6e2f29b421
This keeps the behavior similar to the Disney BRDF, where 0.5 is neutral and lower/higher values respectively decrease/increase the dielectric specular. But it's more correct in that it's not an arbitrary scale on Fresnel, but rather adjusting the IOR. Ref #99447 Ref #112848 Pull Request: https://projects.blender.org/blender/blender/pulls/112552
51 lines
1.3 KiB
C
51 lines
1.3 KiB
C
/* SPDX-FileCopyrightText: 2009-2010 Sony Pictures Imageworks Inc., et al. All Rights Reserved.
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* SPDX-FileCopyrightText: 2011-2022 Blender Foundation
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*
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* SPDX-License-Identifier: BSD-3-Clause
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*
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* Adapted code from Open Shading Language. */
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float fresnel_dielectric_cos(float cosi, float eta)
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{
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/* compute fresnel reflectance without explicitly computing
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* the refracted direction */
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float c = fabs(cosi);
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float g = eta * eta - 1 + c * c;
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float result;
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if (g > 0) {
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g = sqrt(g);
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float A = (g - c) / (g + c);
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float B = (c * (g + c) - 1) / (c * (g - c) + 1);
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result = 0.5 * A * A * (1 + B * B);
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}
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else {
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result = 1.0; /* TIR (no refracted component) */
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}
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return result;
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}
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color fresnel_conductor(float cosi, color eta, color k)
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{
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color cosi2 = color(cosi * cosi);
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color one = color(1, 1, 1);
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color tmp_f = eta * eta + k * k;
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color tmp = tmp_f * cosi2;
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color Rparl2 = (tmp - (2.0 * eta * cosi) + one) / (tmp + (2.0 * eta * cosi) + one);
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color Rperp2 = (tmp_f - (2.0 * eta * cosi) + cosi2) / (tmp_f + (2.0 * eta * cosi) + cosi2);
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return (Rparl2 + Rperp2) * 0.5;
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}
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float F0_from_ior(float eta)
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{
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float f0 = (eta - 1.0) / (eta + 1.0);
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return f0 * f0;
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}
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float ior_from_F0(float f0)
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{
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float sqrt_f0 = sqrt(clamp(f0, 0.0, 0.99));
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return (1.0 + sqrt_f0) / (1.0 - sqrt_f0);
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}
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