This solves the regression with NVIDIA drivers resulting in a black screen.
Apparently NVIDIA does not support glXCopySubBuffer and the copying of pixels
fails with a shader bound.
So unbinding the shader before copying the pixels and rebinding the shader
afterwards resolves the issue.
This allows to remove the temporary hack to make NVIDIA work, again.
Apparently glXQueryDrawable does not work in NVIDIA blob for binding
a texture from an icon. This fixes an abort, but the root cause should
be found and fixed properly.
Our primary target is Texture From Pixmap and it is supported
by all important drivers nowadays. If a driver is not able to
support TFP using OpenGL at all is probably no good idea and
XRender is more suited.
A color can be specified to render the geometry of the VBO.
For legacy painting glColor is used, for shader a uniform is set.
In order to allow rendering without texcoords, it is possible to pass
a null pointer as texcoords.
Shader added to scene which just renders a colored geometry without texturing.
