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@@ -73,6 +73,10 @@ void btHeightfieldTerrainShape::initialize(
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m_useZigzagSubdivision = false;
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m_upAxis = upAxis;
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m_localScaling.setValue(btScalar(1.), btScalar(1.), btScalar(1.));
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+ m_vboundsGrid = NULL;
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+ m_vboundsChunkSize = 0;
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+ m_vboundsGridWidth = 0;
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+ m_vboundsGridLength = 0;
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// determine min/max axis-aligned bounding box (aabb) values
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switch (m_upAxis)
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@@ -108,6 +112,7 @@ void btHeightfieldTerrainShape::initialize(
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btHeightfieldTerrainShape::~btHeightfieldTerrainShape()
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{
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+ clearAccelerator();
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}
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void btHeightfieldTerrainShape::getAabb(const btTransform& t, btVector3& aabbMin, btVector3& aabbMax) const
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@@ -323,6 +328,8 @@ void btHeightfieldTerrainShape::processAllTriangles(btTriangleCallback* callback
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}
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}
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+ // TODO If m_vboundsGrid is available, use it to determine if we really need to process this area
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+
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for (int j = startJ; j < endJ; j++)
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{
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for (int x = startX; x < endX; x++)
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@@ -373,3 +380,416 @@ const btVector3& btHeightfieldTerrainShape::getLocalScaling() const
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{
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return m_localScaling;
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}
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+
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+
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+
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+struct GridRaycastState
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+{
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+ int x; // Next quad coords
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+ int z;
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+ int prev_x; // Previous quad coords
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+ int prev_z;
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+ btScalar param; // Exit param for previous quad
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+ btScalar prevParam; // Enter param for previous quad
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+ btScalar maxDistanceFlat;
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+ btScalar maxDistance3d;
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+};
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+
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+
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+// TODO Does it really need to take 3D vectors?
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+/// Iterates through a virtual 2D grid of unit-sized square cells,
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+/// and executes an action on each cell intersecting the given segment, ordered from begin to end.
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+/// Initially inspired by http://www.cse.yorku.ca/~amana/research/grid.pdf
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+template <typename Action_T>
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+void gridRaycast(Action_T &quadAction, const btVector3 &beginPos, const btVector3 &endPos)
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+{
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+ GridRaycastState rs;
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+ rs.maxDistance3d = beginPos.distance(endPos);
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+ if (rs.maxDistance3d < 0.0001)
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+ // Consider the ray is too small to hit anything
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+ return;
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+
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+ btScalar rayDirectionFlatX = endPos[0] - beginPos[0];
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+ btScalar rayDirectionFlatZ = endPos[2] - beginPos[2];
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+ rs.maxDistanceFlat = btSqrt(rayDirectionFlatX * rayDirectionFlatX + rayDirectionFlatZ * rayDirectionFlatZ);
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+
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+ if(rs.maxDistanceFlat < 0.0001)
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+ {
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+ // Consider the ray vertical
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+ rayDirectionFlatX = 0;
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+ rayDirectionFlatZ = 0;
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+ }
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+ else
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+ {
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+ rayDirectionFlatX /= rs.maxDistanceFlat;
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+ rayDirectionFlatZ /= rs.maxDistanceFlat;
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+ }
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+
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+ const int xiStep = rayDirectionFlatX > 0 ? 1 : rayDirectionFlatX < 0 ? -1 : 0;
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+ const int ziStep = rayDirectionFlatZ > 0 ? 1 : rayDirectionFlatZ < 0 ? -1 : 0;
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+
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+ const float infinite = 9999999;
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+ const btScalar paramDeltaX = xiStep != 0 ? 1.f / btFabs(rayDirectionFlatX) : infinite;
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+ const btScalar paramDeltaZ = ziStep != 0 ? 1.f / btFabs(rayDirectionFlatZ) : infinite;
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+
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+ // pos = param * dir
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+ btScalar paramCrossX; // At which value of `param` we will cross a x-axis lane?
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+ btScalar paramCrossZ; // At which value of `param` we will cross a z-axis lane?
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+
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+ // paramCrossX and paramCrossZ are initialized as being the first cross
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+ // X initialization
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+ if (xiStep != 0)
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+ {
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+ if (xiStep == 1)
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+ paramCrossX = (ceil(beginPos[0]) - beginPos[0]) * paramDeltaX;
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+ else
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+ paramCrossX = (beginPos[0] - floor(beginPos[0])) * paramDeltaX;
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+ }
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+ else
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+ paramCrossX = infinite; // Will never cross on X
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+
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+ // Z initialization
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+ if (ziStep != 0)
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+ {
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+ if (ziStep == 1)
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+ paramCrossZ = (ceil(beginPos[2]) - beginPos[2]) * paramDeltaZ;
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+ else
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+ paramCrossZ = (beginPos[2] - floor(beginPos[2])) * paramDeltaZ;
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+ }
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+ else
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+ paramCrossZ = infinite; // Will never cross on Z
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+
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+ rs.x = static_cast<int>(floor(beginPos[0]));
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+ rs.z = static_cast<int>(floor(beginPos[2]));
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+
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+ // Workaround cases where the ray starts at an integer position
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+ if (paramCrossX == 0.0)
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+ {
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+ paramCrossX += paramDeltaX;
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+ // If going backwards, we should ignore the position we would get by the above flooring,
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+ // because the ray is not heading in that direction
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+ if (xiStep == -1)
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+ rs.x -= 1;
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+ }
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+
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+ if (paramCrossZ == 0.0)
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+ {
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+ paramCrossZ += paramDeltaZ;
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+ if (ziStep == -1)
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+ rs.z -= 1;
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+ }
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+
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+ rs.prev_x = rs.x;
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+ rs.prev_z = rs.z;
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+ rs.param = 0;
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+
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+ while (true)
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+ {
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+ rs.prev_x = rs.x;
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+ rs.prev_z = rs.z;
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+ rs.prevParam = rs.param;
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+
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+ if (paramCrossX < paramCrossZ)
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+ {
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+ // X lane
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+ rs.x += xiStep;
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+ // Assign before advancing the param,
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+ // to be in sync with the initialization step
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+ rs.param = paramCrossX;
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+ paramCrossX += paramDeltaX;
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+ }
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+ else
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+ {
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+ // Z lane
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+ rs.z += ziStep;
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+ rs.param = paramCrossZ;
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+ paramCrossZ += paramDeltaZ;
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+ }
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+
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+ if (rs.param > rs.maxDistanceFlat)
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+ {
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+ rs.param = rs.maxDistanceFlat;
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+ quadAction(rs);
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+ break;
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+ }
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+ else
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+ quadAction(rs);
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+ }
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+}
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+
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+
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+struct ProcessTrianglesAction
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+{
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+ const btHeightfieldTerrainShape *shape;
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+ bool flipQuadEdges;
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+ bool useDiamondSubdivision;
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+ int width;
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+ int length;
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+ btTriangleCallback* callback;
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+
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+ void exec(int x, int z) const
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+ {
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+ if(x < 0 || z < 0 || x >= width || z >= length)
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+ return;
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+
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+ btVector3 vertices[3];
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+
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+ // Check quad
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+ if (flipQuadEdges || (useDiamondSubdivision && (((z + x) & 1) > 0)))
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+ {
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+ // First triangle
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+ shape->getVertex(x, z, vertices[0]);
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+ shape->getVertex(x + 1, z, vertices[1]);
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+ shape->getVertex(x + 1, z + 1, vertices[2]);
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+ callback->processTriangle(vertices, x, z);
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+
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+ // Second triangle
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+ shape->getVertex(x, z, vertices[0]);
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+ shape->getVertex(x + 1, z + 1, vertices[1]);
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+ shape->getVertex(x, z + 1, vertices[2]);
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+ callback->processTriangle(vertices, x, z);
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+ }
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+ else
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+ {
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+ // First triangle
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+ shape->getVertex(x, z, vertices[0]);
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+ shape->getVertex(x, z + 1, vertices[1]);
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+ shape->getVertex(x + 1, z, vertices[2]);
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+ callback->processTriangle(vertices, x, z);
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+
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+ // Second triangle
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+ shape->getVertex(x + 1, z, vertices[0]);
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+ shape->getVertex(x, z + 1, vertices[1]);
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+ shape->getVertex(x + 1, z + 1, vertices[2]);
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+ callback->processTriangle(vertices, x, z);
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+ }
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+ }
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+
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+ void operator ()(const GridRaycastState &bs) const
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+ {
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+ exec(bs.prev_x, bs.prev_z);
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+ }
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+};
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+
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+
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+struct ProcessVBoundsAction
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+{
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+ const btHeightfieldTerrainShape::Range *vbounds;
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+ int width;
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+ int length;
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+ int chunkSize;
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+
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+ btVector3 rayBegin;
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+ btVector3 rayEnd;
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+ btVector3 rayDir;
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+
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+ ProcessTrianglesAction processTriangles;
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+
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+ void operator ()(const GridRaycastState &rs) const
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+ {
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+ int x = rs.prev_x;
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+ int z = rs.prev_z;
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+
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+ if(x < 0 || z < 0 || x >= width || z >= length)
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+ return;
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+
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+ const btHeightfieldTerrainShape::Range chunk = vbounds[x + z * width];
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+
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+ btVector3 enterPos;
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+ btVector3 exitPos;
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+
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+ if (rs.maxDistanceFlat > 0.0001)
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+ {
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+ btScalar flatTo3d = chunkSize * rs.maxDistance3d / rs.maxDistanceFlat;
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+ btScalar enterParam3d = rs.prevParam * flatTo3d;
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+ btScalar exitParam3d = rs.param * flatTo3d;
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+ enterPos = rayBegin + rayDir * enterParam3d;
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+ exitPos = rayBegin + rayDir * exitParam3d;
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+
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+ // We did enter the flat projection of the AABB,
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+ // but we have to check if we intersect it on the vertical axis
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+ if (enterPos[1] > chunk.max && exitPos[1] > chunk.max)
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+ return;
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+ if (enterPos[1] < chunk.min && exitPos[1] < chunk.min)
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+ return;
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+ }
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+ else
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+ {
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+ // Consider the ray vertical
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+ // (though we shouldn't reach this often because there is an early check up-front)
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+ enterPos = rayBegin;
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+ exitPos = rayEnd;
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+ }
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+
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+ gridRaycast(processTriangles, enterPos, exitPos);
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+ // Note: it could be possible to have more than one grid at different levels,
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+ // to do this there would be a branch using a pointer to another ProcessVBoundsAction
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+ }
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+};
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+
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+
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+// TODO How do I interrupt the ray when there is a hit? `callback` does not return any result
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+/// Performs a raycast using a hierarchical Bresenham algorithm.
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+/// Does not allocate any memory by itself.
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+void btHeightfieldTerrainShape::performRaycast(btTriangleCallback* callback, const btVector3& raySource, const btVector3& rayTarget) const
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+{
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+ // Transform to cell-local
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+ btVector3 beginPos = raySource / m_localScaling;
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+ btVector3 endPos = rayTarget / m_localScaling;
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+ beginPos += m_localOrigin;
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+ endPos += m_localOrigin;
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+
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+ ProcessTrianglesAction processTriangles;
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+ processTriangles.shape = this;
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+ processTriangles.flipQuadEdges = m_flipQuadEdges;
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+ processTriangles.useDiamondSubdivision = m_useDiamondSubdivision;
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+ processTriangles.callback = callback;
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+ processTriangles.width = m_heightStickWidth - 1;
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+ processTriangles.length = m_heightStickLength - 1;
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+
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+ // TODO Transform vectors to account for m_upAxis
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+ int iBeginX = static_cast<int>(floor(beginPos[0]));
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+ int iBeginZ = static_cast<int>(floor(beginPos[2]));
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+ int iEndX = static_cast<int>(floor(endPos[0]));
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+ int iEndZ = static_cast<int>(floor(endPos[2]));
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+
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+ if (iBeginX == iEndX && iBeginZ == iEndZ)
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+ {
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+ // The ray will never cross quads within the plane,
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+ // so directly process triangles within one quad
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+ // (typically, vertical rays should end up here)
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+ processTriangles.exec(iBeginX, iEndZ);
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+ return;
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+ }
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+
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+ if (m_vboundsGrid == NULL)
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+ {
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+ // Process all quads intersecting the flat projection of the ray
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+ gridRaycast(processTriangles, beginPos, endPos);
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+ }
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+ else
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+ {
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+ btVector3 rayDiff = endPos - beginPos;
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+ btScalar flatDistance2 = rayDiff[0] * rayDiff[0] + rayDiff[2] * rayDiff[2];
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+ if (flatDistance2 < m_vboundsChunkSize * m_vboundsChunkSize)
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+ {
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+ // Don't use chunks, the ray is too short in the plane
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+ gridRaycast(processTriangles, beginPos, endPos);
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+ }
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+
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+ ProcessVBoundsAction processVBounds;
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+ processVBounds.width = m_vboundsGridWidth;
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+ processVBounds.length = m_vboundsGridLength;
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+ processVBounds.vbounds = m_vboundsGrid;
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+ processVBounds.rayBegin = beginPos;
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+ processVBounds.rayEnd = endPos;
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+ processVBounds.rayDir = rayDiff.normalized();
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+ processVBounds.processTriangles = processTriangles;
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+ processVBounds.chunkSize = m_vboundsChunkSize;
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+ // The ray is long, run raycast on a higher-level grid
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+ gridRaycast(processVBounds, beginPos / m_vboundsChunkSize, endPos / m_vboundsChunkSize);
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+ }
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+}
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+
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+
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+/// Builds a grid data structure storing the min and max heights of the terrain in chunks.
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+/// if chunkSize is zero, that accelerator is removed.
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+/// If you modify the heights, you need to rebuild this accelerator.
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+void btHeightfieldTerrainShape::buildAccelerator(int chunkSize)
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+{
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+ if (chunkSize <= 0)
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+ {
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+ clearAccelerator();
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+ return;
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+ }
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+
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+ m_vboundsChunkSize = chunkSize;
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+ int nChunksX = m_heightStickWidth / chunkSize;
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+ int nChunksZ = m_heightStickLength / chunkSize;
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+
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+ if (m_heightStickWidth % chunkSize > 0)
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+ ++nChunksX; // In case terrain size isn't dividable by chunk size
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+ if (m_heightStickLength % chunkSize > 0)
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+ ++nChunksZ;
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+
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+ if(m_vboundsGridWidth != nChunksX || m_vboundsGridLength != nChunksZ)
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+ {
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+ clearAccelerator();
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+ m_vboundsGridWidth = nChunksX;
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+ m_vboundsGridLength = nChunksZ;
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+ }
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+
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+ if (nChunksX == 0 || nChunksZ == 0)
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+ return;
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+
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+ // TODO What is the recommended way to allocate this?
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+ // This data structure is only reallocated if the required size changed
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+ if (m_vboundsGrid == NULL)
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+ m_vboundsGrid = new Range[nChunksX * nChunksZ];
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+
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+ // Compute min and max height for all chunks
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+ for (int cz = 0; cz < nChunksZ; ++cz)
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+ {
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+ int z0 = cz * chunkSize;
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+
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+ for (int cx = 0; cx < nChunksX; ++cx)
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+ {
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+ int x0 = cx * chunkSize;
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+
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+ Range r;
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+
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+ r.min = getRawHeightFieldValue(x0, z0);
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+ r.max = r.min;
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+
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+ // Compute min and max height for this chunk.
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+ // We have to include one extra cell to account for neighbors.
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+ // Here is why:
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+ // Say we have a flat terrain, and a plateau that fits a chunk perfectly.
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+ //
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+ // Left Right
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+ // 0---0---0---1---1---1
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+ // | | | | | |
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+ // 0---0---0---1---1---1
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+ // | | | | | |
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+ // 0---0---0---1---1---1
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+ // x
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+ //
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+ // If the AABB for the Left chunk did not share vertices with the Right,
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+ // then we would fail collision tests at x due to a gap.
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|
|
+ //
|
|
|
+ for (int z = z0; z < z0 + chunkSize + 1; ++z)
|
|
|
+ {
|
|
|
+ if (z >= m_heightStickLength)
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|
|
+ continue;
|
|
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+
|
|
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+ for (int x = x0; x < x0 + chunkSize + 1; ++x)
|
|
|
+ {
|
|
|
+ if (x >= m_heightStickWidth)
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|
|
+ continue;
|
|
|
+
|
|
|
+ btScalar height = getRawHeightFieldValue(x, z);
|
|
|
+
|
|
|
+ if (height < r.min)
|
|
|
+ r.min = height;
|
|
|
+ else if (height > r.max)
|
|
|
+ r.max = height;
|
|
|
+ }
|
|
|
+ }
|
|
|
+
|
|
|
+ m_vboundsGrid[cx + cz * nChunksX] = r;
|
|
|
+ }
|
|
|
+ }
|
|
|
+}
|
|
|
+
|
|
|
+
|
|
|
+void btHeightfieldTerrainShape::clearAccelerator()
|
|
|
+{
|
|
|
+ if (m_vboundsGrid)
|
|
|
+ {
|
|
|
+ // TODO What is the recommended way to deallocate this?
|
|
|
+ delete[] m_vboundsGrid;
|
|
|
+ m_vboundsGrid = 0;
|
|
|
+ }
|
|
|
+}
|
|
|
+
|
|
|
+
|
Marc Gilleron