148 lines
7.2 KiB
C++
148 lines
7.2 KiB
C++
/*******************************************************************************
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* The MIT License (MIT)
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*
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* Copyright (c) 2015 David Williams and Matthew Williams
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*******************************************************************************/
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namespace PolyVox
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{
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/**
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* This function fills a 3D array with ambient occlusion values computed by raycasting through the volume.
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* This approach to ambient occlusion is only appropriate for relatvely small volumes, otherwise it will
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* become very slow and consume a lot of memory. You will need to find a way to actually use the generated
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* ambient occlusion data, which might mean uploading it the the GPU as a volume texture or sampling on
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* the CPU using the vertex positions from your generated mesh.
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*
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* In practice we have not made much use of this implementation ourselves, so you may find it needs some
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* optimizations or improvements to be useful. It is likely that there are actually better approaches to
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* the ambient occlusion problem.
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*
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* \param volInput The volume to calculate the ambient occlusion for
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* \param[out] arrayResult The output of the calculator
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* \param region The region of the volume for which the occlusion should be calculated
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* \param fRayLength The length for each test ray
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* \param uNoOfSamplesPerOutputElement The number of samples to calculate the occlusion
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* \param isVoxelTransparentCallback A callback which takes a \a VoxelType and returns a \a bool whether the voxel is transparent
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*/
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template<typename VolumeType, typename IsVoxelTransparentCallback>
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void calculateAmbientOcclusion(VolumeType* volInput, Array<3, uint8_t>* arrayResult, const Region& region, float fRayLength, uint8_t uNoOfSamplesPerOutputElement, IsVoxelTransparentCallback isVoxelTransparentCallback)
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{
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//Make sure that the size of the volume is an exact multiple of the size of the array.
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if (region.getWidthInVoxels() % arrayResult->getDimension(0) != 0)
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{
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POLYVOX_THROW(std::invalid_argument, "Volume width must be an exact multiple of array width.");
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}
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if (region.getHeightInVoxels() % arrayResult->getDimension(1) != 0)
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{
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POLYVOX_THROW(std::invalid_argument, "Volume width must be an exact multiple of array height.");
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}
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if (region.getDepthInVoxels() % arrayResult->getDimension(2) != 0)
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{
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POLYVOX_THROW(std::invalid_argument, "Volume width must be an exact multiple of array depth.");
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}
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uint16_t uRandomUnitVectorIndex = 0;
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uint16_t uRandomVectorIndex = 0;
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uint16_t uIndexIncreament;
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//Our initial indices. It doesn't matter exactly what we set here, but the code below makes
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//sure they are different for different regions which helps reduce tiling patterns in the results.
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uRandomUnitVectorIndex += region.getLowerX() + region.getLowerY() + region.getLowerZ();
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uRandomVectorIndex += region.getLowerX() + region.getLowerY() + region.getLowerZ();
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//This value helps us jump around in the array a bit more, so the
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//nth 'random' value isn't always followed by the n+1th 'random' value.
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uIndexIncreament = 1;
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const int iRatioX = region.getWidthInVoxels() / arrayResult->getDimension(0);
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const int iRatioY = region.getHeightInVoxels() / arrayResult->getDimension(1);
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const int iRatioZ = region.getDepthInVoxels() / arrayResult->getDimension(2);
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const float fRatioX = iRatioX;
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const float fRatioY = iRatioY;
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const float fRatioZ = iRatioZ;
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const Vector3DFloat v3dRatio(fRatioX, fRatioY, fRatioZ);
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const float fHalfRatioX = fRatioX * 0.5f;
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const float fHalfRatioY = fRatioY * 0.5f;
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const float fHalfRatioZ = fRatioZ * 0.5f;
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const Vector3DFloat v3dHalfRatio(fHalfRatioX, fHalfRatioY, fHalfRatioZ);
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const Vector3DFloat v3dOffset(0.5f, 0.5f, 0.5f);
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//This loop iterates over the bottom-lower-left voxel in each of the cells in the output array
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for (uint16_t z = region.getLowerZ(); z <= region.getUpperZ(); z += iRatioZ)
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{
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for (uint16_t y = region.getLowerY(); y <= region.getUpperY(); y += iRatioY)
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{
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for (uint16_t x = region.getLowerX(); x <= region.getUpperX(); x += iRatioX)
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{
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//Compute a start position corresponding to
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//the centre of the cell in the output array.
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Vector3DFloat v3dStart(x, y, z);
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v3dStart -= v3dOffset;
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v3dStart += v3dHalfRatio;
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//Keep track of how many rays did not hit anything
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uint8_t uVisibleDirections = 0;
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for (int ct = 0; ct < uNoOfSamplesPerOutputElement; ct++)
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{
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//We take a random vector with components going from -1 to 1 and scale it to go from -halfRatio to +halfRatio.
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//This jitter value moves our sample point from the centre of the array cell to somewhere else in the array cell
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Vector3DFloat v3dJitter = randomVectors[(uRandomVectorIndex += (++uIndexIncreament)) % 1019]; //Prime number helps avoid repetition on successive loops.
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v3dJitter *= v3dHalfRatio;
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const Vector3DFloat v3dRayStart = v3dStart + v3dJitter;
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Vector3DFloat v3dRayDirection = randomUnitVectors[(uRandomUnitVectorIndex += (++uIndexIncreament)) % 1021]; //Different prime number.
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v3dRayDirection *= fRayLength;
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AmbientOcclusionCalculatorRaycastCallback<VolumeType, IsVoxelTransparentCallback> ambientOcclusionCalculatorRaycastCallback(isVoxelTransparentCallback);
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RaycastResult result = raycastWithDirection(volInput, v3dRayStart, v3dRayDirection, ambientOcclusionCalculatorRaycastCallback);
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// Note - The performance of this could actually be improved it we exited as soon
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// as the ray left the volume. The raycast test has an example of how to do this.
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if (result == RaycastResults::Completed)
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{
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++uVisibleDirections;
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}
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}
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float fVisibility;
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if (uNoOfSamplesPerOutputElement == 0)
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{
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//The user might request zero samples (I've done this in the past while debugging - I don't want to
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//wait for ambient occlusion but I do want as valid result for rendering). Avoid the divide by zero.
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fVisibility = 1.0f;
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}
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else
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{
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fVisibility = static_cast<float>(uVisibleDirections) / static_cast<float>(uNoOfSamplesPerOutputElement);
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POLYVOX_ASSERT((fVisibility >= 0.0f) && (fVisibility <= 1.0f), "Visibility value out of range.");
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}
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(*arrayResult)(z / iRatioZ, y / iRatioY, x / iRatioX) = static_cast<uint8_t>(255.0f * fVisibility);
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}
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}
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}
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}
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}
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