Vulkan: Sampling Depth Texture on Forward Mobile with MSAA is corrupted

[SeanH-CB]

Godot version

4.1.1.stable

System information

Windows 10, Vulkan, NVidia GTX 1060 Driver Version 536.23

Issue description

On Forward Mobile having a Shader Material which samples the Depth Texture and having MSAA X2, X4, X8 enabled, causes the Depth Textures sampled data to be corrupted. Most likely its missing an MSAA Resolve before being bound.

Mobile:

Forward+

Steps to reproduce

• New 3D Project
• Set Renderer to Mobile
• Set 3D Anti-Aliasing in project settings to MSAA X2
• Create a MeshInstance3D
• Create a Shader Material which samples the Depth Texture
• See Depth Values are not what you'd expect

Minimal reproduction project

Depth Readback Repo.zip

[SeanH-CB]

#60255
Seems like its a similar issue which was closed off as not reproducible

[Calinou]

• Related to Vulkan: Normal buffer view broken when using MSAA on NVIDIA GPUs #62955.

cc @BastiaanOlij

[BastiaanOlij]

This is because the subpass system only has resolve for color buffers implemented. So the depth buffer isn't resolved and thus the buffer you're reading from is never properly populated.

I have a fix for this: #78598

But it relies on an extension that hasn't got enough coverage. I'm still looking into a fallback approach that works