bvh_params.h

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/*
 * Adapted from code copyright 2009-2010 NVIDIA Corporation
 * Modifications Copyright 2011, Blender Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
#ifndef __BVH_PARAMS_H__
#define __BVH_PARAMS_H__
 
#include "util/util_boundbox.h"
 
#include "kernel/kernel_types.h"
 
CCL_NAMESPACE_BEGIN
 
/* Layout of BVH tree.
 *
 * For example, how wide BVH tree is, in terms of number of children
 * per node.
 */
typedef KernelBVHLayout BVHLayout;
 
/* Names bitflag type to denote which BVH layouts are supported by
 * particular area.
 *
 * Bitflags are the BVH_LAYOUT_* values.
 */
typedef int BVHLayoutMask;
 
/* Get human readable name of BVH layout. */
const char *bvh_layout_name(BVHLayout layout);
 
/* BVH Parameters */
 
class BVHParams {
 public:
  /* spatial split area threshold */
  bool use_spatial_split;
  float spatial_split_alpha;
 
  /* Unaligned nodes creation threshold */
  float unaligned_split_threshold;
 
  /* SAH costs */
  float sah_node_cost;
  float sah_primitive_cost;
 
  /* number of primitives in leaf */
  int min_leaf_size;
  int max_triangle_leaf_size;
  int max_motion_triangle_leaf_size;
  int max_curve_leaf_size;
  int max_motion_curve_leaf_size;
 
  /* object or mesh level bvh */
  bool top_level;
 
  /* BVH layout to be built. */
  BVHLayout bvh_layout;
 
  /* Use unaligned bounding boxes.
   * Only used for curves BVH.
   */
  bool use_unaligned_nodes;
 
  /* Split time range to this number of steps and create leaf node for each
   * of this time steps.
   *
   * Speeds up rendering of motion curve primitives in the cost of higher
   * memory usage.
   */
  int num_motion_curve_steps;
 
  /* Same as above, but for triangle primitives. */
  int num_motion_triangle_steps;
 
  /* Same as in SceneParams. */
  int bvh_type;
 
  /* These are needed for Embree. */
  int curve_subdivisions;
 
  /* fixed parameters */
  enum { MAX_DEPTH = 64, MAX_SPATIAL_DEPTH = 48, NUM_SPATIAL_BINS = 32 };
 
  BVHParams()
  {
    use_spatial_split = true;
    spatial_split_alpha = 1e-5f;
 
    unaligned_split_threshold = 0.7f;
 
    /* todo: see if splitting up primitive cost to be separate for triangles
     * and curves can help. so far in tests it doesn't help, but why? */
    sah_node_cost = 1.0f;
    sah_primitive_cost = 1.0f;
 
    min_leaf_size = 1;
    max_triangle_leaf_size = 8;
    max_motion_triangle_leaf_size = 8;
    max_curve_leaf_size = 1;
    max_motion_curve_leaf_size = 4;
 
    top_level = false;
    bvh_layout = BVH_LAYOUT_BVH2;
    use_unaligned_nodes = false;
 
    num_motion_curve_steps = 0;
    num_motion_triangle_steps = 0;
 
    bvh_type = 0;
 
    curve_subdivisions = 4;
  }
 
  /* SAH costs */
  __forceinline float cost(int num_nodes, int num_primitives) const
  {
    return node_cost(num_nodes) + primitive_cost(num_primitives);
  }
 
  __forceinline float primitive_cost(int n) const
  {
    return n * sah_primitive_cost;
  }
 
  __forceinline float node_cost(int n) const
  {
    return n * sah_node_cost;
  }
 
  __forceinline bool small_enough_for_leaf(int size, int level)
  {
    return (size <= min_leaf_size || level >= MAX_DEPTH);
  }
 
  /* Gets best matching BVH.
   *
   * If the requested layout is supported by the device, it will be used.
   * Otherwise, widest supported layout below that will be used.
   */
  static BVHLayout best_bvh_layout(BVHLayout requested_layout, BVHLayoutMask supported_layouts);
};
 
/* BVH Reference
 *
 * Reference to a primitive. Primitive index and object are sneakily packed
 * into BoundBox to reduce memory usage and align nicely */
 
class BVHReference {
 public:
  __forceinline BVHReference()
  {
  }
 
  __forceinline BVHReference(const BoundBox &bounds_,
                             int prim_index_,
                             int prim_object_,
                             int prim_type,
                             float time_from = 0.0f,
                             float time_to = 1.0f)
      : rbounds(bounds_), time_from_(time_from), time_to_(time_to)
  {
    rbounds.min.w = __int_as_float(prim_index_);
    rbounds.max.w = __int_as_float(prim_object_);
    type = prim_type;
  }
 
  __forceinline const BoundBox &bounds() const
  {
    return rbounds;
  }
  __forceinline int prim_index() const
  {
    return __float_as_int(rbounds.min.w);
  }
  __forceinline int prim_object() const
  {
    return __float_as_int(rbounds.max.w);
  }
  __forceinline int prim_type() const
  {
    return type;
  }
  __forceinline float time_from() const
  {
    return time_from_;
  }
  __forceinline float time_to() const
  {
    return time_to_;
  }
 
  BVHReference &operator=(const BVHReference &arg)
  {
    if (&arg != this) {
      /* TODO(sergey): Check if it is still faster to memcpy() with
       * modern compilers.
       */
      memcpy((void *)this, &arg, sizeof(BVHReference));
    }
    return *this;
  }
 
 protected:
  BoundBox rbounds;
  uint type;
  float time_from_, time_to_;
};
 
/* BVH Range
 *
 * Build range used during construction, to indicate the bounds and place in
 * the reference array of a subset of primitives Again uses trickery to pack
 * integers into BoundBox for alignment purposes. */
 
class BVHRange {
 public:
  __forceinline BVHRange()
  {
    rbounds.min.w = __int_as_float(0);
    rbounds.max.w = __int_as_float(0);
  }
 
  __forceinline BVHRange(const BoundBox &bounds_, int start_, int size_) : rbounds(bounds_)
  {
    rbounds.min.w = __int_as_float(start_);
    rbounds.max.w = __int_as_float(size_);
  }
 
  __forceinline BVHRange(const BoundBox &bounds_, const BoundBox &cbounds_, int start_, int size_)
      : rbounds(bounds_), cbounds(cbounds_)
  {
    rbounds.min.w = __int_as_float(start_);
    rbounds.max.w = __int_as_float(size_);
  }
 
  __forceinline void set_start(int start_)
  {
    rbounds.min.w = __int_as_float(start_);
  }
 
  __forceinline const BoundBox &bounds() const
  {
    return rbounds;
  }
  __forceinline const BoundBox &cent_bounds() const
  {
    return cbounds;
  }
  __forceinline int start() const
  {
    return __float_as_int(rbounds.min.w);
  }
  __forceinline int size() const
  {
    return __float_as_int(rbounds.max.w);
  }
  __forceinline int end() const
  {
    return start() + size();
  }
 
 protected:
  BoundBox rbounds;
  BoundBox cbounds;
};
 
/* BVH Spatial Bin */
 
struct BVHSpatialBin {
  BoundBox bounds;
  int enter;
  int exit;
 
  __forceinline BVHSpatialBin()
  {
  }
};
 
/* BVH Spatial Storage
 *
 * The idea of this storage is have thread-specific storage for the spatial
 * splitters. We can pre-allocate this storage in advance and avoid heavy memory
 * operations during split process.
 */
 
struct BVHSpatialStorage {
  /* Accumulated bounds when sweeping from right to left.  */
  vector<BoundBox> right_bounds;
 
  /* Bins used for histogram when selecting best split plane. */
  BVHSpatialBin bins[3][BVHParams::NUM_SPATIAL_BINS];
 
  /* Temporary storage for the new references. Used by spatial split to store
   * new references in before they're getting inserted into actual array,
   */
  vector<BVHReference> new_references;
};
 
CCL_NAMESPACE_END
 
#endif /* __BVH_PARAMS_H__ */