QOpenGLWidget: use (and prefer) InvalidateFramebuffer

Desktop GL does not have the GL_EXT_discard_framebuffer extension at
all. Instead, it may have GL_ARB_invalidate_subdata.

Furthermore, GLES >= 3.0 and GL >= 4.3 both support FBO invalidation
through glInvalidateFramebuffer.

Extend the semantics of OpenGLExtension::DiscardFramebuffer to mean that
*any* possibility above is supported, and wrap it in a helper function
that calls whatever support is present. (This is all private API
anyhow.) Technically speaking glInvalidateFramebuffer supports a
superset of what glDiscardFramebufferEXT supports, but we never use such
superset, and the two APIs are otherwise identical.

Then, make QOpenGLWidget call that wrapper.

Change-Id: I64e042daf51493d3834c3ba1b53ae6e224bbc4ed
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 1 insertions, 9 deletions

diff --git a/src/gui/opengl/qopenglextensions_p.h b/src/gui/opengl/qopenglextensions_p.h
index 58231545c6..a6c4a68c6c 100644
--- a/src/gui/opengl/qopenglextensions_p.h
+++ b/src/gui/opengl/qopenglextensions_p.h
@@ -70,9 +70,9 @@ public:
 
     GLvoid *glMapBuffer(GLenum target, GLenum access);
     void glGetBufferSubData(GLenum target, qopengl_GLintptr offset, qopengl_GLsizeiptr size, GLvoid *data);
-    void glDiscardFramebufferEXT (GLenum target, GLsizei numAttachments, const GLenum *attachments);
 
     void flushShared();
+    void discardFramebuffer(GLenum target, GLsizei numAttachments, const GLenum *attachments);
 
     QOpenGLExtensionsPrivate *d() const;
 
@@ -117,14 +117,6 @@ inline void QOpenGLExtensions::glGetBufferSubData(GLenum target, qopengl_GLintpt
     Q_OPENGL_FUNCTIONS_DEBUG
 }
 
-
-inline void QOpenGLExtensions::glDiscardFramebufferEXT (GLenum target, GLsizei numAttachments, const GLenum *attachments)
-{
-    Q_D(QOpenGLExtensions);
-    Q_ASSERT(QOpenGLExtensions::isInitialized(d));
-    d->DiscardFramebuffer(target,numAttachments, attachments);
-    Q_OPENGL_FUNCTIONS_DEBUG
-}
 QT_END_NAMESPACE
 
 #endif // QOPENGL_EXTENSIONS_P_H