The most important change here is that we no longer apply the
backend (e.g. Metal/Vulkan) UV transformation before calling the
user's vertex shader. This is an API change for post-process materials
(but they're not public).
Now the user is responsible for using uvToRenderTargetUV() in their
shaders (either in the fragment or vertex as appropriate).
This makes it easier to handle offsets/transforms with all APIs.
Conceptually, the only thing that is needed is to call
uvToRenderTargetUV() just before making a texture call.
This fixes a couple of issues:
- some image shifting in metal/vk
- flare in metal/vk was upside down
We also simplify the DoF code quite a bit now that we can rely on the
rendertargets begin multiple of 16.
We also "fix" SSAO that was working by accident on metal/vk. The UV
correction was applied 3 times 2 of which were canceling each other.
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