Rework how Qt handles GL extensions.

Qt used to store the GL extensions a particular implementation supported
in a global cache, which was initialized once and never updated.
This could cause problems because different types of context might
support different kinds of extensions (e.g. the difference between
sw and hw contexts). With this patch, the GL extensions are cached
and updated within each QGLContext. It also makes the extension
initialization lazy, which saves application initialization costs for
embedded platforms.
The patch introduces a internal cross platform QGLTemporaryContext
class that is used to create a light-weight GL context without going
via QGLWidget and friends (QWS and WinCE still have QGLWidget fallbacks
for now).

Reviewed-by: Kim
Reviewed-by: Samuel

1 files changed, 62 insertions, 23 deletions

diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index a262ded..09ecfd1 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -124,9 +124,6 @@ public:
 };
 Q_GLOBAL_STATIC(QGLDefaultOverlayFormat, defaultOverlayFormatInstance)
 
-QGLExtensions::Extensions QGLExtensions::glExtensions = 0;
-bool QGLExtensions::nvidiaFboNeedsFinish = false;
-
 Q_GLOBAL_STATIC(QGLSignalProxy, theSignalProxy)
 QGLSignalProxy *QGLSignalProxy::instance()
 {
@@ -154,11 +151,9 @@ public:
         // falling back to the GL 1 engine..
         static bool mac_x1600_check_done = false;
         if (!mac_x1600_check_done) {
-            QGLWidget *tmp = 0;
-            if (!QGLContext::currentContext()) {
-                tmp = new QGLWidget();
-                tmp->makeCurrent();
-            }
+            QGLTemporaryContext *tmp = 0;
+            if (!QGLContext::currentContext())
+                tmp = new QGLTemporaryContext();
             if (strstr((char *) glGetString(GL_RENDERER), "X1600"))
                 engineType = QPaintEngine::OpenGL;
             if (tmp)
@@ -178,7 +173,7 @@ public:
             // from an old GL 1.1 server to a GL 2.x client. In that case we can't
             // use GL 2.0.
             if ((QGLFormat::openGLVersionFlags() & QGLFormat::OpenGL_Version_2_0)
-                && (QGLExtensions::glExtensions & QGLExtensions::FragmentShader)
+                && (QGLExtensions::glExtensions() & QGLExtensions::FragmentShader)
                 && qgetenv("QT_GL_USE_OPENGL1ENGINE").isEmpty())
                 engineType = QPaintEngine::OpenGL2;
             else
@@ -1250,7 +1245,7 @@ QGLFormat::OpenGLVersionFlags QGLFormat::openGLVersionFlags()
     static bool cachedDefault = false;
     static OpenGLVersionFlags defaultVersionFlags = OpenGL_Version_None;
     QGLContext *currentCtx = const_cast<QGLContext *>(QGLContext::currentContext());
-    QGLWidget *dummy = 0;
+    QGLTemporaryContext *tmpContext = 0;
 
     if (currentCtx && currentCtx->d_func()->version_flags_cached)
         return currentCtx->d_func()->version_flags;
@@ -1261,8 +1256,7 @@ QGLFormat::OpenGLVersionFlags QGLFormat::openGLVersionFlags()
         } else {
             if (!hasOpenGL())
                 return defaultVersionFlags;
-            dummy = new QGLWidget;
-            dummy->makeCurrent(); // glGetString() needs a current context
+            tmpContext = new QGLTemporaryContext;
             cachedDefault = true;
         }
     }
@@ -1273,9 +1267,9 @@ QGLFormat::OpenGLVersionFlags QGLFormat::openGLVersionFlags()
         currentCtx->d_func()->version_flags_cached = true;
         currentCtx->d_func()->version_flags = versionFlags;
     }
-    if (dummy) {
+    if (tmpContext) {
         defaultVersionFlags = versionFlags;
-        delete dummy;
+        delete tmpContext;
     }
 
     return versionFlags;
@@ -1493,6 +1487,8 @@ void QGLContextPrivate::init(QPaintDevice *dev, const QGLFormat &format)
     max_texture_size = -1;
     version_flags_cached = false;
     version_flags = QGLFormat::OpenGL_Version_None;
+    extension_flags_cached = false;
+    extension_flags = 0;
     current_fbo = 0;
     default_fbo = 0;
     active_engine = 0;
@@ -2147,7 +2143,7 @@ QGLTexture* QGLContextPrivate::bindTexture(const QImage &image, GLenum target, G
     int tx_h = qt_next_power_of_two(image.height());
 
     QImage img = image;
-    if (!(QGLExtensions::glExtensions & QGLExtensions::NPOTTextures)
+    if (!(QGLExtensions::glExtensions() & QGLExtensions::NPOTTextures)
         && !(QGLFormat::openGLVersionFlags() & QGLFormat::OpenGL_ES_Version_2_0)
         && (target == GL_TEXTURE_2D && (tx_w != image.width() || tx_h != image.height())))
     {
@@ -2169,7 +2165,7 @@ QGLTexture* QGLContextPrivate::bindTexture(const QImage &image, GLenum target, G
     bool genMipmap = false;
 #endif
     if (glFormat.directRendering()
-        && (QGLExtensions::glExtensions & QGLExtensions::GenerateMipmap)
+        && (QGLExtensions::glExtensions() & QGLExtensions::GenerateMipmap)
         && target == GL_TEXTURE_2D
         && (options & QGLContext::MipmapBindOption))
     {
@@ -2197,7 +2193,7 @@ QGLTexture* QGLContextPrivate::bindTexture(const QImage &image, GLenum target, G
     bool premul = options & QGLContext::PremultipliedAlphaBindOption;
     GLenum externalFormat;
     GLuint pixel_type;
-    if (QGLExtensions::glExtensions & QGLExtensions::BGRATextureFormat) {
+    if (QGLExtensions::glExtensions() & QGLExtensions::BGRATextureFormat) {
         externalFormat = GL_BGRA;
         pixel_type = GL_UNSIGNED_INT_8_8_8_8_REV;
     } else {
@@ -4868,9 +4864,13 @@ QGLWidget::QGLWidget(QGLContext *context, QWidget *parent,
 
 #endif // QT3_SUPPORT
 
-void QGLExtensions::init_extensions()
+/*
+    Returns the GL extensions for the current context.
+*/
+QGLExtensions::Extensions QGLExtensions::currentContextExtensions()
 {
     QGLExtensionMatcher extensions(reinterpret_cast<const char *>(glGetString(GL_EXTENSIONS)));
+    Extensions glExtensions;
 
     if (extensions.match("GL_ARB_texture_rectangle"))
         glExtensions |= TextureRectangle;
@@ -4931,6 +4931,46 @@ void QGLExtensions::init_extensions()
 
     if (extensions.match("GL_EXT_bgra"))
         glExtensions |= BGRATextureFormat;
+
+    return glExtensions;
+}
+
+/*
+    Returns the GL extensions for the current QGLContext. If there is no
+    current QGLContext, a default context will be created and the extensions
+    for that context will be returned instead.
+*/
+QGLExtensions::Extensions QGLExtensions::glExtensions()
+{
+    QGLTemporaryContext *tmpContext = 0;
+    static bool cachedDefault = false;
+    static Extensions defaultExtensions = 0;
+    QGLContext *currentCtx = const_cast<QGLContext *>(QGLContext::currentContext());
+
+    if (currentCtx && currentCtx->d_func()->extension_flags_cached)
+        return currentCtx->d_func()->extension_flags;
+
+    if (!currentCtx) {
+        if (cachedDefault) {
+            return defaultExtensions;
+        } else {
+            tmpContext = new QGLTemporaryContext;
+            cachedDefault = true;
+        }
+    }
+
+    Extensions extensionFlags = currentContextExtensions();
+    if (currentCtx) {
+        currentCtx->d_func()->extension_flags_cached = true;
+        currentCtx->d_func()->extension_flags = extensionFlags;
+    } else {
+        defaultExtensions = extensionFlags;
+    }
+
+    if (tmpContext)
+        delete tmpContext;
+
+    return extensionFlags;
 }
 
 /*
@@ -4942,7 +4982,6 @@ void QGLWidgetPrivate::initContext(QGLContext *context, const QGLWidget* shareWi
 
     glDevice.setWidget(q);
 
-    QGLExtensions::init();
     glcx = 0;
     autoSwap = true;
 
@@ -5191,7 +5230,7 @@ QSize QGLTexture::bindCompressedTexture
     }
 #if !defined(QT_OPENGL_ES)
     if (!glCompressedTexImage2D) {
-        if (!(QGLExtensions::glExtensions & QGLExtensions::TextureCompression)) {
+        if (!(QGLExtensions::glExtensions() & QGLExtensions::TextureCompression)) {
             qWarning("QGLContext::bindTexture(): The GL implementation does "
                      "not support texture compression extensions.");
             return QSize();
@@ -5230,7 +5269,7 @@ QSize QGLTexture::bindCompressedTextureDDS(const char *buf, int len)
         return QSize();
 
     // Bail out if the necessary extension is not present.
-    if (!(QGLExtensions::glExtensions & QGLExtensions::DDSTextureCompression)) {
+    if (!(QGLExtensions::glExtensions() & QGLExtensions::DDSTextureCompression)) {
         qWarning("QGLContext::bindTexture(): DDS texture compression is not supported.");
         return QSize();
     }
@@ -5340,13 +5379,13 @@ QSize QGLTexture::bindCompressedTexturePVR(const char *buf, int len)
 
     // Bail out if the necessary extension is not present.
     if (textureFormat == GL_ETC1_RGB8_OES) {
-        if (!(QGLExtensions::glExtensions &
+        if (!(QGLExtensions::glExtensions() &
                     QGLExtensions::ETC1TextureCompression)) {
             qWarning("QGLContext::bindTexture(): ETC1 texture compression is not supported.");
             return QSize();
         }
     } else {
-        if (!(QGLExtensions::glExtensions &
+        if (!(QGLExtensions::glExtensions() &
                     QGLExtensions::PVRTCTextureCompression)) {
             qWarning("QGLContext::bindTexture(): PVRTC texture compression is not supported.");
             return QSize();