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blender/intern/cycles/kernel/geom/geom_bvh.h
Brecht Van Lommel 9ab259f55b Cycles: shadow function optimization for transparent shadows (CPU only). 
Old algorithm:

Raytrace from one transparent surface to the next step by step. To minimize
overhead in cases where we don't need transparent shadows, we first trace a
regular shadow ray. We check if the hit primitive was potentially transparent,
and only in that case start marching. this gives extra ray cast for the cases
were we do want transparency.

New algorithm:

We trace a single ray. If it hits any opaque surface, or more than a given
number of transparent surfaces is hit, then we consider the geometry to be
entirely blocked. If not, all transparent surfaces will be recorded and we
will shade them one by one to determine how much light is blocked. This all
happens in one scene intersection function.

Recording all hits works well in some cases but may be slower in others. If
we have many semi-transparent hairs, one intersection may be faster because
you'd be reinteresecting the same hairs a lot with each step otherwise. If
however there is mostly binary transparency then we may be recording many
unnecessary intersections when one of the first surfaces blocks all light.

We found that this helps quite nicely in some scenes, on koro.blend this can
give a 50% reduction in render time, on the pabellon barcelona scene and a
forest scene with transparent leaves it was 30%. Some other files rendered
maybe 1% or 2% slower, but this seems a reasonable tradeoff.

Differential Revision: https://developer.blender.org/D473
2014-04-21 19:34:25 +02:00

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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.
*/
/* BVH
*
* Bounding volume hierarchy for ray tracing. We compile different variations
* of the same BVH traversal function for faster rendering when some types of
* primitives are not needed, using #includes to work around the lack of
* C++ templates in OpenCL.
*
* Originally based on "Understanding the Efficiency of Ray Traversal on GPUs",
* the code has been extended and modified to support more primitives and work
* with CPU/CUDA/OpenCL. */
CCL_NAMESPACE_BEGIN
/* BVH intersection function variations */
#define BVH_INSTANCING 1
#define BVH_MOTION 2
#define BVH_HAIR 4
#define BVH_HAIR_MINIMUM_WIDTH 8
#define BVH_FUNCTION_NAME bvh_intersect
#define BVH_FUNCTION_FEATURES 0
#include "geom_bvh_traversal.h"
#if defined(__INSTANCING__)
#define BVH_FUNCTION_NAME bvh_intersect_instancing
#define BVH_FUNCTION_FEATURES BVH_INSTANCING
#include "geom_bvh_traversal.h"
#endif
#if defined(__HAIR__)
#define BVH_FUNCTION_NAME bvh_intersect_hair
#define BVH_FUNCTION_FEATURES BVH_INSTANCING|BVH_HAIR|BVH_HAIR_MINIMUM_WIDTH
#include "geom_bvh_traversal.h"
#endif
#if defined(__OBJECT_MOTION__)
#define BVH_FUNCTION_NAME bvh_intersect_motion
#define BVH_FUNCTION_FEATURES BVH_INSTANCING|BVH_MOTION
#include "geom_bvh_traversal.h"
#endif
#if defined(__HAIR__) && defined(__OBJECT_MOTION__)
#define BVH_FUNCTION_NAME bvh_intersect_hair_motion
#define BVH_FUNCTION_FEATURES BVH_INSTANCING|BVH_HAIR|BVH_HAIR_MINIMUM_WIDTH|BVH_MOTION
#include "geom_bvh_traversal.h"
#endif
#if defined(__SUBSURFACE__)
#define BVH_FUNCTION_NAME bvh_intersect_subsurface
#define BVH_FUNCTION_FEATURES 0
#include "geom_bvh_subsurface.h"
#endif
#if defined(__SUBSURFACE__) && defined(__INSTANCING__)
#define BVH_FUNCTION_NAME bvh_intersect_subsurface_instancing
#define BVH_FUNCTION_FEATURES BVH_INSTANCING
#include "geom_bvh_subsurface.h"
#endif
#if defined(__SUBSURFACE__) && defined(__HAIR__)
#define BVH_FUNCTION_NAME bvh_intersect_subsurface_hair
#define BVH_FUNCTION_FEATURES BVH_INSTANCING|BVH_HAIR
#include "geom_bvh_subsurface.h"
#endif
#if defined(__SUBSURFACE__) && defined(__OBJECT_MOTION__)
#define BVH_FUNCTION_NAME bvh_intersect_subsurface_motion
#define BVH_FUNCTION_FEATURES BVH_INSTANCING|BVH_MOTION
#include "geom_bvh_subsurface.h"
#endif
#if defined(__SUBSURFACE__) && defined(__HAIR__) && defined(__OBJECT_MOTION__)
#define BVH_FUNCTION_NAME bvh_intersect_subsurface_hair_motion
#define BVH_FUNCTION_FEATURES BVH_INSTANCING|BVH_HAIR|BVH_MOTION
#include "geom_bvh_subsurface.h"
#endif
#if defined(__SHADOW_RECORD_ALL__)
#define BVH_FUNCTION_NAME bvh_intersect_shadow_all
#define BVH_FUNCTION_FEATURES 0
#include "geom_bvh_shadow.h"
#endif
#if defined(__SUBSURFACE__) && defined(__INSTANCING__)
#define BVH_FUNCTION_NAME bvh_intersect_shadow_all_instancing
#define BVH_FUNCTION_FEATURES BVH_INSTANCING
#include "geom_bvh_shadow.h"
#endif
#if defined(__SUBSURFACE__) && defined(__HAIR__)
#define BVH_FUNCTION_NAME bvh_intersect_shadow_all_hair
#define BVH_FUNCTION_FEATURES BVH_INSTANCING|BVH_HAIR
#include "geom_bvh_shadow.h"
#endif
#if defined(__SUBSURFACE__) && defined(__OBJECT_MOTION__)
#define BVH_FUNCTION_NAME bvh_intersect_shadow_all_motion
#define BVH_FUNCTION_FEATURES BVH_INSTANCING|BVH_MOTION
#include "geom_bvh_shadow.h"
#endif
#if defined(__SUBSURFACE__) && defined(__HAIR__) && defined(__OBJECT_MOTION__)
#define BVH_FUNCTION_NAME bvh_intersect_shadow_all_hair_motion
#define BVH_FUNCTION_FEATURES BVH_INSTANCING|BVH_HAIR|BVH_MOTION
#include "geom_bvh_shadow.h"
#endif
/* to work around titan bug when using arrays instead of textures */
#if !defined(__KERNEL_CUDA__) || defined(__KERNEL_CUDA_TEX_STORAGE__)
ccl_device_inline
#else
ccl_device_noinline
#endif
#ifdef __HAIR__
bool scene_intersect(KernelGlobals *kg, const Ray *ray, const uint visibility, Intersection *isect, uint *lcg_state, float difl, float extmax)
#else
bool scene_intersect(KernelGlobals *kg, const Ray *ray, const uint visibility, Intersection *isect)
#endif
{
#ifdef __OBJECT_MOTION__
if(kernel_data.bvh.have_motion) {
#ifdef __HAIR__
if(kernel_data.bvh.have_curves)
return bvh_intersect_hair_motion(kg, ray, isect, visibility, lcg_state, difl, extmax);
#endif /* __HAIR__ */
return bvh_intersect_motion(kg, ray, isect, visibility);
}
#endif /* __OBJECT_MOTION__ */
#ifdef __HAIR__
if(kernel_data.bvh.have_curves)
return bvh_intersect_hair(kg, ray, isect, visibility, lcg_state, difl, extmax);
#endif /* __HAIR__ */
#ifdef __KERNEL_CPU__
#ifdef __INSTANCING__
if(kernel_data.bvh.have_instancing)
return bvh_intersect_instancing(kg, ray, isect, visibility);
#endif /* __INSTANCING__ */
return bvh_intersect(kg, ray, isect, visibility);
#else /* __KERNEL_CPU__ */
#ifdef __INSTANCING__
return bvh_intersect_instancing(kg, ray, isect, visibility);
#else
return bvh_intersect(kg, ray, isect, visibility);
#endif /* __INSTANCING__ */
#endif /* __KERNEL_CPU__ */
}
/* to work around titan bug when using arrays instead of textures */
#ifdef __SUBSURFACE__
#if !defined(__KERNEL_CUDA__) || defined(__KERNEL_CUDA_TEX_STORAGE__)
ccl_device_inline
#else
ccl_device_noinline
#endif
uint scene_intersect_subsurface(KernelGlobals *kg, const Ray *ray, Intersection *isect, int subsurface_object, uint *lcg_state, int max_hits)
{
#ifdef __OBJECT_MOTION__
if(kernel_data.bvh.have_motion) {
#ifdef __HAIR__
if(kernel_data.bvh.have_curves)
return bvh_intersect_subsurface_hair_motion(kg, ray, isect, subsurface_object, lcg_state, max_hits);
#endif /* __HAIR__ */
return bvh_intersect_subsurface_motion(kg, ray, isect, subsurface_object, lcg_state, max_hits);
}
#endif /* __OBJECT_MOTION__ */
#ifdef __HAIR__
if(kernel_data.bvh.have_curves)
return bvh_intersect_subsurface_hair(kg, ray, isect, subsurface_object, lcg_state, max_hits);
#endif /* __HAIR__ */
#ifdef __KERNEL_CPU__
#ifdef __INSTANCING__
if(kernel_data.bvh.have_instancing)
return bvh_intersect_subsurface_instancing(kg, ray, isect, subsurface_object, lcg_state, max_hits);
#endif /* __INSTANCING__ */
return bvh_intersect_subsurface(kg, ray, isect, subsurface_object, lcg_state, max_hits);
#else /* __KERNEL_CPU__ */
#ifdef __INSTANCING__
return bvh_intersect_subsurface_instancing(kg, ray, isect, subsurface_object, lcg_state, max_hits);
#else
return bvh_intersect_subsurface(kg, ray, isect, subsurface_object, lcg_state, max_hits);
#endif /* __INSTANCING__ */
#endif /* __KERNEL_CPU__ */
}
#endif
/* to work around titan bug when using arrays instead of textures */
#ifdef __SHADOW_RECORD_ALL__
#if !defined(__KERNEL_CUDA__) || defined(__KERNEL_CUDA_TEX_STORAGE__)
ccl_device_inline
#else
ccl_device_noinline
#endif
uint scene_intersect_shadow_all(KernelGlobals *kg, const Ray *ray, Intersection *isect, uint max_hits, uint *num_hits)
{
#ifdef __OBJECT_MOTION__
if(kernel_data.bvh.have_motion) {
#ifdef __HAIR__
if(kernel_data.bvh.have_curves)
return bvh_intersect_shadow_all_hair_motion(kg, ray, isect, max_hits, num_hits);
#endif /* __HAIR__ */
return bvh_intersect_shadow_all_motion(kg, ray, isect, max_hits, num_hits);
}
#endif /* __OBJECT_MOTION__ */
#ifdef __HAIR__
if(kernel_data.bvh.have_curves)
return bvh_intersect_shadow_all_hair(kg, ray, isect, max_hits, num_hits);
#endif /* __HAIR__ */
#ifdef __KERNEL_CPU__
#ifdef __INSTANCING__
if(kernel_data.bvh.have_instancing)
return bvh_intersect_shadow_all_instancing(kg, ray, isect, max_hits, num_hits);
#endif /* __INSTANCING__ */
return bvh_intersect_shadow_all(kg, ray, isect, max_hits, num_hits);
#else /* __KERNEL_CPU__ */
#ifdef __INSTANCING__
return bvh_intersect_shadow_all_instancing(kg, ray, isect, max_hits, num_hits);
#else
return bvh_intersect_shadow_all(kg, ray, isect, max_hits, num_hits);
#endif /* __INSTANCING__ */
#endif /* __KERNEL_CPU__ */
}
#endif
/* Ray offset to avoid self intersection.
*
* This function should be used to compute a modified ray start position for
* rays leaving from a surface. */
ccl_device_inline float3 ray_offset(float3 P, float3 Ng)
{
#ifdef __INTERSECTION_REFINE__
const float epsilon_f = 1e-5f;
/* ideally this should match epsilon_f, but instancing and motion blur
* precision makes it problematic */
const float epsilon_test = 1.0f;
const int epsilon_i = 32;
float3 res;
/* x component */
if(fabsf(P.x) < epsilon_test) {
res.x = P.x + Ng.x*epsilon_f;
}
else {
uint ix = __float_as_uint(P.x);
ix += ((ix ^ __float_as_uint(Ng.x)) >> 31)? -epsilon_i: epsilon_i;
res.x = __uint_as_float(ix);
}
/* y component */
if(fabsf(P.y) < epsilon_test) {
res.y = P.y + Ng.y*epsilon_f;
}
else {
uint iy = __float_as_uint(P.y);
iy += ((iy ^ __float_as_uint(Ng.y)) >> 31)? -epsilon_i: epsilon_i;
res.y = __uint_as_float(iy);
}
/* z component */
if(fabsf(P.z) < epsilon_test) {
res.z = P.z + Ng.z*epsilon_f;
}
else {
uint iz = __float_as_uint(P.z);
iz += ((iz ^ __float_as_uint(Ng.z)) >> 31)? -epsilon_i: epsilon_i;
res.z = __uint_as_float(iz);
}
return res;
#else
const float epsilon_f = 1e-4f;
return P + epsilon_f*Ng;
#endif
}
CCL_NAMESPACE_END
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