Brecht Van Lommel
0df9b2c715
It is basically brute force volume scattering within the mesh, but part of the SSS code for faster performance. The main difference with actual volume scattering is that we assume the boundaries are diffuse and that all lighting is coming through this boundary from outside the volume. This gives much more accurate results for thin features and low density. Some challenges remain however: * Significantly more noisy than BSSRDF. Adding Dwivedi sampling may help here, but it's unclear still how much it helps in real world cases. * Due to this being a volumetric method, geometry like eyes or mouth can darken the skin on the outside. We may be able to reduce this effect, or users can compensate for it by reducing the scattering radius in such areas. * Sharp corners are quite bright. This matches actual volume rendering and results in some other renderers, but maybe not so much real world objects. Differential Revision: https://developer.blender.org/D3054
313 lines
9.7 KiB
C++
313 lines
9.7 KiB
C++
/*
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* Copyright 2014, Blender Foundation.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/* Triangle/Ray intersections.
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*
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* For BVH ray intersection we use a precomputed triangle storage to accelerate
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* intersection at the cost of more memory usage.
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*/
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CCL_NAMESPACE_BEGIN
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ccl_device_inline bool triangle_intersect(KernelGlobals *kg,
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Intersection *isect,
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float3 P,
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float3 dir,
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uint visibility,
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int object,
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int prim_addr)
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{
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const uint tri_vindex = kernel_tex_fetch(__prim_tri_index, prim_addr);
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#if defined(__KERNEL_SSE2__) && defined(__KERNEL_SSE__)
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const ssef *ssef_verts = (ssef*)&kg->__prim_tri_verts.data[tri_vindex];
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#else
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const float4 tri_a = kernel_tex_fetch(__prim_tri_verts, tri_vindex+0),
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tri_b = kernel_tex_fetch(__prim_tri_verts, tri_vindex+1),
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tri_c = kernel_tex_fetch(__prim_tri_verts, tri_vindex+2);
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#endif
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float t, u, v;
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if(ray_triangle_intersect(P,
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dir,
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isect->t,
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#if defined(__KERNEL_SSE2__) && defined(__KERNEL_SSE__)
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ssef_verts,
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#else
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float4_to_float3(tri_a),
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float4_to_float3(tri_b),
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float4_to_float3(tri_c),
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#endif
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&u, &v, &t))
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{
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#ifdef __VISIBILITY_FLAG__
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/* Visibility flag test. we do it here under the assumption
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* that most triangles are culled by node flags.
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*/
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if(kernel_tex_fetch(__prim_visibility, prim_addr) & visibility)
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#endif
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{
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isect->prim = prim_addr;
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isect->object = object;
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isect->type = PRIMITIVE_TRIANGLE;
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isect->u = u;
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isect->v = v;
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isect->t = t;
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return true;
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}
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}
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return false;
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}
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/* Special ray intersection routines for local intersection. In that case we
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* only want to intersect with primitives in the same object, and if case of
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* multiple hits we pick a single random primitive as the intersection point.
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*/
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#ifdef __BVH_LOCAL__
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ccl_device_inline void triangle_intersect_local(
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KernelGlobals *kg,
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LocalIntersection *local_isect,
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float3 P,
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float3 dir,
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int object,
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int local_object,
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int prim_addr,
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float tmax,
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uint *lcg_state,
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int max_hits)
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{
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/* Only intersect with matching object, for instanced objects we
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* already know we are only intersecting the right object. */
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if(object == OBJECT_NONE) {
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if(kernel_tex_fetch(__prim_object, prim_addr) != local_object) {
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return;
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}
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}
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const uint tri_vindex = kernel_tex_fetch(__prim_tri_index, prim_addr);
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#if defined(__KERNEL_SSE2__) && defined(__KERNEL_SSE__)
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const ssef *ssef_verts = (ssef*)&kg->__prim_tri_verts.data[tri_vindex];
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#else
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const float3 tri_a = float4_to_float3(kernel_tex_fetch(__prim_tri_verts, tri_vindex+0)),
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tri_b = float4_to_float3(kernel_tex_fetch(__prim_tri_verts, tri_vindex+1)),
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tri_c = float4_to_float3(kernel_tex_fetch(__prim_tri_verts, tri_vindex+2));
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#endif
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float t, u, v;
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if(!ray_triangle_intersect(P,
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dir,
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tmax,
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#if defined(__KERNEL_SSE2__) && defined(__KERNEL_SSE__)
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ssef_verts,
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#else
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tri_a, tri_b, tri_c,
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#endif
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&u, &v, &t))
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{
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return;
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}
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int hit;
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if(lcg_state) {
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/* Record up to max_hits intersections. */
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for(int i = min(max_hits, local_isect->num_hits) - 1; i >= 0; --i) {
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if(local_isect->hits[i].t == t) {
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return;
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}
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}
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local_isect->num_hits++;
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if(local_isect->num_hits <= max_hits) {
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hit = local_isect->num_hits - 1;
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}
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else {
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/* reservoir sampling: if we are at the maximum number of
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* hits, randomly replace element or skip it */
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hit = lcg_step_uint(lcg_state) % local_isect->num_hits;
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if(hit >= max_hits)
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return;
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}
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}
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else {
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/* Record closest intersection only. */
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if(local_isect->num_hits && t > local_isect->hits[0].t) {
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return;
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}
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hit = 0;
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local_isect->num_hits = 1;
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}
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/* Record intersection. */
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Intersection *isect = &local_isect->hits[hit];
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isect->prim = prim_addr;
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isect->object = object;
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isect->type = PRIMITIVE_TRIANGLE;
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isect->u = u;
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isect->v = v;
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isect->t = t;
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/* Record geometric normal. */
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#if defined(__KERNEL_SSE2__) && defined(__KERNEL_SSE__)
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const float3 tri_a = float4_to_float3(kernel_tex_fetch(__prim_tri_verts, tri_vindex+0)),
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tri_b = float4_to_float3(kernel_tex_fetch(__prim_tri_verts, tri_vindex+1)),
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tri_c = float4_to_float3(kernel_tex_fetch(__prim_tri_verts, tri_vindex+2));
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#endif
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local_isect->Ng[hit] = normalize(cross(tri_b - tri_a, tri_c - tri_a));
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}
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#endif /* __BVH_LOCAL__ */
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/* Refine triangle intersection to more precise hit point. For rays that travel
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* far the precision is often not so good, this reintersects the primitive from
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* a closer distance. */
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/* Reintersections uses the paper:
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*
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* Tomas Moeller
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* Fast, minimum storage ray/triangle intersection
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* http://www.cs.virginia.edu/~gfx/Courses/2003/ImageSynthesis/papers/Acceleration/Fast%20MinimumStorage%20RayTriangle%20Intersection.pdf
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*/
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ccl_device_inline float3 triangle_refine(KernelGlobals *kg,
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ShaderData *sd,
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const Intersection *isect,
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const Ray *ray)
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{
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float3 P = ray->P;
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float3 D = ray->D;
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float t = isect->t;
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#ifdef __INTERSECTION_REFINE__
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if(isect->object != OBJECT_NONE) {
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if(UNLIKELY(t == 0.0f)) {
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return P;
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}
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# ifdef __OBJECT_MOTION__
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Transform tfm = sd->ob_itfm;
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# else
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Transform tfm = object_fetch_transform(kg, isect->object, OBJECT_INVERSE_TRANSFORM);
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# endif
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P = transform_point(&tfm, P);
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D = transform_direction(&tfm, D*t);
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D = normalize_len(D, &t);
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}
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P = P + D*t;
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const uint tri_vindex = kernel_tex_fetch(__prim_tri_index, isect->prim);
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const float4 tri_a = kernel_tex_fetch(__prim_tri_verts, tri_vindex+0),
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tri_b = kernel_tex_fetch(__prim_tri_verts, tri_vindex+1),
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tri_c = kernel_tex_fetch(__prim_tri_verts, tri_vindex+2);
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float3 edge1 = make_float3(tri_a.x - tri_c.x, tri_a.y - tri_c.y, tri_a.z - tri_c.z);
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float3 edge2 = make_float3(tri_b.x - tri_c.x, tri_b.y - tri_c.y, tri_b.z - tri_c.z);
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float3 tvec = make_float3(P.x - tri_c.x, P.y - tri_c.y, P.z - tri_c.z);
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float3 qvec = cross(tvec, edge1);
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float3 pvec = cross(D, edge2);
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float det = dot(edge1, pvec);
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if(det != 0.0f) {
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/* If determinant is zero it means ray lies in the plane of
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* the triangle. It is possible in theory due to watertight
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* nature of triangle intersection. For such cases we simply
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* don't refine intersection hoping it'll go all fine.
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*/
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float rt = dot(edge2, qvec) / det;
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P = P + D*rt;
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}
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if(isect->object != OBJECT_NONE) {
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# ifdef __OBJECT_MOTION__
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Transform tfm = sd->ob_tfm;
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# else
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Transform tfm = object_fetch_transform(kg, isect->object, OBJECT_TRANSFORM);
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# endif
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P = transform_point(&tfm, P);
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}
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return P;
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#else
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return P + D*t;
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#endif
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}
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/* Same as above, except that isect->t is assumed to be in object space for
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* instancing.
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*/
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ccl_device_inline float3 triangle_refine_local(KernelGlobals *kg,
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ShaderData *sd,
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const Intersection *isect,
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const Ray *ray)
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{
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float3 P = ray->P;
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float3 D = ray->D;
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float t = isect->t;
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if(isect->object != OBJECT_NONE) {
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#ifdef __OBJECT_MOTION__
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Transform tfm = sd->ob_itfm;
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#else
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Transform tfm = object_fetch_transform(kg,
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isect->object,
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OBJECT_INVERSE_TRANSFORM);
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#endif
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P = transform_point(&tfm, P);
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D = transform_direction(&tfm, D);
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D = normalize(D);
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}
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P = P + D*t;
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#ifdef __INTERSECTION_REFINE__
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const uint tri_vindex = kernel_tex_fetch(__prim_tri_index, isect->prim);
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const float4 tri_a = kernel_tex_fetch(__prim_tri_verts, tri_vindex+0),
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tri_b = kernel_tex_fetch(__prim_tri_verts, tri_vindex+1),
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tri_c = kernel_tex_fetch(__prim_tri_verts, tri_vindex+2);
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float3 edge1 = make_float3(tri_a.x - tri_c.x, tri_a.y - tri_c.y, tri_a.z - tri_c.z);
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float3 edge2 = make_float3(tri_b.x - tri_c.x, tri_b.y - tri_c.y, tri_b.z - tri_c.z);
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float3 tvec = make_float3(P.x - tri_c.x, P.y - tri_c.y, P.z - tri_c.z);
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float3 qvec = cross(tvec, edge1);
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float3 pvec = cross(D, edge2);
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float det = dot(edge1, pvec);
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if(det != 0.0f) {
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/* If determinant is zero it means ray lies in the plane of
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* the triangle. It is possible in theory due to watertight
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* nature of triangle intersection. For such cases we simply
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* don't refine intersection hoping it'll go all fine.
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*/
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float rt = dot(edge2, qvec) / det;
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P = P + D*rt;
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}
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#endif /* __INTERSECTION_REFINE__ */
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if(isect->object != OBJECT_NONE) {
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#ifdef __OBJECT_MOTION__
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Transform tfm = sd->ob_tfm;
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#else
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Transform tfm = object_fetch_transform(kg,
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isect->object,
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OBJECT_TRANSFORM);
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#endif
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P = transform_point(&tfm, P);
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}
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return P;
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}
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CCL_NAMESPACE_END
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