it made it actually more confusing to have two version of the uv
(normalized and not). Also the unnormalized version was computed from
frameUniforms which is not great in the case of post-processing
(it just happened to work).
If you tried removing `culling: none` from any post-process materials,
everything would be fine in GL but Vulkan would be black because
our full-screen triangle was back-facing.
Continue reading only if you thrive in absurd situations.
- Metal and OpenGL define clip space as Y-up whereas Vulkan is Y-down.
- Metal and Vulkan define tex coords as Y-down whereas OpenGL is Y-up.
