Add a Viewport property to use full floating-point precision

[Calinou]

master version of #51708.

This is only available on the Vulkan Clustered backend.

This can be useful for advanced shaders, but it should generally not be enabled otherwise as full precision has a performance cost. For general-purpose rendering, the built-in debanding filter should be used to reduce banding instead.

This closes godotengine/godot-proposals#2935.

Testing project: test_32bpc_master.zip

Preview

While I don't have a suitable shader for testing the difference, I can note that there is a subtle visual difference in a test scene I made (verified by dssim).

No MSAA

16 bpc (default)

32 bpc

Difference

8× MSAA

16 bpc (default)

32 bpc

Difference

[reduz]

This is not going to work as-is, and its likely triggering lots of validation layer errors. You need to fix all the compute shaders and add variants that work with 32bpp, as the format needs to be explicited in image load/store. I think its not worth the effort.

[FishOfTheNorthStar]

Just wanted to chime in and explain why this option would help me. I'm trying to generate Terrain3D control maps inside a canvasitem shader, because that would be quite a lot faster than bit banging it per pixel in an Image. Except Terrain3D is using Rf (32 bit), converted in their shader to 32 bit uint. So when I generate the appropriate uint 32 in my control-map-maker, internally Godot is mangling it down to 16bpc, which of course doesn't work out.

For now I'm doing it the kinda slow way, CPU side, but it's a shame cause it's easily 20 times slower. Is there perhaps a way I could use two 16 bpc output channels in my shader, like Red and Green, then cpu side, merge them together into a true 32bpc reconstructed single channel image? Looking into this now but if anyone has any work arounds to this use case that'd be very helpful.