adding surface extraction pass

res/shaders/Extract.slang

@@ -0,0 +1,47 @@
+import FluidGridData;
+
+struct Parameter
+{
+    float iso;
+    FluidGridData<float> density;
+    RWStructuredBuffer<float3> vertices;
+    RWStructuredBuffer<uint> indices;
+    RWStructuredBuffer<uint> surfaceCount;
+    RWStructuredBuffer<uint> vertexCount;
+};
+ParameterBlock<Parameter> params;
+
+float getDensity(uint x, uint y, uint z)
+{
+    return params.density[x + gridSize.x * y + gridSize.x * gridSize.y * z];
+}
+
+[shader("compute")]
+[numthreads(32, 8, 1)]
+void main(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    uint x = dispatchThreadID.x+1;
+    uint y = dispatchThreadID.y+1;
+    uint z = dispatchThreadID.z+1;
+    FluidGridData<float> density = params.density;
+    if(x >= gridSize.x-3 || y >= gridSize.y-3 || z >= gridSize.z-3) return;
+
+    float phi[8] = {
+        getDensity(x, y, z),
+        getDensity(x + 1, y, z),
+        getDensity(x, y + 1, z),
+        getDensity(x + 1, y + 1, z),
+        getDensity(x, y, z + 1),
+        getDensity(x + 1, y, z + 1),
+        getDensity(x, y + 1, z + 1),
+        getDensity(x + 1, y + 1, z + 1)
+    };
+
+    uint cubeIndex = 0;
+    for (uint i = 0; i < 8; ++i) {
+        if (phi[i] < params.iso) {
+            cubeIndex |= (1 << i);
+        }
+    }
+    if(cubeIndex == 0 || cubeIndex == 255) return;
+}

res/shaders/Render.slang

@@ -27,6 +27,6 @@ float4 fragmentMain(VertexOut input) : SV_Target
     FluidGridData<float> density = params.density;
     int x = int(input.uv.x * (gridSize.x - 2) + 1);
     int y = int(input.uv.y * (gridSize.y - 2) + 1);
-    float d = density[x, y, 0];
+    float d = density[x, y, 1];
     return float4(d, d, d, 1);
 }