import FluidGridData;

struct Params {
    // read-only
    FluidGridData<float> velocityX;
    // read-only
    FluidGridData<float> velocityY;
    // read-only
    FluidGridData<float> velocityZ;
    // read-write
    FluidGridData<float> divergence;
    // read-write
    FluidGridData<float> pressure;
};
ParameterBlock<Params> params;

[shader("compute")]
[numthreads(32, 8, 1)]
void computeDivergence(uint3 dispatchThreadID: SV_DispatchThreadID) {
    FluidGridData<float> velocityX = params.velocityX;
    FluidGridData<float> velocityY = params.velocityY;
    FluidGridData<float> velocityZ = params.velocityZ;
    FluidGridData<float> divergence = params.divergence;
    FluidGridData<float> pressure = params.pressure;

    int x = dispatchThreadID.x + 1;
    int y = dispatchThreadID.y + 1;
    int z = dispatchThreadID.z + 1;
    if (x >= gridParams.gridSize.x - 1 || y >= gridParams.gridSize.y - 1 || z >= gridParams.gridSize.z - 1)
        return;

    divergence[x, y, z] = -0.5f * (velocityX[x + 1, y, z] - velocityX[x - 1, y, z] + velocityY[x, y + 1, z] - velocityY[x, y - 1, z] + velocityZ[x, y, z + 1] - velocityZ[x, y, z - 1]);
    pressure[x, y, z] = 0;
}