Depth reading features on devices without framebuffer fetch are relying on undefined behaviour.

For devices without framebuffer fetch we are relying on undefined behaviour for depth reading with decals, mod shadows and depth reading materials. (ES2 spec: 3.8.6 Texture Framebuffer Attachment).

for the most part we get the behaviour we want at a good performance. However, we are liable for any odd behaviour (such as seen in [Link Removed]).

We need to provide a proper, spec compliant, solution for depth reading.

A proper fix is to set GSupportsDepthFetchDuringDepthTest=false and draw depth to a float target and pass that as the aux depth texture (as happens when GSupportsDepthFetchDuringDepthTest == false). On devices that dont support float targets this could be rgb encoded. Additionally, we could consider an error in the gl rhi to detect this scenario.

run steps described in [Link Removed] and then set r.Mobile.ForceDepthResolve 0 and observe broken shadows.