[GtkGLExt] Infuriating! gtk_widget_get_gl_context() and gtk_widget_get_gl_drawable() returns NULL!

[Rob Stoddard <rstoddard telanetix com>]

This is my fourth venture into GtkGL land...  All other times have been 
smooth sailing, but now I get trouble.


I am trying to make a mod to the gtk-vnc widget which will allow me to 
resize the widget.   I chose to use gtkglext and OpenGL to do the 
resizing.  However, there are two incidents of note here...  First, for 
some strange reason, the on_configure_event is being called before 
on_realize.   Is there any reason why this would happen?   Second, when 
I call gtk_widget_get_gl_context() and gtk_widget_get_gl_drawable(),  
they both return NULL.   I am initializing the GL library in the 
application. 

When I run gdk_gl_context_new I get the following assertion:
(lt-gvncviewer:2855): GdkGLExt-CRITICAL **: gdk_gl_context_new: 
assertion `GDK_IS_GL_DRAWABLE (gldrawable)' failed
even though the widget that I am using is inherited off of a GtkDrawingArea.


When I try to call gdk_gl_drawable_gl_begin I get the following assertion:
(lt-gvncviewer:1750): GdkGLExt-CRITICAL **: gdk_gl_drawable_gl_begin: 
assertion `GDK_IS_GL_DRAWABLE (gldrawable)' failed

The code I am using for my realize and configure event handlers is:


static void realize(VncDisplay *obj)
{
       printf("Realizing display.\n");
       GtkWidget *widget = GTK_WIDGET(obj);

printf("Beginning OGL init.\n");
 /* Try double-buffered visual */
 GdkGLConfig *glconfig = gdk_gl_config_new_by_mode (GDK_GL_MODE_RGB    |
                                                    GDK_GL_MODE_DEPTH  |
                                                    GDK_GL_MODE_DOUBLE);
 if (glconfig == NULL)
   {
     g_print ("*** Cannot find the double-buffered visual.\n");
     g_print ("*** Trying single-buffered visual.\n");

     /* Try single-buffered visual */
     glconfig = gdk_gl_config_new_by_mode (GDK_GL_MODE_RGB   |
                                           GDK_GL_MODE_DEPTH);
     if (glconfig == NULL)
       {
         g_print ("*** No appropriate OpenGL-capable visual found.\n");
         exit (1);
       }
   }
printf("beginning OGL+widget stuff with widget %p.\n", widget);
 obj->priv->glcontext = gdk_gl_context_new(widget, NULL, True, GL_RGBA);
 obj->priv->gldrawable = gtk_widget_get_gl_drawable (widget);

printf("OGL begin(%p, %p).\n", obj->priv->gldrawable, obj->priv->glcontext);
 /*** OpenGL BEGIN ***/
 if (!gdk_gl_drawable_gl_begin (obj->priv->gldrawable, 
obj->priv->glcontext))
   exit(-1);

printf("Starting in on the gl code.\n");

       glMatrixMode(GL_PROJECTION);
       glLoadIdentity();
       glOrtho(0, 1, 1, 0, 1, -1);
       glMatrixMode(GL_MODELVIEW);
       glLoadIdentity();
       glDisable(GL_DEPTH_TEST);
       glActiveTexture(GL_TEXTURE0);
       glEnable(GL_TEXTURE_RECTANGLE_ARB);
       glGenTextures(1, &obj->priv->frametex);
       obj->priv->displist = glGenLists(1);
       glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
printf("tex id is %d\n", obj->priv->frametex);

       glActiveTexture(GL_TEXTURE0);

glClearColor(0xff, 0xff, 0x00, 0x00);
OGLerror("glClearColor or earlier");
}



static void on_configure(VncDisplay *obj)
{
       printf("On_configure.\n");
       GtkWidget *widget = GTK_WIDGET(obj);
       int width = widget->allocation.width;
       int height = widget->allocation.height;

printf("on configure OGL begin(%p, %p).\n", obj->priv->gldrawable, 
obj->priv->glcontext);
       if(obj->priv->gldrawable == NULL || obj->priv->glcontext == NULL)
               return 0;

 if (!gdk_gl_drawable_gl_begin (obj->priv->gldrawable, 
obj->priv->glcontext))
   return 0;

printf("calling viewport with %dx%d\n", width, height);
       glViewport(0, 0, width, height);
       glBindTexture(GL_TEXTURE_RECTANGLE_ARB, obj->priv->frametex);
OGLerror("bind");
       glTexParameteri(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_WRAP_S, 
GL_CLAMP_TO_EDGE);
       glTexParameteri(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_WRAP_T, 
GL_CLAMP_TO_EDGE);
OGLerror("tex param");
       glTexImage2D(GL_TEXTURE_RECTANGLE_ARB, 0, GL_RGBA, width, 
height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
OGLerror("tex image 2d");

       glNewList(obj->priv->displist, GL_COMPILE);
       {
               glBegin(GL_QUADS);
               glTexCoord2f(0.0f, height);
               glVertex2f(0.0f, 1.0f);

               glTexCoord2f(width, height);
               glVertex2f(1.0f, 1.0f);

               glTexCoord2f(width, 0.0f);
               glVertex2f(1.0f, 0.0f);

               glTexCoord2f(0.0f, 0.0f);
               glVertex2f(0.0f, 0.0f);
               glEnd();
       }
       glEndList();
OGLerror("list creation and compilation");

       gdk_gl_drawable_gl_end (obj->priv->gldrawable);
}



The error is easy to recreate, all one must do is download the gtk-vnc 
package, add the gtk_gl_init function to the examples/gvncviewer.c 
file's main() function, add the code above to the src/vncdisplay.c file, 
stick the appropriate g_signal_connect calls.



Thank you for any assistance you may give in this matter.

R Stoddard