mirror of https://bitbucket.org/CPMADevs/cnq3
85 lines
3.5 KiB
HLSL
85 lines
3.5 KiB
HLSL
/*
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===========================================================================
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Copyright (C) 2024 Gian 'myT' Schellenbaum
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This file is part of Challenge Quake 3 (CNQ3).
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Challenge Quake 3 is free software; you can redistribute it
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and/or modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of the License,
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or (at your option) any later version.
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Challenge Quake 3 is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with Challenge Quake 3. If not, see <https://www.gnu.org/licenses/>.
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===========================================================================
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*/
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// volumetric lighting: raymarch froxels
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#include "common.hlsli"
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#include "scene_view.h.hlsli"
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cbuffer RootConstants
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{
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uint scatterTextureIndex;
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uint resolveTextureIndex;
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uint materialTextureBIndex;
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}
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[numthreads(8, 8, 1)]
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void cs(uint3 id : SV_DispatchThreadID)
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{
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RWTexture3D<float4> scatterTexture = ResourceDescriptorHeap[scatterTextureIndex];
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uint3 textureSize = GetTextureSize(scatterTexture);
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if(any(id.xy >= textureSize.xy))
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{
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return;
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}
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// Even if the extinction coefficient is constant all along a given line segment of length Z,
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// the transmittance is different at every point.
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// We compute the final scatter/emissive using an analytical solution like Frostbite does.
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// Integral(T(x) * dx) == Integral(e^(-extinction*x) * dZ) [0 to Z]
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// == [e^(-extinction*x) / (-extinction)] [0 to Z]
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// == (-1 / extinction) * [e^(-Z*extinction)] [0 to Z]
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// == (-1 / extinction) * [T(Z)] [0 to Z]
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// == (-1 / extinction) * (T(Z) - T(0))
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// == (-1 / extinction) * (T(Z) - 1)
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// == (1 / extinction) * (1 - T(Z))
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// == (1 - T(Z)) / extinction
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// The scatter/emissive coefficients are considered uniform in each froxel.
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// They are therefore constants that can be pulled out of the integral, hence their omission.
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SceneView scene = GetSceneView();
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RWTexture3D<float4> resolveTexture = ResourceDescriptorHeap[resolveTextureIndex];
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RWTexture3D<float4> materialTextureB = ResourceDescriptorHeap[materialTextureBIndex];
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uint3 index0 = uint3(id.xy, 0);
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float3 tc0 = (float3(index0) + float3(0.5, 0.5, 0)) / textureSize; // near edge of first voxel
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float3 prevPosition = scene.FroxelTCToWorldSpace(tc0, float3(textureSize));
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float3 accumScatter = float3(0, 0, 0);
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float accumTrans = 1.0;
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for(uint d = 0; d < textureSize.z; d++)
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{
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uint3 index = uint3(id.xy, d);
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float3 tc = (float3(index) + float3(0.5, 0.5, 1)) / textureSize; // far edge of current voxel
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float4 froxelScatterExt = scatterTexture[index];
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float3 froxelEmissive = materialTextureB[index].rgb;
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float3 froxelScatter = froxelScatterExt.rgb;
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float froxelExtinction = froxelScatterExt.a;
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float3 currPosition = scene.FroxelTCToWorldSpace(tc, float3(textureSize));
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float depthStep = distance(currPosition, prevPosition);
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float froxelTrans = Transmittance(depthStep, froxelExtinction);
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float froxelTransInteg = (1.0 - froxelTrans) / (froxelExtinction == 0.0 ? 1.0 : froxelExtinction);
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accumScatter += (accumTrans * froxelTransInteg) * (froxelScatter + froxelEmissive);
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accumTrans *= froxelTrans;
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resolveTexture[index] = float4(accumScatter, accumTrans);
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prevPosition = currPosition;
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}
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}
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