[GtkGLExt] [Repost] Re: GdkGLPixmap troubles

[Jose Commins <axora axora net>]

Hi, just to note a few caveats when dealing with GL contexts.

   First, before performing any context reference operations, the GL 
widget should be +realized+ to manipulate any references inside.  I have 
included some source code that I use in one of my apps to enlighten. 
with typecasts to make it easier to associate types:

   // Get OpenGL rendering context.
   gtk_widget_realize ((GtkWidget *) yourGLCapableWidget);
   (GdkGLContext *) theSharedGlContext = gtk_widget_get_gl_context 
((GtkWidget *) yourGLCapableWidget);
   // Initialise the other GL areas with the same shared context.
   (GtkWidget *) anotherGLWidget = GTK_WIDGET (gtk_builder_get_object 
(yourGTKBuilderXml, "GLwidget2"));
   // Add OpenGL-capability to the other widget, sharing the same context.
   gtk_widget_set_gl_capability ((GtkWidget *) anotherGLWidget, 
glConfig, (GdkGLContext *) theSharedGlContext, TRUE, GDK_GL_RGBA_TYPE);

... etc

   Note that 'gtk_widget_realize' is essential for the following 
functions to reference data within.

   Another caveat is that some drivers align texture data, depending on 
hardware - after the storage->framebuffer phase the alignment can vary 
if the hardware is not capable of non-powers-of-two textures.  You may 
find that the driver will texture-split any non-power-of-two 
rectangles.  The solution to this is to make sure that if the 
driver/hardware does not support non-power-of-two textures, to use the 
stride value in retrieving data back from the framebuffer.

Regards,
   Jose.