In the DrawManager a dummy texture was attached to the a, au, c, ac
binding points. In the shader those binding points are actual texture
buffers.
The reason for the dummy texture was to work around some OpenGL driver
bugs. In Vulkan (and expected also in Metal) it is not allowed to attach
a texture as a texel buffer and would require copying buffers into a
texel buffer during binding.
This patch will remove the binding of the textures and use the vbos in
stead. Also it fixes an issue where a platform does support compute
shaders, but don't support transform feedback. This is currently the
case for the Vulkan backend.
Jeroen Bakker