    if ((blockPtr->width > (INT_MAX - 1) / (pngPtr->bytesPerPixel)) ||
	    (blockPtr->height > INT_MAX / pngPtr->lineSize)) {
	Tcl_SetResult(interp, "Image is too large to encode pixel data",
		TCL_STATIC);
	return TCL_ERROR;
    }

    pngPtr->lastLineObj = Tcl_NewObj();
    Tcl_IncrRefCount(pngPtr->lastLineObj);
    pngPtr->thisLineObj = Tcl_NewObj();
    Tcl_IncrRefCount(pngPtr->thisLineObj);

    /*
     * Write out the PNG Signature that all PNGs begin with.
     */

    if (WriteData(interp, pngPtr, pngSignature, PNG_SIG_SZ,
	    NULL) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Write out the IHDR (header) chunk containing image dimensions, color
     * type, etc.
     */

    if (WriteIHDR(interp, pngPtr, blockPtr) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Write out the extra chunks containing metadata that is of interest to
     * other programs more than us.
     */

    if (WriteExtraChunks(interp, pngPtr) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Write out the image pixels in the IDAT (data) chunk.
     */

    if (WriteIDAT(interp, pngPtr, blockPtr) == TCL_ERROR) {
	return TCL_ERROR;
    }

    /*
     * Write out the IEND chunk that all PNGs end with.
     */

    return WriteChunk(interp, pngPtr, CHUNK_IEND, NULL, 0);
}

/*
 *----------------------------------------------------------------------
 *
 * FileWritePNG --
 *
 *	This function is called by the photo image type to write PNG format
 *	data to a file.
 *
 * Results:
 *	A standard TCL completion code. If TCL_ERROR is returned then an error
 *	message is left in the interp's result.
 *
 * Side effects:
 *	The specified file is overwritten.
 *
 *----------------------------------------------------------------------
 */

static int
FileWritePNG(
    Tcl_Interp *interp,
    const char *filename,
    Tcl_Obj *fmtObj,
    Tk_PhotoImageBlock *blockPtr)
{
    Tcl_Channel chan;
    PNGImage png;
    int result = TCL_ERROR;

    /*
     * Open a Tcl file channel where the image data will be stored. Tk ought
     * to take care of this, and just provide a channel, but it doesn't.
     */

    chan = Tcl_OpenFileChannel(interp, filename, "w", 0644);

    if (!chan) {
	return TCL_ERROR;
    }

    /*
     * Initalize PNGImage instance for encoding.
     */

    if (InitPNGImage(interp, &png, chan, NULL,
	    TCL_ZLIB_STREAM_DEFLATE) == TCL_ERROR) {
	goto cleanup;
    }

    /*
     * Set the translation mode to binary so that CR and LF are not to the
     * platform's EOL sequence.
     */

    if (Tcl_SetChannelOption(interp, chan, "-translation",
	    "binary") != TCL_OK) {
	goto cleanup;
    }

    /*
     * Write the raw PNG data out to the file.
     */

    result = EncodePNG(interp, blockPtr, &png);

  cleanup:
    Tcl_Close(interp, chan);
    CleanupPNGImage(&png);
    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * StringWritePNG --
 *
 *	This function is called by the photo image type to write PNG format
 *	data to a Tcl object and return it in the result.
 *
 * Results:
 *	A standard TCL completion code. If TCL_ERROR is returned then an error
 *	message is left in the interp's result.
 *
 * Side effects:
 *	None
 *
 *----------------------------------------------------------------------
 */

static int
StringWritePNG(
    Tcl_Interp *interp,
    Tcl_Obj *fmtObj,
    Tk_PhotoImageBlock *blockPtr)
{
    Tcl_Obj *resultObj = Tcl_NewObj();
    PNGImage png;
    int result = TCL_ERROR;

    /*
     * Initalize PNGImage instance for encoding.
     */

    if (InitPNGImage(interp, &png, NULL, resultObj,
	    TCL_ZLIB_STREAM_DEFLATE) == TCL_ERROR) {
	goto cleanup;
    }

    /*
     * Write the raw PNG data into the prepared Tcl_Obj buffer. Set the result
     * back to the interpreter if successful.
     */

    result = EncodePNG(interp, blockPtr, &png);

    if (TCL_OK == result) {
	Tcl_SetObjResult(interp, png.objDataPtr);
    }

  cleanup:
    CleanupPNGImage(&png);
    return result;
}

/*
 * Local Variables:
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */