35 lines
1.2 KiB
Plaintext
35 lines
1.2 KiB
Plaintext
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//Inputs
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float dt; // user-specified time step
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float velScale; // user-specified velocity scalar (flow rate)
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float4 dxdy; // (pixel width, pixel height, 1 / dx, 1 / dy) precomputed
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float4 DomainRes; // (xRes, yRes, 1 / xRes, 1 / yRes)
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Texture2D<float4> InputTex; // Texture to advect
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Texture2D<float2> VelocityTex; // m/s
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//output
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RWTexture2D<float4> OutputTex;
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float4 bilinearSample(Texture2D<float4> t, float2 coord) {
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float2 f = frac(coord);
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float4 tl = t[(uint2)coord];
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float4 tr = t[uint2(coord.x + 1, coord.y)];
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float4 bl = t[uint2(coord.x, coord.y + 1)];
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float4 br = t[uint2(coord.x + 1, coord.y + 1)];
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float4 ta = lerp(tl, tr, f.x);
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float4 tb = lerp(bl, br, f.x);
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return lerp(ta, tb, f.y);
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}
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#pragma kernel Advect
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[numthreads(1, 1, 1)]
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void Advect(uint3 id : SV_DispatchThreadID) {
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// need to scale the velocity by pixel size (in world coordinates) since we are actually operating by pixel index
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float2 vel = velScale * VelocityTex[id.xy].xy * dxdy.zw;
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// backtraced coordinates
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float2 xy = clamp(float2((float)id.x, (float)id.y) - (dt * vel), 0.0f, DomainRes.xy + float2(1.0f, 1.0f));
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OutputTex[id.xy] = bilinearSample(InputTex, xy);
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}
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