bullet3/examples/ExampleBrowser/CollisionShape2TriangleMesh.cpp

#include "CollisionShape2TriangleMesh.h"

#include "btBulletCollisionCommon.h"
#include "BulletCollision/CollisionShapes/btShapeHull.h"  //to create a tesselation of a generic btConvexShape
#include "BulletCollision/CollisionShapes/btConvexPolyhedron.h"

void CollisionShape2TriangleMesh(btCollisionShape* collisionShape, const btTransform& parentTransform, btAlignedObjectArray<btVector3>& vertexPositions, btAlignedObjectArray<btVector3>& vertexNormals, btAlignedObjectArray<int>& indicesOut)

{
	//todo: support all collision shape types
	switch (collisionShape->getShapeType())
	{
		case SOFTBODY_SHAPE_PROXYTYPE:
		{
			//skip the soft body collision shape for now
			break;
		}
		case STATIC_PLANE_PROXYTYPE:
		{
			//draw a box, oriented along the plane normal
			const btStaticPlaneShape* staticPlaneShape = static_cast<const btStaticPlaneShape*>(collisionShape);
			btScalar planeConst = staticPlaneShape->getPlaneConstant();
			const btVector3& planeNormal = staticPlaneShape->getPlaneNormal();
			btVector3 planeOrigin = planeNormal * planeConst;
			btVector3 vec0, vec1;
			btPlaneSpace1(planeNormal, vec0, vec1);
			btScalar vecLen = 100.f;
			btVector3 verts[4];

			verts[0] = planeOrigin + vec0 * vecLen + vec1 * vecLen;
			verts[1] = planeOrigin - vec0 * vecLen + vec1 * vecLen;
			verts[2] = planeOrigin - vec0 * vecLen - vec1 * vecLen;
			verts[3] = planeOrigin + vec0 * vecLen - vec1 * vecLen;

			int startIndex = vertexPositions.size();
			indicesOut.push_back(startIndex + 0);
			indicesOut.push_back(startIndex + 1);
			indicesOut.push_back(startIndex + 2);
			indicesOut.push_back(startIndex + 0);
			indicesOut.push_back(startIndex + 2);
			indicesOut.push_back(startIndex + 3);

			btVector3 triNormal = parentTransform.getBasis() * planeNormal;

			for (int i = 0; i < 4; i++)
			{
				btVector3 vtxPos;
				btVector3 pos = parentTransform * verts[i];
				vertexPositions.push_back(pos);
				vertexNormals.push_back(triNormal);
			}
			break;
		}
		case TRIANGLE_MESH_SHAPE_PROXYTYPE:
		{
			btBvhTriangleMeshShape* trimesh = (btBvhTriangleMeshShape*)collisionShape;
			btVector3 trimeshScaling = trimesh->getLocalScaling();
			btStridingMeshInterface* meshInterface = trimesh->getMeshInterface();
			btAlignedObjectArray<btVector3> vertices;
			btAlignedObjectArray<int> indices;

			for (int partId = 0; partId < meshInterface->getNumSubParts(); partId++)
			{
				const unsigned char* vertexbase = 0;
				int numverts = 0;
				PHY_ScalarType type = PHY_INTEGER;
				int stride = 0;
				const unsigned char* indexbase = 0;
				int indexstride = 0;
				int numfaces = 0;
				PHY_ScalarType indicestype = PHY_INTEGER;
				//PHY_ScalarType indexType=0;

				btVector3 triangleVerts[3];
				meshInterface->getLockedReadOnlyVertexIndexBase(&vertexbase, numverts, type, stride, &indexbase, indexstride, numfaces, indicestype, partId);
				btVector3 aabbMin, aabbMax;

				for (int triangleIndex = 0; triangleIndex < numfaces; triangleIndex++)
				{
					unsigned int* gfxbase = (unsigned int*)(indexbase + triangleIndex * indexstride);

					for (int j = 2; j >= 0; j--)
					{
						int graphicsindex = indicestype == PHY_SHORT ? ((unsigned short*)gfxbase)[j] : gfxbase[j];
						if (type == PHY_FLOAT)
						{
							float* graphicsbase = (float*)(vertexbase + graphicsindex * stride);
							triangleVerts[j] = btVector3(
								graphicsbase[0] * trimeshScaling.getX(),
								graphicsbase[1] * trimeshScaling.getY(),
								graphicsbase[2] * trimeshScaling.getZ());
						}
						else
						{
							double* graphicsbase = (double*)(vertexbase + graphicsindex * stride);
							triangleVerts[j] = btVector3(btScalar(graphicsbase[0] * trimeshScaling.getX()),
														 btScalar(graphicsbase[1] * trimeshScaling.getY()),
														 btScalar(graphicsbase[2] * trimeshScaling.getZ()));
						}
					}
					indices.push_back(vertices.size());
					vertices.push_back(triangleVerts[0]);
					indices.push_back(vertices.size());
					vertices.push_back(triangleVerts[1]);
					indices.push_back(vertices.size());
					vertices.push_back(triangleVerts[2]);

					btVector3 triNormal = (triangleVerts[1] - triangleVerts[0]).cross(triangleVerts[2] - triangleVerts[0]);
					btScalar dot = triNormal.dot(triNormal);

					//cull degenerate triangles
					if (dot >= SIMD_EPSILON * SIMD_EPSILON)
					{
						triNormal /= btSqrt(dot);
						for (int v = 0; v < 3; v++)
						{
							btVector3 pos = parentTransform * triangleVerts[v];
							indicesOut.push_back(vertexPositions.size());
							vertexPositions.push_back(pos);
							vertexNormals.push_back(triNormal);
						}
					}
				}
			}

			break;
		}
		default:
		{
			if (collisionShape->isConvex())
			{
				btConvexShape* convex = (btConvexShape*)collisionShape;
				{
					const btConvexPolyhedron* pol = 0;
					if (convex->isPolyhedral())
					{
						btPolyhedralConvexShape* poly = (btPolyhedralConvexShape*)convex;
						pol = poly->getConvexPolyhedron();
					}

					if (pol)
					{
						for (int v = 0; v < pol->m_vertices.size(); v++)
						{
							vertexPositions.push_back(pol->m_vertices[v]);
							btVector3 norm = pol->m_vertices[v];
							norm.safeNormalize();
							vertexNormals.push_back(norm);
						}
						for (int f = 0; f < pol->m_faces.size(); f++)
						{
							for (int ii = 2; ii < pol->m_faces[f].m_indices.size(); ii++)
							{
								indicesOut.push_back(pol->m_faces[f].m_indices[0]);
								indicesOut.push_back(pol->m_faces[f].m_indices[ii - 1]);
								indicesOut.push_back(pol->m_faces[f].m_indices[ii]);
							}
						}
					}
					else
					{
						btShapeHull* hull = new btShapeHull(convex);
						hull->buildHull(0.0, 1);

						{
							//int strideInBytes = 9*sizeof(float);
							//int numVertices = hull->numVertices();
							//int numIndices =hull->numIndices();

							for (int t = 0; t < hull->numTriangles(); t++)
							{
								btVector3 triNormal;

								int index0 = hull->getIndexPointer()[t * 3 + 0];
								int index1 = hull->getIndexPointer()[t * 3 + 1];
								int index2 = hull->getIndexPointer()[t * 3 + 2];
								btVector3 pos0 = parentTransform * hull->getVertexPointer()[index0];
								btVector3 pos1 = parentTransform * hull->getVertexPointer()[index1];
								btVector3 pos2 = parentTransform * hull->getVertexPointer()[index2];
								triNormal = (pos1 - pos0).cross(pos2 - pos0);
								triNormal.safeNormalize();

								for (int v = 0; v < 3; v++)
								{
									int index = hull->getIndexPointer()[t * 3 + v];
									btVector3 pos = parentTransform * hull->getVertexPointer()[index];
									indicesOut.push_back(vertexPositions.size());
									vertexPositions.push_back(pos);
									vertexNormals.push_back(triNormal);
								}
							}
						}
						delete hull;
					}
				}
			}
			else
			{
				if (collisionShape->isCompound())
				{
					btCompoundShape* compound = (btCompoundShape*)collisionShape;
					for (int i = 0; i < compound->getNumChildShapes(); i++)
					{
						btTransform childWorldTrans = parentTransform * compound->getChildTransform(i);
						CollisionShape2TriangleMesh(compound->getChildShape(i), childWorldTrans, vertexPositions, vertexNormals, indicesOut);
					}
				}
				else
				{
					if (collisionShape->getShapeType() == SDF_SHAPE_PROXYTYPE)
					{
						//not yet
					}
					else
					{
						btAssert(0);
					}
				}
			}
		}
	};
}