OpenGL uses a depth range between -1 and 1, which is then normalized.
Metal & Vulkan uses a depth range between 0 and 1, which is already normalized.
The final plan would be to default to a depth range between 0 and 1, but
for now the depth ranges are retargetted so they won't be clipped away.
This solves the next issues for users:
- Navigate control will be rendered correctly
- Ortographic view clipping artifacts
- EEVEE light evaluation
Retargetting happens at the end of the vertex stage or when a geometry
stage is present at the end of the geometry stage. Derivatives using
depth would have a different value compared to OpenGL, but would match
Metal backend. OpenGL performs clipping and generates derivatives based
on the original depth value.
`gl_FragCoord` and clipping would have some precision differences as clipping
and normalizing are done in a different order but would match Metal.
Geometry shaders should use `gpu_EmitVertex` to ensure that the retargetting
is done per vertex.
Pull Request: https://projects.blender.org/blender/blender/pulls/114669
0c9433bf44