Trying to add fluid simulation

res/shaders/fluid/SignedDistance.slang

@@ -0,0 +1,65 @@
+import FluidGridData;
+
+struct Params
+{
+    float dtau;
+    // read-write: phi being reinitialized
+    FluidGridData<float> phi;
+    // read-only: snapshot of phi before reinitialization (for sign)
+    FluidGridData<float> phi0;
+};
+ParameterBlock<Params> params;
+
+// Smooth sign function to avoid discontinuity at zero
+float smoothSign(float x, float dx)
+{
+    return x / sqrt(x * x + dx * dx);
+}
+
+[shader("compute")]
+[numthreads(32, 8, 1)]
+void reinitialize(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    uint x = dispatchThreadID.x + 1;
+    uint y = dispatchThreadID.y + 1;
+    uint z = dispatchThreadID.z + 1;
+    FluidGridData<float> phi = params.phi;
+    FluidGridData<float> phi0 = params.phi0;
+    if(x >= gridSize.x - 1 || y >= gridSize.y - 1 || z >= gridSize.z - 1) return;
+
+    float dtau = params.dtau;
+    float dx = 1.0f;
+
+    // Current value and original sign
+    float p = phi[x, y, z];
+    float s = smoothSign(phi0[x, y, z], dx);
+
+    // Upwind finite differences for |grad phi|
+    // Forward and backward differences
+    float dxp = phi[x + 1, y, z] - p;
+    float dxm = p - phi[x - 1, y, z];
+    float dyp = phi[x, y + 1, z] - p;
+    float dym = p - phi[x, y - 1, z];
+    float dzp = phi[x, y, z + 1] - p;
+    float dzm = p - phi[x, y, z - 1];
+
+    // Godunov upwind scheme
+    float gradPhi;
+    if (s > 0)
+    {
+        float ax = max(max(dxm, 0.0f), -min(dxp, 0.0f));
+        float ay = max(max(dym, 0.0f), -min(dyp, 0.0f));
+        float az = max(max(dzm, 0.0f), -min(dzp, 0.0f));
+        gradPhi = sqrt(ax * ax + ay * ay + az * az) / dx;
+    }
+    else
+    {
+        float ax = max(-min(dxm, 0.0f), max(dxp, 0.0f));
+        float ay = max(-min(dym, 0.0f), max(dyp, 0.0f));
+        float az = max(-min(dzm, 0.0f), max(dzp, 0.0f));
+        gradPhi = sqrt(ax * ax + ay * ay + az * az) / dx;
+    }
+
+    // Update: push |grad phi| toward 1
+    phi[x, y, z] = p - dtau * s * (gradPhi - 1.0f);
+}