Improve pi4 vulkan support

[dpjudas]

Removed depthClamp requirement (note: portals will not render correctly on such devices).
Added format fallback support for VK_FORMAT_A2R10G10B10_UNORM_PACK32 since the pi4 doesn't support it.

[alexey-lysiuk]

I tried simple portal test maps with depth clamp disabled, and they seem to work fine.
The only thing I noticed is visual glitch when moving through interactive portal.
It's an acceptable shortcoming I think.

[dpjudas]

It is. The shortcoming is actually exactly the same as was reported for softpoly recently. It too had no support for depth clamp. :)

[coelckers]

Is lack of depth clamp a Pi4 issue or something more general with ARM? It's a bit strange for this recent hardware not having support for something being taken for granted for 10+ years.

[madame-rachelle]

This really should not have anything to do with ARM. The VideoCore processor (which is the Pi4's GPU) is embedded in the CPU like an integrated Intel GPU chip, but that's the extent of it. ARM processors, if in a system that supports them, can use full fledged NVidia/ATI GPU's that would not be affected by such a bug.

[madame-rachelle]

Also I think I should point out that this may also simply be a driver issue, as well.

[Cacodemon345]

Has the lack of depth clamp been reported to the Mesa3D developers?

[madame-rachelle]

No. If anyone wants to do that be my guest. This issue simply is not important enough to me for me to bother.

[dpjudas]

The depth clamp thing isn't an ARM issue as the M1 runs it just fine without. It is either the pi4 driver not implementing depth clamp, or the GPU implementation not supporting it.

Note that this is technically not a bug. A vulkan compliant driver is allowed to not support depth clamp.