binning.cpp

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/* SPDX-FileCopyrightText: 2009-2011 Intel Corporation
 * SPDX-FileCopyrightText: 2012-2022 Blender Foundation
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Adapted code from Intel Corporation. */
 
// #define __KERNEL_SSE__
 
#include "bvh/binning.h"
 
#include <stdlib.h>
 
#include "util/algorithm.h"
#include "util/boundbox.h"
#include "util/types.h"
 
CCL_NAMESPACE_BEGIN
 
/* SSE replacements */
 
__forceinline void prefetch_L1(const void * /*ptr*/) {}
__forceinline void prefetch_L2(const void * /*ptr*/) {}
__forceinline void prefetch_L3(const void * /*ptr*/) {}
__forceinline void prefetch_NTA(const void * /*ptr*/) {}
 
template<size_t src> __forceinline float extract(const int4 &b)
{
  return b[src];
}
template<size_t dst> __forceinline const float4 insert(const float4 &a, const float b)
{
  float4 r = a;
  r[dst] = b;
  return r;
}
 
__forceinline int get_best_dimension(const float4 &bestSAH)
{
  // return (int)__bsf(movemask(reduce_min(bestSAH) == bestSAH));
 
  float minSAH = min(bestSAH.x, min(bestSAH.y, bestSAH.z));
 
  if (bestSAH.x == minSAH) {
    return 0;
  }
  else if (bestSAH.y == minSAH) {
    return 1;
  }
  else {
    return 2;
  }
}
 
/* BVH Object Binning */
 
BVHObjectBinning::BVHObjectBinning(const BVHRange &job,
                                   BVHReference *prims,
                                   const BVHUnaligned *unaligned_heuristic,
                                   const Transform *aligned_space)
    : BVHRange(job),
      splitSAH(FLT_MAX),
      dim(0),
      pos(0),
      unaligned_heuristic_(unaligned_heuristic),
      aligned_space_(aligned_space)
{
  if (aligned_space_ == NULL) {
    bounds_ = bounds();
    cent_bounds_ = cent_bounds();
  }
  else {
    /* TODO(sergey): With some additional storage we can avoid
     * need in re-calculating this.
     */
    bounds_ = unaligned_heuristic->compute_aligned_boundbox(
        *this, prims, *aligned_space, &cent_bounds_);
  }
 
  /* compute number of bins to use and precompute scaling factor for binning */
  num_bins = min(size_t(MAX_BINS), size_t(4.0f + 0.05f * size()));
  scale = rcp(cent_bounds_.size()) * make_float3((float)num_bins);
 
  /* initialize binning counter and bounds */
  BoundBox bin_bounds[MAX_BINS][4]; /* bounds for every bin in every dimension */
  int4 bin_count[MAX_BINS];         /* number of primitives mapped to bin */
 
  for (size_t i = 0; i < num_bins; i++) {
    bin_count[i] = make_int4(0);
    bin_bounds[i][0] = bin_bounds[i][1] = bin_bounds[i][2] = BoundBox::empty;
  }
 
  /* map geometry to bins, unrolled once */
  {
    int64_t i;
 
    for (i = 0; i < int64_t(size()) - 1; i += 2) {
      prefetch_L2(&prims[start() + i + 8]);
 
      /* map even and odd primitive to bin */
      const BVHReference &prim0 = prims[start() + i + 0];
      const BVHReference &prim1 = prims[start() + i + 1];
 
      BoundBox bounds0 = get_prim_bounds(prim0);
      BoundBox bounds1 = get_prim_bounds(prim1);
 
      int4 bin0 = get_bin(bounds0);
      int4 bin1 = get_bin(bounds1);
 
      /* increase bounds for bins for even primitive */
      int b00 = (int)extract<0>(bin0);
      bin_count[b00][0]++;
      bin_bounds[b00][0].grow(bounds0);
      int b01 = (int)extract<1>(bin0);
      bin_count[b01][1]++;
      bin_bounds[b01][1].grow(bounds0);
      int b02 = (int)extract<2>(bin0);
      bin_count[b02][2]++;
      bin_bounds[b02][2].grow(bounds0);
 
      /* increase bounds of bins for odd primitive */
      int b10 = (int)extract<0>(bin1);
      bin_count[b10][0]++;
      bin_bounds[b10][0].grow(bounds1);
      int b11 = (int)extract<1>(bin1);
      bin_count[b11][1]++;
      bin_bounds[b11][1].grow(bounds1);
      int b12 = (int)extract<2>(bin1);
      bin_count[b12][2]++;
      bin_bounds[b12][2].grow(bounds1);
    }
 
    /* for uneven number of primitives */
    if (i < int64_t(size())) {
      /* map primitive to bin */
      const BVHReference &prim0 = prims[start() + i];
      BoundBox bounds0 = get_prim_bounds(prim0);
      int4 bin0 = get_bin(bounds0);
 
      /* increase bounds of bins */
      int b00 = (int)extract<0>(bin0);
      bin_count[b00][0]++;
      bin_bounds[b00][0].grow(bounds0);
      int b01 = (int)extract<1>(bin0);
      bin_count[b01][1]++;
      bin_bounds[b01][1].grow(bounds0);
      int b02 = (int)extract<2>(bin0);
      bin_count[b02][2]++;
      bin_bounds[b02][2].grow(bounds0);
    }
  }
 
  /* sweep from right to left and compute parallel prefix of merged bounds */
  float4 r_area[MAX_BINS];  /* area of bounds of primitives on the right */
  float4 r_count[MAX_BINS]; /* number of primitives on the right */
  int4 count = make_int4(0);
 
  BoundBox bx = BoundBox::empty;
  BoundBox by = BoundBox::empty;
  BoundBox bz = BoundBox::empty;
 
  for (size_t i = num_bins - 1; i > 0; i--) {
    count = count + bin_count[i];
    r_count[i] = blocks(count);
 
    bx = merge(bx, bin_bounds[i][0]);
    r_area[i][0] = bx.half_area();
    by = merge(by, bin_bounds[i][1]);
    r_area[i][1] = by.half_area();
    bz = merge(bz, bin_bounds[i][2]);
    r_area[i][2] = bz.half_area();
    r_area[i][3] = r_area[i][2];
  }
 
  /* sweep from left to right and compute SAH */
  int4 ii = make_int4(1);
  float4 bestSAH = make_float4(FLT_MAX);
  int4 bestSplit = make_int4(-1);
 
  count = make_int4(0);
 
  bx = BoundBox::empty;
  by = BoundBox::empty;
  bz = BoundBox::empty;
 
  for (size_t i = 1; i < num_bins; i++, ii += make_int4(1)) {
    count = count + bin_count[i - 1];
 
    bx = merge(bx, bin_bounds[i - 1][0]);
    float Ax = bx.half_area();
    by = merge(by, bin_bounds[i - 1][1]);
    float Ay = by.half_area();
    bz = merge(bz, bin_bounds[i - 1][2]);
    float Az = bz.half_area();
 
    float4 lCount = blocks(count);
    float4 lArea = make_float4(Ax, Ay, Az, Az);
    float4 sah = lArea * lCount + r_area[i] * r_count[i];
 
    bestSplit = select(sah < bestSAH, ii, bestSplit);
    bestSAH = min(sah, bestSAH);
  }
 
  int4 mask = float3_to_float4(cent_bounds_.size()) <= zero_float4();
  bestSAH = insert<3>(select(mask, make_float4(FLT_MAX), bestSAH), FLT_MAX);
 
  /* find best dimension */
  dim = get_best_dimension(bestSAH);
  splitSAH = bestSAH[dim];
  pos = bestSplit[dim];
  leafSAH = bounds_.half_area() * blocks(size());
}
 
void BVHObjectBinning::split(BVHReference *prims,
                             BVHObjectBinning &left_o,
                             BVHObjectBinning &right_o) const
{
  size_t N = size();
 
  BoundBox lgeom_bounds = BoundBox::empty;
  BoundBox rgeom_bounds = BoundBox::empty;
  BoundBox lcent_bounds = BoundBox::empty;
  BoundBox rcent_bounds = BoundBox::empty;
 
  int64_t l = 0, r = N - 1;
 
  while (l <= r) {
    prefetch_L2(&prims[start() + l + 8]);
    prefetch_L2(&prims[start() + r - 8]);
 
    BVHReference prim = prims[start() + l];
    BoundBox unaligned_bounds = get_prim_bounds(prim);
    float3 unaligned_center = unaligned_bounds.center2();
    float3 center = prim.bounds().center2();
 
    if (get_bin(unaligned_center)[dim] < pos) {
      lgeom_bounds.grow(prim.bounds());
      lcent_bounds.grow(center);
      l++;
    }
    else {
      rgeom_bounds.grow(prim.bounds());
      rcent_bounds.grow(center);
      swap(prims[start() + l], prims[start() + r]);
      r--;
    }
  }
  /* finish */
  if (l != 0 && N - 1 - r != 0) {
    right_o = BVHObjectBinning(BVHRange(rgeom_bounds, rcent_bounds, start() + l, N - 1 - r),
                               prims);
    left_o = BVHObjectBinning(BVHRange(lgeom_bounds, lcent_bounds, start(), l), prims);
    return;
  }
 
  /* object medium split if we did not make progress, can happen when all
   * primitives have same centroid */
  lgeom_bounds = BoundBox::empty;
  rgeom_bounds = BoundBox::empty;
  lcent_bounds = BoundBox::empty;
  rcent_bounds = BoundBox::empty;
 
  for (size_t i = 0; i < N / 2; i++) {
    lgeom_bounds.grow(prims[start() + i].bounds());
    lcent_bounds.grow(prims[start() + i].bounds().center2());
  }
 
  for (size_t i = N / 2; i < N; i++) {
    rgeom_bounds.grow(prims[start() + i].bounds());
    rcent_bounds.grow(prims[start() + i].bounds().center2());
  }
 
  right_o = BVHObjectBinning(BVHRange(rgeom_bounds, rcent_bounds, start() + N / 2, N / 2 + N % 2),
                             prims);
  left_o = BVHObjectBinning(BVHRange(lgeom_bounds, lcent_bounds, start(), N / 2), prims);
}
 
CCL_NAMESPACE_END