Question Need some help doing manual depth testing

Unity 2021.3.15 LTS, URP

I'm trying to implement manual depth testing in a shader, where items are being rendered with ZWrite Off and using CommandBuffer.DrawMesh(). The draw order is random and cannot be changed. I have created a rendertexture of type R16G16_UNORM to which I write to and read from. Here is a gist of the render loop:

Code (CSharp):

1.  buffer.SetRenderTarget(_frameBuffer1, 0, CubemapFace.Unknown, -1);
2.                 buffer.ClearRenderTarget(true, true, Color.black);
3.                 buffer.SetRenderTarget(
4.                     new RenderTargetIdentifier[] { renderingData.cameraData.renderer.cameraColorTarget, _frameBuffer1 },
5.                     renderingData.cameraData.renderer.cameraDepthTarget, 0, CubemapFace.Unknown, -1);
6.  
7.                 for(int i = 0; i < itemList.Count; ++i)
8.                 {
9.                     var item = itemList[i];
10.                     item.ObjectRenderer.sharedMaterial.SetTexture(DepthLut, _frameBuffer1);
11.  
12.                     buffer.DrawMesh(item.ObjectRenderer.item.ObjectRenderer.sharedMaterial);
13.                 }
14.  

and the shader fragment looks like:

Code (CSharp):

1.             struct PixelS
2.             {
3.                 float4 target0 : SV_Target0;
4.                 float4 target1 : SV_Target1;
5.             };
6.            
7.             PixelS SpriteFrag(v2f IN)
8.             {
9.                 PixelS val;
10.                
11.                 float2 screenUv = IN.screenPos.xy / IN.screenPos.w; //screen uvs
12.                 float depth = IN.depth; //clip.z / clip.w
13.  
14.                 fixed4 d = tex2D(_DepthLut, screenUv.xy);
15.                
16.                 val.target0 = d; //to test value
17.                 val.target1 = float4( 0., depth > d.y ? depth : d.y, 0., 0. );
18.                
19.                 return val;
20.             }

The objects that are rendered later appear on top even if they are behind, so the comparison in the shader doesnt seem to be taking place. I'm constrained not using a depth buffer here. Any ideas what I'm doing wrong and what I can do?

 

Manual depth testing is not as easy as you think

- You can't read from a render target that you are currently rendering to
- You *can* use a RWTexture instead but that comes with some problems to:
-- Slow because you don't get early-z rejection. This means, you'll be shading much more pixels than usually
-- Multiple triangles are shaded in parallel. You have to use atomic writes.

It might be better to make a copy of your depth buffer and bind that instead.

Just some advice from one monkey to another

 

Yep I guess Ill have to bind another depth target