246 lines
9.7 KiB
Plaintext
246 lines
9.7 KiB
Plaintext
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//inputs
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Texture2D<float4> PrecipMask; //defines where rainfall will occur
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Texture2D<float> Collision; //defines texels we will "lock" for the simulation
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Texture2D<float> TerrainHeightPrev; //previous frame
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Texture2D<float2> WaterVelPrev; //water vel prev
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Texture2D<float> Hardness; //mineral hardness
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//Texture2D<float> HeightToScale; //curve mapping height -> scale
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RWTexture2D<float> TerrainHeight; //terrain heightmap
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RWTexture2D<float> Water; //water height
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RWTexture2D<float> WaterPrev; //water height prev
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RWTexture2D<float2> WaterVel; //water velocity
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RWTexture2D<float4> Flux; //current water flux (how much water is transferring to neighboring cells)
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RWTexture2D<float4> FluxPrev; //flux
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RWTexture2D<float> Sediment; //suspended sediment concentration (being transported by the water)
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RWTexture2D<float> SedimentPrev;
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RWTexture2D<float> Eroded; //how much sediment was eroded this frame
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float EffectScalar;
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float DT;
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float4 dxdy; //<dx, dy, 1 / dx, 1 / dy>
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#define DX dxdy.x
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#define DY dxdy.y
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#define INV_DX dxdy.z
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#define INV_DY dxdy.w
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float4 WaterTransportScalars; //(WaterLevelScale, precipRate, flowRate, evapRate)
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#define WATER_LEVEL_SCALE WaterTransportScalars.x
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#define PRECIP_RATE WaterTransportScalars.y
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#define FLOW_RATE WaterTransportScalars.z
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#define EVAP_RATE WaterTransportScalars.w
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float4 SedimentScalars; //(SedimentScale, Capacity, DissolveRate, DepositRate)
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#define SEDIMENT_SCALE SedimentScalars.x
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#define SEDIMENT_CAP SedimentScalars.y
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#define SEDIMENT_DISSOLVE_RATE SedimentScalars.z
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#define SEDIMENT_DEPOSIT_RATE SedimentScalars.w
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float4 RiverBedScalars; //(bedDissolveRate, bedDepositRate, bankDissolveRate, bankDepositRate)
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#define RIVER_BED_DISSOLVE_RATE RiverBedScalars.x
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#define RIVER_BED_DEPOSIT_RATE RiverBedScalars.y
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#define RIVER_BANK_DISSOLVE_RATE RiverBedScalars.z
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#define RIVER_BANK_DEPOSIT_RATE RiverBedScalars.w
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float4 texDim; //the dimensions of all of our textures (they must all be the same dimensions)
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float3 terrainDim; //the dimensions of the terrain in world units
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//float4 HeightToScaleRange; //(min, max, ?, ?)
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uint4 getSafeNeighbors(uint2 coord) {
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return uint4(
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(coord.x < (uint)(texDim[0] - 1)) ? coord.x + 1 : coord.x, //right index
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(coord.x > 0) ? (uint)(coord.x - 1) : coord.x, //left index
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(coord.y < (uint)(texDim[1] - 1)) ? coord.y + 1 : coord.y, //bottom index
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(coord.y > 0) ? (uint)(coord.y - 1) : coord.y //top index
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);
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}
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#define RIGHT(c) (c.x)
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#define LEFT(c) (c.y)
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#define BOTTOM(c) (c.z)
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#define TOP(c) (c.w)
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float3 computeNormal(uint2 coord) {
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//This is faster, but doesn't get recomputed every iteration.
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//float3 n = 2.0f * (SurfaceNormal[coord] - float3(0.5f, 0.5f, 0.5f));
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//n = normalize(n);
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//this is more accurate, and probably is better at removing rectilinear artifacts, since we are sampling 8 neighbors
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//but... slower
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uint4 nidx = getSafeNeighbors(coord);
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float dzdx = ((TerrainHeightPrev[uint2(RIGHT(nidx), BOTTOM(nidx))] + 2 * TerrainHeightPrev[uint2(RIGHT(nidx), coord.y)] + TerrainHeightPrev[uint2(RIGHT(nidx), TOP(nidx))]) -
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(TerrainHeightPrev[uint2(LEFT(nidx), BOTTOM(nidx))] + 2 * TerrainHeightPrev[uint2(LEFT(nidx), coord.y)] + TerrainHeightPrev[uint2(LEFT(nidx), TOP(nidx))])) / 8.0f;
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float dzdy = ((TerrainHeightPrev[uint2(LEFT(nidx), TOP(nidx))] + 2 * TerrainHeightPrev[uint2(coord.x, TOP(nidx))] + TerrainHeightPrev[uint2(RIGHT(nidx), TOP(nidx))]) -
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(TerrainHeightPrev[uint2(LEFT(nidx), BOTTOM(nidx))] + 2 * TerrainHeightPrev[uint2(coord.x, BOTTOM(nidx))] + TerrainHeightPrev[uint2(RIGHT(nidx), BOTTOM(nidx))])) / 8.0f;
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float m = length(float2(dzdx, dzdy));
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return normalize(float3(dzdx, m, dzdy));
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}
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float4 simulateFlux(uint2 coord, float cellArea) {
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float h = TerrainHeightPrev[coord] + WaterPrev[coord];
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float tileHeight = terrainDim.y;
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uint4 nidx = getSafeNeighbors(coord); //indices of neighbor cells, packed to a uint4
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// 1.21 Gigawatts?!?!?
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float fluxCapacitance = (DT * FLOW_RATE) / cellArea;
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//left
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float4 outFlux;
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float dh = tileHeight * (h - (TerrainHeightPrev[uint2(LEFT(nidx), coord.y)] + WaterPrev[uint2(LEFT(nidx), coord.y)]));
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LEFT(outFlux) = max(0.0f, LEFT(FluxPrev[coord]) + dh * fluxCapacitance);
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//right
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dh = tileHeight * (h - (TerrainHeightPrev[uint2(RIGHT(nidx), coord.y)] + WaterPrev[uint2(RIGHT(nidx), coord.y)]));
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RIGHT(outFlux) = max(0.0f, RIGHT(FluxPrev[coord]) + dh * fluxCapacitance);
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//top
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dh = tileHeight * (h - (TerrainHeightPrev[uint2(coord.x, TOP(nidx))] + WaterPrev[uint2(coord.x, TOP(nidx))]));
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TOP(outFlux) = max(0.0f, TOP(FluxPrev[coord]) + dh * fluxCapacitance);
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//bottom
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dh = tileHeight * (h - (TerrainHeightPrev[uint2(coord.x, BOTTOM(nidx))] + WaterPrev[uint2(coord.x, BOTTOM(nidx))]));
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BOTTOM(outFlux) = max(0.0f, BOTTOM(FluxPrev[coord]) + dh * fluxCapacitance);
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return outFlux;
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}
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void simulateWaterVelocity(uint2 coord, float cellArea) {
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uint4 nidx = getSafeNeighbors(coord);
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//use flux (instead of FluxPrev) here because we've already computed this for this frame
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float inFlow = RIGHT(Flux[uint2(LEFT(nidx), coord.y)]) +
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LEFT(Flux[uint2(RIGHT(nidx), coord.y)]) +
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TOP(Flux[uint2(coord.x, BOTTOM(nidx))]) +
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BOTTOM(Flux[uint2(coord.x, TOP(nidx))]);
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float outFlow = LEFT(Flux[coord]) + RIGHT(Flux[coord]) + TOP(Flux[coord]) + BOTTOM(Flux[coord]);
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float dV = DT * (inFlow - outFlow);
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float waterOld = WaterPrev[coord] / WATER_LEVEL_SCALE;
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float waterNew = waterOld + dV / cellArea;
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//update velocities
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float waterAvg = 0.5f * (waterOld + waterNew);
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float2 newWaterVel;
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waterAvg = 1.0f / waterAvg; //possible NaN here if waterAvg is zero, but don't seem to be hitting it...
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newWaterVel.x = waterAvg * 0.5f * (LEFT(Flux[uint2(LEFT(nidx), coord.y)]) - RIGHT(Flux[coord]) - RIGHT(Flux[uint2(RIGHT(nidx), coord.y)]) + LEFT(Flux[coord])) / DX;
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newWaterVel.y = waterAvg * 0.5f * (BOTTOM(Flux[uint2(coord.x, TOP(nidx))]) - TOP(Flux[coord]) - TOP(Flux[uint2(coord.x, BOTTOM(nidx))]) + BOTTOM(Flux[coord])) / DY;
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Water[coord] = WATER_LEVEL_SCALE * max(0.0f, waterNew);
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WaterVel[coord] = newWaterVel;
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}
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#pragma kernel SimulateWaterFlow
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[numthreads(8, 8, 1)]
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void SimulateWaterFlow(uint3 id : SV_DispatchThreadID)
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{
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uint2 coord = id.xy;
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//rainfall
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float rainfall = PRECIP_RATE * DT;
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float evaporated = EVAP_RATE * DT;
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float cellArea = (DX * DY);
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Flux[coord] = simulateFlux(coord, cellArea);
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simulateWaterVelocity(coord, cellArea);
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Water[coord] = WATER_LEVEL_SCALE * max(WaterPrev[coord] / WATER_LEVEL_SCALE + rainfall - evaporated, 0.0f);
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}
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//
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// Hydraulic Erosion
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//
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void simulateErosion(uint2 coord, out float newSediment, out float newHeight) {
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float cellArea = dxdy.x * dxdy.y;
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float kc = cellArea * SEDIMENT_CAP;
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float h = TerrainHeightPrev[coord];
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float s = SedimentPrev[coord];// / SEDIMENT_SCALE;
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float w = WaterPrev[coord] / WATER_LEVEL_SCALE;
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float3 n = computeNormal(coord);
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float slopeFactor = saturate(dot(n, float3(0.0f, 1.0f, 0.0f)));
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float slopeDissolveScalar = lerp(RiverBedScalars[2], RiverBedScalars[0], slopeFactor);
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float slopeDepositScalar = lerp(RiverBedScalars[3], RiverBedScalars[1], slopeFactor);
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float flowSpeed = sqrt(WaterVel[coord].x * WaterVel[coord].x + WaterVel[coord].y * WaterVel[coord].y);
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// calculate how much sediment we will dissolve
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// the cos function here is just to blend between the maximum dissolve rate (when no sediment is suspended)
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// and zero, when the suspended sediment amount equals the sediment capacity
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float hardness = 0.0f;// Hardness[coord]; //TODO
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float effectiveDissolveRate = saturate(hardness) * slopeDissolveScalar * flowSpeed * SEDIMENT_DISSOLVE_RATE * cos(0.5f * 3.14159f * (s / kc));
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float dissolved = clamp(DT * effectiveDissolveRate, 0.0f, kc);
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//calculate how much sediment we will deposit
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float effectiveDepositRate = slopeDepositScalar * (1.0f / max(flowSpeed, 0.05f)) * SEDIMENT_DEPOSIT_RATE;
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float deposited = DT * effectiveDepositRate;
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newSediment = max(s + EffectScalar * (dissolved - deposited), 0.0f);
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newHeight = max(h + EffectScalar * (deposited - dissolved), 0.0f);
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}
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//TODO: general-purpose advection kernel? (use Advection compute shader instead, for consistency)
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void simulateSedimentTransport(uint2 coord, out float transportedSediment) {
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float WaterSpeed = 1.0f; //user param?
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float speed = WaterSpeed * DT;
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float2 vel = WaterVel[coord].xy * dxdy.xy;
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float x = clamp((float)coord.x - (speed * vel.x), 0.0f, texDim[0] - 1);
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float y = clamp((float)coord.y - (speed * vel.y), 0.0f, texDim[1] - 1);
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uint2 uv0 = uint2((uint)x, (uint)y);
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uint2 uv1 = uv0 + uint2(1, 1);
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// remainder values, used for blending between voxels
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// TODO: optimize by using free pixel interpolation in pixel shader?
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float s1 = (x - (float)uv0.x) / texDim[0];
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float s0 = 1.0f - s1;
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float t1 = (y - (float)uv0.y) / texDim[1];
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float t0 = 1.0f - t1;
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// sample from 4 backtraced voxels, in proportions based on where the exact backtraced position landed
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// essentially doing bilinear interpolation here
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transportedSediment = (s0 * (t0 * SedimentPrev[uv0] + t1 * SedimentPrev[uint2(uv0.x, uv1.y)]) +
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s1 * (t1 * SedimentPrev[uint2(uv1.x, uv0.x)] + t1 * SedimentPrev[uv1]));// / SEDIMENT_SCALE;
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}
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#pragma kernel HydraulicErosion
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[numthreads(8, 8, 1)]
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void HydraulicErosion(uint3 id : SV_DispatchThreadID)
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{
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float dissolvedSediment = 0.0f;
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float transportedSediment = 0.0f;
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float newHeight = 0.0f;
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simulateErosion(id.xy, dissolvedSediment, newHeight);
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simulateSedimentTransport(id.xy, transportedSediment); //doesn't appear to have a visual result
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//TODO: Figure out why these values are so screwy
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//Eroded[id.xy] = Eroded[id.xy] + 100.0f * max(TerrainHeightPrev[id.xy] - newHeight, 0.0f);
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Sediment[id.xy] = /*SEDIMENT_SCALE * */(dissolvedSediment + transportedSediment);
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TerrainHeight[id.xy] = newHeight;
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}
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