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
314 lines
8.5 KiB
C++
314 lines
8.5 KiB
C++
/*
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* Copyright 2011-2016 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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/* Motion Triangle Primitive
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*
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* These are stored as regular triangles, plus extra positions and normals at
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* times other than the frame center. Computing the triangle vertex positions
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* or normals at a given ray time is a matter of interpolation of the two steps
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* between which the ray time lies.
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*
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* The extra positions and normals are stored as ATTR_STD_MOTION_VERTEX_POSITION
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* and ATTR_STD_MOTION_VERTEX_NORMAL mesh attributes.
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*/
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CCL_NAMESPACE_BEGIN
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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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*/
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ccl_device_inline float3 motion_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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float3 verts[3])
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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,
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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*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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/* Compute refined intersection distance. */
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const float3 e1 = verts[0] - verts[2];
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const float3 e2 = verts[1] - verts[2];
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const float3 s1 = cross(D, e2);
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const float invdivisor = 1.0f/dot(s1, e1);
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const float3 d = P - verts[2];
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const float3 s2 = cross(d, e1);
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float rt = dot(e2, s2)*invdivisor;
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/* Compute refined position. */
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P = P + D*rt;
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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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#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
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* for instancing.
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*/
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#ifdef __BVH_LOCAL__
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# if defined(__KERNEL_CUDA__) && (defined(i386) || defined(_M_IX86))
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ccl_device_noinline
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# else
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ccl_device_inline
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# endif
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float3 motion_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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float3 verts[3])
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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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# 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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/* compute refined intersection distance */
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const float3 e1 = verts[0] - verts[2];
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const float3 e2 = verts[1] - verts[2];
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const float3 s1 = cross(D, e2);
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const float invdivisor = 1.0f/dot(s1, e1);
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const float3 d = P - verts[2];
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const float3 s2 = cross(d, e1);
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float rt = dot(e2, s2)*invdivisor;
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P = P + D*rt;
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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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# else /* __INTERSECTION_REFINE__ */
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return P + D*t;
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# endif /* __INTERSECTION_REFINE__ */
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}
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#endif /* __BVH_LOCAL__ */
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/* Ray intersection. We simply compute the vertex positions at the given ray
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* time and do a ray intersection with the resulting triangle.
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*/
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ccl_device_inline bool motion_triangle_intersect(
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KernelGlobals *kg,
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Intersection *isect,
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float3 P,
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float3 dir,
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float time,
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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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/* Primitive index for vertex location lookup. */
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int prim = kernel_tex_fetch(__prim_index, prim_addr);
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int fobject = (object == OBJECT_NONE)
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? kernel_tex_fetch(__prim_object, prim_addr)
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: object;
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/* Get vertex locations for intersection. */
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float3 verts[3];
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motion_triangle_vertices(kg, fobject, prim, time, verts);
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/* Ray-triangle intersection, unoptimized. */
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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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verts[0], verts[1], verts[2],
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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->t = t;
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isect->u = u;
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isect->v = v;
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isect->prim = prim_addr;
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isect->object = object;
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isect->type = PRIMITIVE_MOTION_TRIANGLE;
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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 intersections. 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 motion_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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float time,
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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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/* Primitive index for vertex location lookup. */
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int prim = kernel_tex_fetch(__prim_index, prim_addr);
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/* Get vertex locations for intersection. */
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float3 verts[3];
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motion_triangle_vertices(kg, local_object, prim, time, verts);
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/* Ray-triangle intersection, unoptimized. */
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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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verts[0], verts[1], verts[2],
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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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*/
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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->t = t;
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isect->u = u;
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isect->v = v;
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isect->prim = prim_addr;
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isect->object = object;
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isect->type = PRIMITIVE_MOTION_TRIANGLE;
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/* Record geometric normal. */
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local_isect->Ng[hit] = normalize(cross(verts[1] - verts[0],
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verts[2] - verts[0]));
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}
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#endif /* __BVH_LOCAL__ */
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CCL_NAMESPACE_END
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