Fixed crash in GL 2 paint engine on Intel Atom.

The GPU in question supports GL 2 but not framebuffer objects. Since we
anyway have a font rendering path that doesn't use FBOs we might as well
not require framebuffer objects in order to use the GL 2 engine.

Task-number: QTBUG-22483
Change-Id: I2a80343fedda276e73e603ffe54edff58801af5b
Reviewed-by: Kim M. Kalland <kim.kalland@nokia.com>

4 files changed, 16 insertions, 12 deletions

diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
index 323b0c0..89a7264 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
@@ -1455,7 +1455,8 @@ void QGL2PaintEngineEx::drawStaticTextItem(QStaticTextItem *textItem)
                                                 ? QFontEngineGlyphCache::Type(textItem->fontEngine()->glyphFormat)
                                                 : d->glyphCacheType;
         if (glyphType == QFontEngineGlyphCache::Raster_RGBMask) {
-            if (d->device->alphaRequested() || s->matrix.type() > QTransform::TxTranslate
+            if (!QGLFramebufferObject::hasOpenGLFramebufferObjects()
+                || d->device->alphaRequested() || s->matrix.type() > QTransform::TxTranslate
                 || (s->composition_mode != QPainter::CompositionMode_Source
                 && s->composition_mode != QPainter::CompositionMode_SourceOver))
             {
@@ -1518,7 +1519,8 @@ void QGL2PaintEngineEx::drawTextItem(const QPointF &p, const QTextItem &textItem
 
 
     if (glyphType == QFontEngineGlyphCache::Raster_RGBMask) {
-        if (d->device->alphaRequested() || txtype > QTransform::TxTranslate
+        if (!QGLFramebufferObject::hasOpenGLFramebufferObjects()
+            || d->device->alphaRequested() || txtype > QTransform::TxTranslate
             || (state()->composition_mode != QPainter::CompositionMode_Source
             && state()->composition_mode != QPainter::CompositionMode_SourceOver))
         {
@@ -2139,7 +2141,9 @@ bool QGL2PaintEngineEx::begin(QPaintDevice *pdev)
 
 #if !defined(QT_OPENGL_ES_2)
     bool success = qt_resolve_version_2_0_functions(d->ctx)
-                   && qt_resolve_buffer_extensions(d->ctx);
+                   && qt_resolve_buffer_extensions(d->ctx)
+                   && (!QGLFramebufferObject::hasOpenGLFramebufferObjects()
+                       || qt_resolve_framebufferobject_extensions(d->ctx));
     Q_ASSERT(success);
     Q_UNUSED(success);
 #endif
diff --git a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
index 571f482..ac11641 100644
--- a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
+++ b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
@@ -111,7 +111,7 @@ void QGLTextureGlyphCache::createTextureData(int width, int height)
     // create in QImageTextureGlyphCache baseclass is meant to be called
     // only to create the initial image and does not preserve the content,
     // so we don't call when this function is called from resize.
-    if (ctx->d_ptr->workaround_brokenFBOReadBack && image().isNull())
+    if ((!QGLFramebufferObject::hasOpenGLFramebufferObjects() || ctx->d_ptr->workaround_brokenFBOReadBack) && image().isNull())
         QImageTextureGlyphCache::createTextureData(width, height);
 
     // Make the lower glyph texture size 16 x 16.
@@ -166,7 +166,7 @@ void QGLTextureGlyphCache::resizeTextureData(int width, int height)
     GLuint oldTexture = glyphTexture->m_texture;
     createTextureData(width, height);
 
-    if (ctx->d_ptr->workaround_brokenFBOReadBack) {
+    if (!QGLFramebufferObject::hasOpenGLFramebufferObjects() || ctx->d_ptr->workaround_brokenFBOReadBack) {
         QImageTextureGlyphCache::resizeTextureData(width, height);
         Q_ASSERT(image().depth() == 8);
         glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, width, oldHeight, GL_ALPHA, GL_UNSIGNED_BYTE, image().constBits());
@@ -286,7 +286,7 @@ void QGLTextureGlyphCache::fillTexture(const Coord &c, glyph_t glyph, QFixed sub
     }
 
     QGLGlyphTexture *glyphTexture = m_textureResource.value(ctx);
-    if (ctx->d_ptr->workaround_brokenFBOReadBack) {
+    if (!QGLFramebufferObject::hasOpenGLFramebufferObjects() || ctx->d_ptr->workaround_brokenFBOReadBack) {
         QImageTextureGlyphCache::fillTexture(c, glyph, subPixelPosition);
 
         glBindTexture(GL_TEXTURE_2D, glyphTexture->m_texture);
diff --git a/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h b/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
index bb34efb..c5a8857 100644
--- a/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
+++ b/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
@@ -56,6 +56,7 @@
 #include <private/qtextureglyphcache_p.h>
 #include <private/qgl_p.h>
 #include <qglshaderprogram.h>
+#include <qglframebufferobject.h>
 
 // #define QT_GL_TEXTURE_GLYPH_CACHE_DEBUG
 
@@ -66,10 +67,11 @@ class QGL2PaintEngineExPrivate;
 struct QGLGlyphTexture
 {
     QGLGlyphTexture(const QGLContext *ctx)
-        : m_width(0)
+        : m_fbo(0)
+        , m_width(0)
         , m_height(0)
     {
-        if (ctx && !ctx->d_ptr->workaround_brokenFBOReadBack)
+        if (ctx && QGLFramebufferObject::hasOpenGLFramebufferObjects() && !ctx->d_ptr->workaround_brokenFBOReadBack)
             glGenFramebuffers(1, &m_fbo);
 
 #ifdef QT_GL_TEXTURE_GLYPH_CACHE_DEBUG
@@ -85,7 +87,7 @@ struct QGLGlyphTexture
         // At this point, the context group is made current, so it's safe to
         // release resources without a makeCurrent() call
         if (ctx) {
-            if (!ctx->d_ptr->workaround_brokenFBOReadBack)
+            if (m_fbo)
                 glDeleteFramebuffers(1, &m_fbo);
             if (m_width || m_height)
                 glDeleteTextures(1, &m_texture);
diff --git a/src/opengl/qglextensions.cpp b/src/opengl/qglextensions.cpp
index c955728..60f7055 100644
--- a/src/opengl/qglextensions.cpp
+++ b/src/opengl/qglextensions.cpp
@@ -40,6 +40,7 @@
 ****************************************************************************/
 
 #include "qgl_p.h"
+#include <qglframebufferobject.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -418,9 +419,6 @@ bool qt_resolve_version_2_0_functions(QGLContext *ctx)
     if (!qt_resolve_version_1_3_functions(ctx))
         gl2supported = false;
 
-    if (!qt_resolve_framebufferobject_extensions(ctx))
-        gl2supported = false;
-
     if (glStencilOpSeparate)
         return gl2supported;