Revision control
++ // Copyright 2009-2021 Intel Corporation
++ // SPDX-License-Identifier: Apache-2.0
++
++ #include "bvh_rotate.h"
++
++ namespace embree
++ {
++ namespace isa
++ {
++ /*! Computes half surface area of box. */
++ __forceinline float halfArea3f(const BBox<vfloat4>& box) {
++ const vfloat4 d = box.size();
++ const vfloat4 a = d*shuffle<1,2,0,3>(d);
++ return a[0]+a[1]+a[2];
++ }
++
++ size_t BVHNRotate<4>::rotate(NodeRef parentRef, size_t depth)
++ {
++ /*! nothing to rotate if we reached a leaf node. */
++ if (parentRef.isBarrier()) return 0;
++ if (parentRef.isLeaf()) return 0;
++ AABBNode* parent = parentRef.getAABBNode();
++
++ /*! rotate all children first */
++ vint4 cdepth;
++ for (size_t c=0; c<4; c++)
++ cdepth[c] = (int)rotate(parent->child(c),depth+1);
++
++ /* compute current areas of all children */
++ vfloat4 sizeX = parent->upper_x-parent->lower_x;
++ vfloat4 sizeY = parent->upper_y-parent->lower_y;
++ vfloat4 sizeZ = parent->upper_z-parent->lower_z;
++ vfloat4 childArea = madd(sizeX,(sizeY + sizeZ),sizeY*sizeZ);
++
++ /*! get node bounds */
++ BBox<vfloat4> child1_0,child1_1,child1_2,child1_3;
++ parent->bounds(child1_0,child1_1,child1_2,child1_3);
++
++ /*! Find best rotation. We pick a first child (child1) and a sub-child
++ (child2child) of a different second child (child2), and swap child1
++ and child2child. We perform the best such swap. */
++ float bestArea = 0;
++ size_t bestChild1 = -1, bestChild2 = -1, bestChild2Child = -1;
++ for (size_t c2=0; c2<4; c2++)
++ {
++ /*! ignore leaf nodes as we cannot descent into them */
++ if (parent->child(c2).isBarrier()) continue;
++ if (parent->child(c2).isLeaf()) continue;
++ AABBNode* child2 = parent->child(c2).getAABBNode();
++
++ /*! transpose child bounds */
++ BBox<vfloat4> child2c0,child2c1,child2c2,child2c3;
++ child2->bounds(child2c0,child2c1,child2c2,child2c3);
++
++ /*! put child1_0 at each child2 position */
++ float cost00 = halfArea3f(merge(child1_0,child2c1,child2c2,child2c3));
++ float cost01 = halfArea3f(merge(child2c0,child1_0,child2c2,child2c3));
++ float cost02 = halfArea3f(merge(child2c0,child2c1,child1_0,child2c3));
++ float cost03 = halfArea3f(merge(child2c0,child2c1,child2c2,child1_0));
++ vfloat4 cost0 = vfloat4(cost00,cost01,cost02,cost03);
++ vfloat4 min0 = vreduce_min(cost0);
++ int pos0 = (int)bsf(movemask(min0 == cost0));
++
++ /*! put child1_1 at each child2 position */
++ float cost10 = halfArea3f(merge(child1_1,child2c1,child2c2,child2c3));
++ float cost11 = halfArea3f(merge(child2c0,child1_1,child2c2,child2c3));
++ float cost12 = halfArea3f(merge(child2c0,child2c1,child1_1,child2c3));
++ float cost13 = halfArea3f(merge(child2c0,child2c1,child2c2,child1_1));
++ vfloat4 cost1 = vfloat4(cost10,cost11,cost12,cost13);
++ vfloat4 min1 = vreduce_min(cost1);
++ int pos1 = (int)bsf(movemask(min1 == cost1));
++
++ /*! put child1_2 at each child2 position */
++ float cost20 = halfArea3f(merge(child1_2,child2c1,child2c2,child2c3));
++ float cost21 = halfArea3f(merge(child2c0,child1_2,child2c2,child2c3));
++ float cost22 = halfArea3f(merge(child2c0,child2c1,child1_2,child2c3));
++ float cost23 = halfArea3f(merge(child2c0,child2c1,child2c2,child1_2));
++ vfloat4 cost2 = vfloat4(cost20,cost21,cost22,cost23);
++ vfloat4 min2 = vreduce_min(cost2);
++ int pos2 = (int)bsf(movemask(min2 == cost2));
++
++ /*! put child1_3 at each child2 position */
++ float cost30 = halfArea3f(merge(child1_3,child2c1,child2c2,child2c3));
++ float cost31 = halfArea3f(merge(child2c0,child1_3,child2c2,child2c3));
++ float cost32 = halfArea3f(merge(child2c0,child2c1,child1_3,child2c3));
++ float cost33 = halfArea3f(merge(child2c0,child2c1,child2c2,child1_3));
++ vfloat4 cost3 = vfloat4(cost30,cost31,cost32,cost33);
++ vfloat4 min3 = vreduce_min(cost3);
++ int pos3 = (int)bsf(movemask(min3 == cost3));
++
++ /*! find best other child */
++ vfloat4 area0123 = vfloat4(extract<0>(min0),extract<0>(min1),extract<0>(min2),extract<0>(min3)) - vfloat4(childArea[c2]);
++ int pos[4] = { pos0,pos1,pos2,pos3 };
++ const size_t mbd = BVH4::maxBuildDepth;
++ vbool4 valid = vint4(int(depth+1))+cdepth <= vint4(mbd); // only select swaps that fulfill depth constraints
++ valid &= vint4(int(c2)) != vint4(step);
++ if (none(valid)) continue;
++ size_t c1 = select_min(valid,area0123);
++ float area = area0123[c1];
++ if (c1 == c2) continue; // can happen if bounds are NANs
++
++ /*! accept a swap when it reduces cost and is not swapping a node with itself */
++ if (area < bestArea) {
++ bestArea = area;
++ bestChild1 = c1;
++ bestChild2 = c2;
++ bestChild2Child = pos[c1];
++ }
++ }
++
++ /*! if we did not find a swap that improves the SAH then do nothing */
++ if (bestChild1 == size_t(-1)) return 1+reduce_max(cdepth);
++
++ /*! perform the best found tree rotation */
++ AABBNode* child2 = parent->child(bestChild2).getAABBNode();
++ AABBNode::swap(parent,bestChild1,child2,bestChild2Child);
++ parent->setBounds(bestChild2,child2->bounds());
++ AABBNode::compact(parent);
++ AABBNode::compact(child2);
++
++ /*! This returned depth is conservative as the child that was
++ * pulled up in the tree could have been on the critical path. */
++ cdepth[bestChild1]++; // bestChild1 was pushed down one level
++ return 1+reduce_max(cdepth);
++ }
++ }
++ }