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hair particle: frustum culling runs only once per-strand instead of e…
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…very segment
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@turanszkij
turanszkij committed Feb 20, 2025
1 parent 849e71a commit 4f579e9
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Showing 2 changed files with 46 additions and 49 deletions.
93 changes: 45 additions & 48 deletions WickedEngine/shaders/hairparticle_simulateCS.hlsl
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,11 @@ void main(uint3 DTid : SV_DispatchThreadID, uint3 Gid : SV_GroupID, uint groupIn
return;

const bool regenerate_frame = xHairFlags & HAIR_FLAG_REGENERATE_FRAME;
const uint gfx_vertexcount_per_strand = (xHairSegmentCount * 2 + 2) * xHairBillboardCount;
const uint gfx_indexcount_per_strand = 6 * xHairBillboardCount * xHairSegmentCount;
const uint index0 = DTid.x * gfx_indexcount_per_strand;
const uint vertexID0 = DTid.x * gfx_vertexcount_per_strand;
uint v0 = vertexID0;

ShaderGeometry geometry = HairGetGeometry();

Expand Down Expand Up @@ -69,12 +74,10 @@ void main(uint3 DTid : SV_DispatchThreadID, uint3 Gid : SV_GroupID, uint groupIn
g = 1 - g;
}
float2 bary = float2(f, g);

const float4x4 worldMatrix = xHairTransform.GetMatrix();

// compute final surface position on triangle from barycentric coords:
float3 position = attribute_at_bary(pos0, pos1, pos2, bary);
position = mul(xHairBaseMeshUnormRemap.GetMatrix(), float4(position, 1)).xyz;
position = mul(xHairBaseMeshUnormRemap.GetMatrix(), float4(position, 1)).xyz; // position UNORM -> FLOAT
half3 target = normalize(attribute_at_bary(nor0, nor1, nor2, bary));
target = normalize(mul(xHairTransform.GetMatrixAdjoint(), target));
half3 tangent = normalize(mul(half3(hemispherepoint_cos(rng.next_float(), rng.next_float()).xy, 0), get_tangentspace(target)));
Expand All @@ -84,29 +87,56 @@ void main(uint3 DTid : SV_DispatchThreadID, uint3 Gid : SV_GroupID, uint groupIn
const uint currentFrame = uint(noise_gradient_3D(position * xHairUniformity) * 1000) % xHairAtlasRectCount;
const HairParticleAtlasRect atlas_rect = xHairAtlasRects[currentFrame];

// Identifies the hair strand root particle:
const uint strandID = DTid.x * xHairSegmentCount;

// Transform particle by the emitter object matrix:
float3 base = mul(worldMatrix, float4(position.xyz, 1)).xyz;
float3 base = mul(xHairTransform.GetMatrix(), float4(position.xyz, 1)).xyz;

float3 diff = GetCamera().position - base;
const float distsq = dot(diff, diff);
const bool distance_culled = distsq > sqr(xHairViewDistance);

// Frustum culling the whole strand at once:
// intentionally overestimated, to not disappear as soon in different views (shadow map, etc)
ShaderSphere sphere;
sphere.center = base;
sphere.radius = xHairLength;
//draw_sphere(sphere.center, sphere.radius);
const bool visible = !distance_culled && GetCamera().frustum.intersects(sphere);

// Optimization: reduce to 1 atomic operation per wave
const uint waveAppendCount = WaveActiveCountBits(visible);
uint waveOffset;
if (WaveIsFirstLane() && waveAppendCount > 0)
{
InterlockedAdd(indirectBuffer[0].IndexCountPerInstance, waveAppendCount * gfx_indexcount_per_strand, waveOffset);
}
waveOffset = WaveReadLaneFirst(waveOffset);

// Append visible indices:
if (visible)
{
uint prevCount = waveOffset + WavePrefixSum(gfx_indexcount_per_strand);
uint i0 = index0;
uint ii0 = prevCount;
for (uint segmentID = 0; segmentID < xHairSegmentCount; ++segmentID)
{
for (uint billboardID = 0; billboardID < xHairBillboardCount; ++billboardID)
{
culledIndexBuffer[ii0++] = i0++;
culledIndexBuffer[ii0++] = i0++;
culledIndexBuffer[ii0++] = i0++;
culledIndexBuffer[ii0++] = i0++;
culledIndexBuffer[ii0++] = i0++;
culledIndexBuffer[ii0++] = i0++;
}
}
}

half len = lerp(1, rng.next_float(), saturate(xHairRandomness)) * strand_length;
len *= xHairLength;
len *= atlas_rect.size;
len /= (half)xHairSegmentCount;
const float2 frame = float2(atlas_rect.aspect * xHairAspect * xHairSegmentCount, 1) * len * 0.5;
const float segment_radius = max(frame.x, frame.y);

const uint gfx_vertexcount_per_strand = (xHairSegmentCount * 2 + 2) * xHairBillboardCount;
const uint gfx_indexcount_per_particle = 6 * xHairBillboardCount;
const uint gfx_indexcount_per_strand = gfx_indexcount_per_particle * xHairSegmentCount;
const uint index0 = DTid.x * gfx_indexcount_per_strand;
const uint vertexID0 = DTid.x * gfx_vertexcount_per_strand;
uint v0 = vertexID0;

//draw_line(base, base + tangent, float4(1, 0, 0, 1));
//draw_line(base, base + target, float4(0, 1, 0, 1));
Expand Down Expand Up @@ -184,7 +214,7 @@ void main(uint3 DTid : SV_DispatchThreadID, uint3 Gid : SV_GroupID, uint groupIn
for (uint segmentID = 0; segmentID < xHairSegmentCount; ++segmentID)
{
// Identifies the hair strand segment particle:
const uint particleID = strandID + segmentID;
const uint particleID = DTid.x * xHairSegmentCount + segmentID;

if (regenerate_frame)
{
Expand Down Expand Up @@ -380,39 +410,6 @@ void main(uint3 DTid : SV_DispatchThreadID, uint3 Gid : SV_GroupID, uint groupIn
}
}

// Frustum culling:
ShaderSphere sphere;
sphere.center = (base + tail_next) * 0.5;
sphere.radius = segment_radius;
//draw_sphere(sphere.center, sphere.radius);

const bool visible = !distance_culled && GetCamera().frustum.intersects(sphere);

// Optimization: reduce to 1 atomic operation per wave
const uint waveAppendCount = WaveActiveCountBits(visible);
uint waveOffset;
if (WaveIsFirstLane() && waveAppendCount > 0)
{
InterlockedAdd(indirectBuffer[0].IndexCountPerInstance, waveAppendCount * gfx_indexcount_per_particle, waveOffset);
}
waveOffset = WaveReadLaneFirst(waveOffset);

if (visible)
{
uint prevCount = waveOffset + WavePrefixSum(gfx_indexcount_per_particle);
uint i0 = particleID * gfx_indexcount_per_particle;
uint ii0 = prevCount;
for (uint billboardID = 0; billboardID < xHairBillboardCount; ++billboardID)
{
culledIndexBuffer[ii0++] = i0++;
culledIndexBuffer[ii0++] = i0++;
culledIndexBuffer[ii0++] = i0++;
culledIndexBuffer[ii0++] = i0++;
culledIndexBuffer[ii0++] = i0++;
culledIndexBuffer[ii0++] = i0++;
}
}

// Offset next segment root to current tip:
base = tail_next;
target = normal;
Expand Down
2 changes: 1 addition & 1 deletion WickedEngine/wiVersion.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@ namespace wi::version
// minor features, major updates, breaking compatibility changes
const int minor = 71;
// minor bug fixes, alterations, refactors, updates
const int revision = 684;
const int revision = 685;

const std::string version_string = std::to_string(major) + "." + std::to_string(minor) + "." + std::to_string(revision);

Expand Down

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