/* SPDX-License-Identifier: Apache-2.0
 * Adapted from code Copyright 2009-2010 NVIDIA Corporation,
 * and code copyright 2009-2012 Intel Corporation
 *
 * Modifications Copyright 2011-2022 Blender Foundation. */

#if BVH_FEATURE(BVH_HAIR)
#  define NODE_INTERSECT bvh_node_intersect
#else
#  define NODE_INTERSECT bvh_aligned_node_intersect
#endif

/* This is a template BVH traversal function, where various features can be
 * enabled/disabled. This way we can compile optimized versions for each case
 * without new features slowing things down.
 *
 * BVH_HAIR: hair curve rendering
 * BVH_POINTCLOUD: point cloud rendering
 * BVH_MOTION: motion blur rendering
 */

#ifndef __KERNEL_GPU__
ccl_device
#else
ccl_device_inline
#endif
    bool BVH_FUNCTION_FULL_NAME(BVH)(KernelGlobals kg,
                                     ccl_private const Ray *ray,
                                     IntegratorShadowState state,
                                     const uint visibility,
                                     const uint max_hits,
                                     ccl_private uint *r_num_recorded_hits,
                                     ccl_private float *r_throughput)
{
  /* todo:
   * - likely and unlikely for if() statements
   * - test restrict attribute for pointers
   */

  /* traversal stack in CUDA thread-local memory */
  int traversal_stack[BVH_STACK_SIZE];
  traversal_stack[0] = ENTRYPOINT_SENTINEL;

  /* traversal variables in registers */
  int stack_ptr = 0;
  int node_addr = kernel_data.bvh.root;

  /* ray parameters in registers */
  float3 P = ray->P;
  float3 dir = bvh_clamp_direction(ray->D);
  float3 idir = bvh_inverse_direction(dir);
  float tmin = ray->tmin;
  int object = OBJECT_NONE;
  uint num_hits = 0;

  /* Max distance in world space. May be dynamically reduced when max number of
   * recorded hits is exceeded and we no longer need to find hits beyond the max
   * distance found. */
  const float tmax = ray->tmax;
  float tmax_hits = tmax;

  *r_num_recorded_hits = 0;
  *r_throughput = 1.0f;

  /* traversal loop */
  do {
    do {
      /* traverse internal nodes */
      while (node_addr >= 0 && node_addr != ENTRYPOINT_SENTINEL) {
        int node_addr_child1, traverse_mask;
        float dist[2];
        float4 cnodes = kernel_data_fetch(bvh_nodes, node_addr + 0);

        traverse_mask = NODE_INTERSECT(kg,
                                       P,
#if BVH_FEATURE(BVH_HAIR)
                                       dir,
#endif
                                       idir,
                                       tmin,
                                       tmax,
                                       node_addr,
                                       visibility,
                                       dist);

        node_addr = __float_as_int(cnodes.z);
        node_addr_child1 = __float_as_int(cnodes.w);

        if (traverse_mask == 3) {
          /* Both children were intersected, push the farther one. */
          bool is_closest_child1 = (dist[1] < dist[0]);
          if (is_closest_child1) {
            int tmp = node_addr;
            node_addr = node_addr_child1;
            node_addr_child1 = tmp;
          }

          ++stack_ptr;
          kernel_assert(stack_ptr < BVH_STACK_SIZE);
          traversal_stack[stack_ptr] = node_addr_child1;
        }
        else {
          /* One child was intersected. */
          if (traverse_mask == 2) {
            node_addr = node_addr_child1;
          }
          else if (traverse_mask == 0) {
            /* Neither child was intersected. */
            node_addr = traversal_stack[stack_ptr];
            --stack_ptr;
          }
        }
      }

      /* if node is leaf, fetch triangle list */
      if (node_addr < 0) {
        float4 leaf = kernel_data_fetch(bvh_leaf_nodes, (-node_addr - 1));
        int prim_addr = __float_as_int(leaf.x);

        if (prim_addr >= 0) {
          const int prim_addr2 = __float_as_int(leaf.y);
          const uint type = __float_as_int(leaf.w);

          /* pop */
          node_addr = traversal_stack[stack_ptr];
          --stack_ptr;

          /* primitive intersection */
          for (; prim_addr < prim_addr2; prim_addr++) {
            kernel_assert((kernel_data_fetch(prim_type, prim_addr) & PRIMITIVE_ALL) ==
                          (type & PRIMITIVE_ALL));
            bool hit;

            /* todo: specialized intersect functions which don't fill in
             * isect unless needed and check SD_HAS_TRANSPARENT_SHADOW?
             * might give a few % performance improvement */
            Intersection isect ccl_optional_struct_init;

            const int prim_object = (object == OBJECT_NONE) ?
                                        kernel_data_fetch(prim_object, prim_addr) :
                                        object;
            const int prim = kernel_data_fetch(prim_index, prim_addr);
            if (intersection_skip_self_shadow(ray->self, prim_object, prim)) {
              continue;
            }

            switch (type & PRIMITIVE_ALL) {
              case PRIMITIVE_TRIANGLE: {
                hit = triangle_intersect(
                    kg, &isect, P, dir, tmin, tmax, visibility, prim_object, prim, prim_addr);
                break;
              }
#if BVH_FEATURE(BVH_MOTION)
              case PRIMITIVE_MOTION_TRIANGLE: {
                hit = motion_triangle_intersect(kg,
                                                &isect,
                                                P,
                                                dir,
                                                tmin,
                                                tmax,
                                                ray->time,
                                                visibility,
                                                prim_object,
                                                prim,
                                                prim_addr);
                break;
              }
#endif
#if BVH_FEATURE(BVH_HAIR)
              case PRIMITIVE_CURVE_THICK:
              case PRIMITIVE_MOTION_CURVE_THICK:
              case PRIMITIVE_CURVE_RIBBON:
              case PRIMITIVE_MOTION_CURVE_RIBBON: {
                if ((type & PRIMITIVE_MOTION) && kernel_data.bvh.use_bvh_steps) {
                  const float2 prim_time = kernel_data_fetch(prim_time, prim_addr);
                  if (ray->time < prim_time.x || ray->time > prim_time.y) {
                    hit = false;
                    break;
                  }
                }

                const int curve_type = kernel_data_fetch(prim_type, prim_addr);
                hit = curve_intersect(
                    kg, &isect, P, dir, tmin, tmax, prim_object, prim, ray->time, curve_type);

                break;
              }
#endif
#if BVH_FEATURE(BVH_POINTCLOUD)
              case PRIMITIVE_POINT:
              case PRIMITIVE_MOTION_POINT: {
                if ((type & PRIMITIVE_MOTION) && kernel_data.bvh.use_bvh_steps) {
                  const float2 prim_time = kernel_data_fetch(prim_time, prim_addr);
                  if (ray->time < prim_time.x || ray->time > prim_time.y) {
                    hit = false;
                    break;
                  }
                }

                const int point_type = kernel_data_fetch(prim_type, prim_addr);
                hit = point_intersect(
                    kg, &isect, P, dir, tmin, tmax, prim_object, prim, ray->time, point_type);
                break;
              }
#endif /* BVH_FEATURE(BVH_POINTCLOUD) */
              default: {
                hit = false;
                break;
              }
            }

            /* shadow ray early termination */
            if (hit) {
              /* detect if this surface has a shader with transparent shadows */
              /* todo: optimize so primitive visibility flag indicates if
               * the primitive has a transparent shadow shader? */
              const int flags = intersection_get_shader_flags(kg, isect.prim, isect.type);

              if (!(flags & SD_HAS_TRANSPARENT_SHADOW) || num_hits >= max_hits) {
                /* If no transparent shadows, all light is blocked and we can
                 * stop immediately. */
                return true;
              }

              num_hits++;

              bool record_intersection = true;

              /* Always use baked shadow transparency for curves. */
              if (isect.type & PRIMITIVE_CURVE) {
                *r_throughput *= intersection_curve_shadow_transparency(
                    kg, isect.object, isect.prim, isect.type, isect.u);

                if (*r_throughput < CURVE_SHADOW_TRANSPARENCY_CUTOFF) {
                  return true;
                }
                else {
                  record_intersection = false;
                }
              }

              if (record_intersection) {
                /* Test if we need to record this transparent intersection. */
                const uint max_record_hits = min(max_hits, INTEGRATOR_SHADOW_ISECT_SIZE);
                if (*r_num_recorded_hits < max_record_hits || isect.t < tmax_hits) {
                  /* If maximum number of hits was reached, replace the intersection with the
                   * highest distance. We want to find the N closest intersections. */
                  const uint num_recorded_hits = min(*r_num_recorded_hits, max_record_hits);
                  uint isect_index = num_recorded_hits;
                  if (num_recorded_hits + 1 >= max_record_hits) {
                    float max_t = INTEGRATOR_STATE_ARRAY(state, shadow_isect, 0, t);
                    uint max_recorded_hit = 0;

                    for (uint i = 1; i < num_recorded_hits; ++i) {
                      const float isect_t = INTEGRATOR_STATE_ARRAY(state, shadow_isect, i, t);
                      if (isect_t > max_t) {
                        max_recorded_hit = i;
                        max_t = isect_t;
                      }
                    }

                    if (num_recorded_hits >= max_record_hits) {
                      isect_index = max_recorded_hit;
                    }

                    /* Limit the ray distance and stop counting hits beyond this. */
                    tmax_hits = max(isect.t, max_t);
                  }

                  integrator_state_write_shadow_isect(state, &isect, isect_index);
                }

                /* Always increase the number of recorded hits, even beyond the maximum,
                 * so that we can detect this and trace another ray if needed. */
                ++(*r_num_recorded_hits);
              }
            }
          }
        }
        else {
          /* instance push */
          object = kernel_data_fetch(prim_object, -prim_addr - 1);

#if BVH_FEATURE(BVH_MOTION)
          bvh_instance_motion_push(kg, object, ray, &P, &dir, &idir);
#else
          bvh_instance_push(kg, object, ray, &P, &dir, &idir);
#endif

          ++stack_ptr;
          kernel_assert(stack_ptr < BVH_STACK_SIZE);
          traversal_stack[stack_ptr] = ENTRYPOINT_SENTINEL;

          node_addr = kernel_data_fetch(object_node, object);
        }
      }
    } while (node_addr != ENTRYPOINT_SENTINEL);

    if (stack_ptr >= 0) {
      kernel_assert(object != OBJECT_NONE);

      /* Instance pop. */
      bvh_instance_pop(ray, &P, &dir, &idir);

      object = OBJECT_NONE;
      node_addr = traversal_stack[stack_ptr];
      --stack_ptr;
    }
  } while (node_addr != ENTRYPOINT_SENTINEL);

  return false;
}

ccl_device_inline bool BVH_FUNCTION_NAME(KernelGlobals kg,
                                         ccl_private const Ray *ray,
                                         IntegratorShadowState state,
                                         const uint visibility,
                                         const uint max_hits,
                                         ccl_private uint *num_recorded_hits,
                                         ccl_private float *throughput)
{
  return BVH_FUNCTION_FULL_NAME(BVH)(
      kg, ray, state, visibility, max_hits, num_recorded_hits, throughput);
}

#undef BVH_FUNCTION_NAME
#undef BVH_FUNCTION_FEATURES
#undef NODE_INTERSECT
