forked from bartvdbraak/blender
91 lines
2.7 KiB
C
91 lines
2.7 KiB
C
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/*
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* Copyright 2011, Blender Foundation.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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CCL_NAMESPACE_BEGIN
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/* See "Tracing Ray Differentials", Homan Igehy, 1999. */
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__device void differential_transfer(differential3 *dP_, const differential3 dP, float3 D, const differential3 dD, float3 Ng, float t)
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{
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/* ray differential transfer through homogenous medium, to
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* compute dPdx/dy at a shading point from the incoming ray */
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float3 tmp = D/dot(D, Ng);
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float3 tmpx = dP.dx + t*dD.dx;
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float3 tmpy = dP.dy + t*dD.dy;
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dP_->dx = tmpx - dot(tmpx, Ng)*tmp;
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dP_->dy = tmpy - dot(tmpy, Ng)*tmp;
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}
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__device void differential_incoming(differential3 *dI, const differential3 dD)
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{
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/* compute dIdx/dy at a shading point, we just need to negate the
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* differential of the ray direction */
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dI->dx = -dD.dx;
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dI->dy = -dD.dy;
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}
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__device void differential_dudv(differential *du, differential *dv, float3 dPdu, float3 dPdv, differential3 dP, float3 Ng)
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{
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/* now we have dPdx/dy from the ray differential transfer, and dPdu/dv
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* from the primitive, we can compute dudx/dy and dvdx/dy. these are
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* mainly used for differentials of arbitrary mesh attributes. */
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/* find most stable axis to project to 2D */
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float xn= fabsf(Ng.x);
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float yn= fabsf(Ng.y);
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float zn= fabsf(Ng.z);
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if(zn < xn || zn < yn) {
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if(yn < xn || yn < zn) {
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dPdu.x = dPdu.y;
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dPdv.x = dPdv.y;
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dP.dx.x = dP.dx.y;
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dP.dy.x = dP.dy.y;
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}
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dPdu.y = dPdu.z;
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dPdv.y = dPdv.z;
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dP.dx.y = dP.dx.z;
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dP.dy.y = dP.dy.z;
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}
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/* using Cramer's rule, we solve for dudx and dvdx in a 2x2 linear system,
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* and the same for dudy and dvdy. the denominator is the same for both
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* solutions, so we compute it only once.
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*
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* dP.dx = dPdu * dudx + dPdv * dvdx;
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* dP.dy = dPdu * dudy + dPdv * dvdy; */
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float det = (dPdu.x*dPdv.y - dPdv.x*dPdu.y);
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if(det != 0.0f)
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det = 1.0f/det;
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du->dx = (dP.dx.x*dPdv.y - dP.dx.y*dPdv.x)*det;
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dv->dx = (dP.dx.y*dPdu.x - dP.dx.x*dPdu.y)*det;
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du->dy = (dP.dy.x*dPdv.y - dP.dy.y*dPdv.x)*det;
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dv->dy = (dP.dy.y*dPdu.x - dP.dy.x*dPdu.y)*det;
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}
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CCL_NAMESPACE_END
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