Fix GL_DEPTH_TEST for GL code examples after adding image shader
Fix build warnings in sdc/bilinearScheme and sdc/catmarkScheme
Fixes the bug of glShareTopology. This example mutates patchDescriptor in drawcontext, so it needs a write access.
Adding another GetPatchArray() returning non-const reference. We should think about better API for this.
Fixes GL error caused by incomplete framebuffer on hud initialization.