Question by sparkkhuang · Feb 24 at 03:19 AM · rendering shader programming gameplay compute shader hlsl

How to use the compute shader to sample the depth map under URP and calculate the corresponding world coordinates?

Here is my code, but the output is always weird.

compute shader:

 #pragma kernel WaterSplash
 
 struct Particle
 {
     float3 position;
     float lifetime;
     float showScale;
 };
 
 RWStructuredBuffer<Particle> particleBuffer;
 
 RWTexture2D<float4> DeptTex;
 
 float deltaTime;
 float width; 
 
 float4x4 vpMatrixInv;
 
 [numthreads(8,8,1)]
 void WaterSplash(uint3 id : SV_DispatchThreadID)
 {
     float dept = DeptTex[id.xy].r;
 
 #if defined(UNITY_REVERSED_Z)
     dept = 1 - dept;
 #endif
 
     float4 ndc = float4(id.x * 2 - 1, id.y * 2 - 1, dept * 2 - 1, 1);
 
     float4 worldPos = mul(vpMatrixInv, ndc);
     worldPos /= worldPos.w;
 
     int index = id.x * width + id.y;
 
     particleBuffer[index].position = float3(worldPos.x, worldPos.y, worldPos.z);
     particleBuffer[index].lifetime += deltaTime;
 
     if (particleBuffer[index].lifetime > 2)
     {
         particleBuffer[index].lifetime = 0;
     }
 
 
     particleBuffer[index].showScale = dept;
 }

C# pass parameter code :

     computeShader.SetMatrix("vpMatrixInv", vpMatrixMake());
 
     private Matrix4x4 vpMatrixMake()
     {
         Matrix4x4 projMat = GL.GetGPUProjectionMatrix(Camera.projectionMatrix, false);
         var vpMatrix = projMat * Camera.worldToCameraMatrix;
 
 
         //var vpMatrix = Camera.projectionMatrix * Camera.worldToCameraMatrix;
 
 
         return vpMatrix.inverse;
     }

     computeShader.SetTexture(mComputeShaderKernelID, "DeptTex", DepthRT);
     private void DepthMake()
     {
         RenderTexture tempRT;

         tempRT = RenderTexture.GetTemporary(width, height, 0, DepthRT.format);
         tempRT.filterMode = FilterMode.Point;

         Graphics.Blit(Shader.GetGlobalTexture("_CameraDepthTexture"), tempRT);

         Graphics.CopyTexture(tempRT, 0, 0, DepthRT, 0, 0);
     }

     width = Screen.width;
     height = Screen.height;
     computeShader.Dispatch(mComputeShaderKernelID, width / 8, height / 8, 1);

The calculated coordinates are always columnar, like: alt text