Physx之解決三角形頂點相近卡住的問題
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今天遇到一個問題,角色卡在一個模型邊上,在PVD看模型也比較正常,一直調試跟蹤,最終找到了問題所在。
原因
1.問題出在最後一個sweepCapsuleTriangles函數里面,代碼如下:
#ifdef __SPU__ Vec3V dummy1, dummy2; FloatV result = distanceSegmentTriangleSquared( V3LoadU(capsule.p0), V3LoadU(capsule.p1), V3LoadU(p0), V3LoadU(p1), V3LoadU(p2), dummy1, dummy2); PxReal dist2 = FStore(result); #else // AP: switching to SIMD version produced -25% regression in Sweep*SphereHfld PxReal dist2 = distanceSegmentTriangleSquared(capsule.p0, segmentExtent, p0, p1 - p0, p2 - p0); #endif if (dist2<=r2) { hitIndex = i; t = 0.0f; normal = -unitDir; outFlags = PxHitFlag::eDISTANCE|PxHitFlag::eNORMAL; _triNormal = denormalizedNormal.getNormalized(); return true; }
當p0、p1和p2有有兩個點相同的時候,會導致p1-p0和p2-p0其中一個向量爲0,得到的dist2爲負無窮大,所以就會執行代碼中的條件語句。最終結果是move函數移動成功了,但是隻移動了0的位移,表現上就是一直卡在那個地方。
- 至於頂點一樣的情況,其實並不是完全一樣,而是有很小的差異。再加上浮點數運算會丟失精度,這個很小的差異被抹掉了,所以到上面代碼的時候就出現相同的點了。
計算的代碼位置(沒看太明白):
PX_FORCE_INLINE void Gu::TriangleMesh::computeWorldTriangle(PxTriangle& worldTri, PxTriangleID triangleIndex, const Cm::Matrix34& worldMatrix, PxU32* PX_RESTRICT vertexIndices, PxU32* PX_RESTRICT adjacencyIndices) const { PxU32 vref0, vref1, vref2; if(mMesh.has16BitIndices()) { const Gu::TriangleT<PxU16>& T = ((const Gu::TriangleT<PxU16>*)getTrianglesFast())[triangleIndex]; vref0 = T.v[0]; vref1 = T.v[1]; vref2 = T.v[2]; } else { const Gu::TriangleT<PxU32>& T = ((const Gu::TriangleT<PxU32>*)getTrianglesFast())[triangleIndex]; vref0 = T.v[0]; vref1 = T.v[1]; vref2 = T.v[2]; } const PxVec3* PX_RESTRICT vertices = getVerticesFast(); worldTri.verts[0] = worldMatrix.transform(vertices[vref0]); worldTri.verts[1] = worldMatrix.transform(vertices[vref1]); worldTri.verts[2] = worldMatrix.transform(vertices[vref2]); if(vertexIndices) { vertexIndices[0] = vref0; vertexIndices[1] = vref1; vertexIndices[2] = vref2; } if(adjacencyIndices) { if(mMesh.getAdjacencies()) { adjacencyIndices[0] = mMesh.getAdjacencies()[triangleIndex*3 + 0]; adjacencyIndices[1] = mMesh.getAdjacencies()[triangleIndex*3 + 1]; adjacencyIndices[2] = mMesh.getAdjacencies()[triangleIndex*3 + 2]; } else { adjacencyIndices[0] = 0xffffffff; adjacencyIndices[1] = 0xffffffff; adjacencyIndices[2] = 0xffffffff; } } }
- 問題數據
出現問題的時候,斷點的數據如下:
vertices[vref0] = {x = -4.10000086, y = -0.200000167, z = -3.56512594} vertices[vref1] = {x = -4.10000086, y = -0.200000077, z = -3.56512594} vertices[vref2] = {x = -4.10000086, y = -0.200000212, z = -4.10000229} worldMatrix.transform.base3 = {x=72.3379974 y=4.76143503 z=18.5843773 } // 得到這個三角形前兩個點完全一樣 worldTri.verts[0] = { x = 68.237990, y = 4.56143475, z = 15.0192509} worldTri.verts[1] = { x = 68.237990, y = 4.56143475, z = 15.0192509} worldTri.verts[2] = { x = 68.237990, y = 4.56143475, z = 14.4843750}
簡單來說就是:
4.76143503 + -0.200000167 = 4.56143475 4.76143503 + -0.200000077 = 4.56143475
至於爲什麼請參考另外一篇文章[1] 爲什單精度浮點數的有效位時7位
解決
-
1.把頂點傳到PhysX之前,先檢查一遍。可以刪掉重新組織Vertex和Index,我簡單處理的方法是把兩個頂點很近的時候,標記爲同一個索引,這樣的三角形比較容易標識
if (fMinDist <= 1e-5) { // set the same index, and then cooking will process it. eREMOVE_DUPLICATED_TRIANGLES pIndices[3 * i + nIndexIndex1] = pIndices[3 * i + nIndexIndex2]; }
- 2.PhysxCooking的參數增加去重的Flag,這樣上面的三角形就會被PhysX剔除,從而就解決了這樣的問題:如下
physx::PxCookingParams cookingParams(scale); cookingParams.buildTriangleAdjacencies = true; cookingParams.meshPreprocessParams = PxMeshPreprocessingFlags(PxMeshPreprocessingFlag::eWELD_VERTICES | PxMeshPreprocessingFlag::eREMOVE_UNREFERENCED_VERTICES | PxMeshPreprocessingFlag::eREMOVE_DUPLICATED_TRIANGLES);
參考
[1] 爲什麼單精度浮點數的精度是7位