path: root/doc/GetBitmap.3

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'\" Copyright (c) 1994-1998 Sun Microsystems, Inc.
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'\" RCS: @(#) $Id: GetBitmap.3,v 1.17 2009/02/27 23:23:36 nijtmans Exp $
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.so man.macros
.TH Tk_AllocBitmapFromObj 3 8.1 Tk "Tk Library Procedures"
.BS
.SH NAME
Tk_AllocBitmapFromObj, Tk_GetBitmap, Tk_GetBitmapFromObj, Tk_DefineBitmap, Tk_NameOfBitmap, Tk_SizeOfBitmap, Tk_FreeBitmapFromObj, Tk_FreeBitmap \- maintain database of single-plane pixmaps
.SH SYNOPSIS
.nf
\fB#include <tk.h>\fR
.sp
Pixmap
\fBTk_AllocBitmapFromObj(\fIinterp, tkwin, objPtr\fB)\fR
.sp
Pixmap
\fBTk_GetBitmap(\fIinterp, tkwin, info\fB)\fR
.sp
Pixmap
\fBTk_GetBitmapFromObj(\fItkwin, objPtr\fB)\fR
.sp
int
\fBTk_DefineBitmap(\fIinterp, name, source, width, height\fB)\fR
.sp
const char *
\fBTk_NameOfBitmap(\fIdisplay, bitmap\fB)\fR
.sp
\fBTk_SizeOfBitmap(\fIdisplay, bitmap, widthPtr, heightPtr\fB)\fR
.sp
\fBTk_FreeBitmapFromObj(\fItkwin, objPtr\fB)\fR
.sp
\fBTk_FreeBitmap(\fIdisplay, bitmap\fB)\fR
.SH ARGUMENTS
.AS "unsigned long" *pixelPtr
.AP Tcl_Interp *interp in
Interpreter to use for error reporting; if NULL then no error message
is left after errors.
.AP Tk_Window tkwin in
Token for window in which the bitmap will be used.
.AP Tcl_Obj *objPtr in/out
String value describes desired bitmap; internal rep will be
modified to cache pointer to corresponding Pixmap.
.AP "const char" *info in
Same as \fIobjPtr\fR except description of bitmap is passed as a string and
resulting Pixmap is not cached.
.AP "const char" *name in
Name for new bitmap to be defined.
.AP "const void" *source in
Data for bitmap, in standard bitmap format.
Must be stored in static memory whose value will never change.
.AP "int" width in
Width of bitmap.
.AP "int" height in
Height of bitmap.
.AP "int" *widthPtr out
Pointer to word to fill in with \fIbitmap\fR's width.
.AP "int" *heightPtr out
Pointer to word to fill in with \fIbitmap\fR's height.
.AP Display *display in
Display for which \fIbitmap\fR was allocated.
.AP Pixmap bitmap in
Identifier for a bitmap allocated by \fBTk_AllocBitmapFromObj\fR or
\fBTk_GetBitmap\fR.
.BE
.SH DESCRIPTION
.PP
These procedures manage a collection of bitmaps (one-plane pixmaps)
being used by an application.  The procedures allow bitmaps to be
re-used efficiently, thereby avoiding server overhead, and also
allow bitmaps to be named with character strings.
.PP
\fBTk_AllocBitmapFromObj\fR returns a Pixmap identifier for a bitmap
that matches the description in \fIobjPtr\fR and is suitable for use
in \fItkwin\fR.  It re-uses an existing bitmap, if possible, and
creates a new one otherwise.  \fIObjPtr\fR's value must have one
of the following forms:
.TP 20
\fB@\fIfileName\fR
\fIFileName\fR must be the name of a file containing a bitmap
description in the standard X11 format.
.TP 20
\fIname\fR
\fIName\fR must be the name of a bitmap defined previously with
a call to \fBTk_DefineBitmap\fR.  The following names are pre-defined
by Tk:
.RS
.TP 12
\fBerror\fR
The international
.QW don't
symbol:  a circle with a diagonal line across it.
.TP 12
\fBgray75\fR
75% gray: a checkerboard pattern where three out of four bits are on.
.TP 12
\fBgray50\fR
50% gray: a checkerboard pattern where every other bit is on.
.TP 12
\fBgray25\fR
25% gray: a checkerboard pattern where one out of every four bits is on.
.TP 12
\fBgray12\fR
12.5% gray: a pattern where one-eighth of the bits are on, consisting of
every fourth pixel in every other row.
.TP 12
\fBhourglass\fR
An hourglass symbol.
.TP 12
\fBinfo\fR
A large letter
.QW i .
.TP 12
\fBquesthead\fR
The silhouette of a human head, with a question mark in it.
.TP 12
\fBquestion\fR
A large question-mark.
.TP 12
\fBwarning\fR
A large exclamation point.
.PP
In addition, the following pre-defined names are available only on the
\fBMacintosh\fR platform:
.TP 12
\fBdocument\fR
A generic document.
.TP 12
\fBstationery\fR
Document stationery.
.TP 12
\fBedition\fR
The \fIedition\fR symbol.
.TP 12
\fBapplication\fR
Generic application icon.
.TP 12
\fBaccessory\fR
A desk accessory.
.TP 12
\fBfolder\fR
Generic folder icon.
.TP 12
\fBpfolder\fR
A locked folder.
.TP 12
\fBtrash\fR
A trash can.
.TP 12
\fBfloppy\fR
A floppy disk.
.TP 12
\fBramdisk\fR
A floppy disk with chip.
.TP 12
\fBcdrom\fR
A cd disk icon.
.TP 12
\fBpreferences\fR
A folder with prefs symbol.
.TP 12
\fBquerydoc\fR
A database document icon.
.TP 12
\fBstop\fR
A stop sign.
.TP 12
\fBnote\fR
A face with balloon words.
.TP 12
\fBcaution\fR
A triangle with an exclamation point.
.RE
.LP
Under normal conditions, \fBTk_AllocBitmapFromObj\fR
returns an identifier for the requested bitmap.  If an error
occurs in creating the bitmap, such as when \fIobjPtr\fR refers
to a non-existent file, then \fBNone\fR is returned and an error
message is left in \fIinterp\fR's result if \fIinterp\fR is not
NULL. \fBTk_AllocBitmapFromObj\fR caches information about the return
value in \fIobjPtr\fR, which speeds up future calls to procedures
such as \fBTk_AllocBitmapFromObj\fR and \fBTk_GetBitmapFromObj\fR.
.PP
\fBTk_GetBitmap\fR is identical to \fBTk_AllocBitmapFromObj\fR except
that the description of the bitmap is specified with a string instead
of an object.  This prevents \fBTk_GetBitmap\fR from caching the
return value, so \fBTk_GetBitmap\fR is less efficient than
\fBTk_AllocBitmapFromObj\fR.
.PP
\fBTk_GetBitmapFromObj\fR returns the token for an existing bitmap, given
the window and description used to create the bitmap.
\fBTk_GetBitmapFromObj\fR does not actually create the bitmap; the bitmap
must already have been created with a previous call to
\fBTk_AllocBitmapFromObj\fR or \fBTk_GetBitmap\fR.  The return
value is cached in \fIobjPtr\fR, which speeds up
future calls to \fBTk_GetBitmapFromObj\fR with the same \fIobjPtr\fR
and \fItkwin\fR.
.PP
\fBTk_DefineBitmap\fR associates a name with
in-memory bitmap data so that the name can be used in later
calls to \fBTk_AllocBitmapFromObj\fR or \fBTk_GetBitmap\fR.  The \fInameId\fR
argument gives a name for the bitmap;  it must not previously
have been used in a call to \fBTk_DefineBitmap\fR.
The arguments \fIsource\fR, \fIwidth\fR, and \fIheight\fR
describe the bitmap.
\fBTk_DefineBitmap\fR normally returns \fBTCL_OK\fR; if an error occurs
(e.g. a bitmap named \fInameId\fR has already been defined) then
\fBTCL_ERROR\fR is returned and an error message is left in
\fIinterp->result\fR.
Note:  \fBTk_DefineBitmap\fR expects the memory pointed to by
\fIsource\fR to be static:  \fBTk_DefineBitmap\fR does not make
a private copy of this memory, but uses the bytes pointed to
by \fIsource\fR later in calls to \fBTk_AllocBitmapFromObj\fR or
\fBTk_GetBitmap\fR.
.PP
Typically \fBTk_DefineBitmap\fR is used by \fB#include\fR-ing a
bitmap file directly into a C program and then referencing
the variables defined by the file.
For example, suppose there exists a file \fBstip.bitmap\fR,
which was created by the \fBbitmap\fR program and contains
a stipple pattern.
The following code uses \fBTk_DefineBitmap\fR to define a
new bitmap named \fBfoo\fR:
.CS
Pixmap bitmap;
#include "stip.bitmap"
Tk_DefineBitmap(interp, "foo", stip_bits,
    stip_width, stip_height);
\&...
bitmap = Tk_GetBitmap(interp, tkwin, "foo");
.CE
This code causes the bitmap file to be read
at compile-time and incorporates the bitmap information into
the program's executable image.  The same bitmap file could be
read at run-time using \fBTk_GetBitmap\fR:
.CS
Pixmap bitmap;
bitmap = Tk_GetBitmap(interp, tkwin, "@stip.bitmap");
.CE
The second form is a bit more flexible (the file could be modified
after the program has been compiled, or a different string could be
provided to read a different file), but it is a little slower and
requires the bitmap file to exist separately from the program.
.PP
Tk maintains a database of all the bitmaps that are currently in use.
Whenever possible, it will return an existing bitmap rather
than creating a new one.
When a bitmap is no longer used, Tk will release it automatically.
This approach can substantially reduce server overhead, so
\fBTk_AllocBitmapFromObj\fR and \fBTk_GetBitmap\fR should generally
be used in preference to Xlib procedures like \fBXReadBitmapFile\fR.
.PP
The bitmaps returned by \fBTk_AllocBitmapFromObj\fR and \fBTk_GetBitmap\fR
are shared, so callers should never modify them.
If a bitmap must be modified dynamically, then it should be
created by calling Xlib procedures such as \fBXReadBitmapFile\fR
or \fBXCreatePixmap\fR directly.
.PP
The procedure \fBTk_NameOfBitmap\fR is roughly the inverse of
\fBTk_GetBitmap\fR.
Given an X Pixmap argument, it returns the textual description that was
passed to \fBTk_GetBitmap\fR when the bitmap was created.
\fIBitmap\fR must have been the return value from a previous
call to \fBTk_AllocBitmapFromObj\fR or \fBTk_GetBitmap\fR.
.PP
\fBTk_SizeOfBitmap\fR returns the dimensions of its \fIbitmap\fR
argument in the words pointed to by the \fIwidthPtr\fR and
\fIheightPtr\fR arguments.  As with \fBTk_NameOfBitmap\fR,
\fIbitmap\fR must have been created by \fBTk_AllocBitmapFromObj\fR or
\fBTk_GetBitmap\fR.
.PP
When a bitmap is no longer needed, \fBTk_FreeBitmapFromObj\fR or
\fBTk_FreeBitmap\fR should be called to release it.
For \fBTk_FreeBitmapFromObj\fR the bitmap to release is specified
with the same information used to create it; for
\fBTk_FreeBitmap\fR the bitmap to release is specified
with its Pixmap token.
There should be exactly one call to \fBTk_FreeBitmapFromObj\fR
or \fBTk_FreeBitmap\fR for each call to \fBTk_AllocBitmapFromObj\fR or
\fBTk_GetBitmap\fR.
.SH BUGS
.PP
In determining whether an existing bitmap can be used to satisfy
a new request, \fBTk_AllocBitmapFromObj\fR and \fBTk_GetBitmap\fR
consider only the immediate value of the string description.  For
example, when a file name is passed to \fBTk_GetBitmap\fR,
\fBTk_GetBitmap\fR will assume it is safe to re-use an existing
bitmap created from the same file name:  it will not check to
see whether the file itself has changed, or whether the current
directory has changed, thereby causing the name to refer to
a different file.
.SH KEYWORDS
bitmap, pixmap