53 lines
1.6 KiB
Forth
53 lines
1.6 KiB
Forth
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/*
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Copyright (c) 2013 yvt
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This file is part of OpenSpades.
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OpenSpades is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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OpenSpades 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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You should have received a copy of the GNU General Public License
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along with OpenSpades. If not, see <http://www.gnu.org/licenses/>.
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*/
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// http://en.wikipedia.org/wiki/Oren–Nayar_reflectance_model
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float OrenNayar(float sigma, float dotLight, float dotEye) {
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if(dotLight < 0.)
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return 0.;
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float sigma2 = sigma * sigma;
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float A = 1. - 0.5 * sigma2 / (sigma2 + 0.33);
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float B = 0.45 * sigma2 / (sigma2 + 0.09);
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float scale = 1. / A;
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float scaledB = B * scale;
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vec2 dotLightEye = vec2(dotLight, dotEye);
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vec2 sinLightEye = sqrt(1. - dotLightEye * dotLightEye);
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float alphaSin = max(sinLightEye.x, sinLightEye.y);
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float betaCos = max(dotLight, dotEye);
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// (tan x)^2 + 1 = 1 / (cosx)^2
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// tan x = sqrt(1 / (cosx)^2 - 1)
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float betaCos2 = betaCos * betaCos;
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// rsq optimization; 1/x-1 = (1-x)/x
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float betaTan = 1. / sqrt(betaCos2 / (1. - betaCos2)); //sqrt(1. / betaCos2 - 1.);
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// cos(dotLight - dotEye)
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vec4 vecs = vec4(dotLightEye, sinLightEye);
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float diffCos = dot(vecs.xz, vecs.yw);
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// compute
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return dotLight * (1. + scaledB * diffCos * alphaSin * betaTan);
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}
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