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Cycles: Deduplicate geometric factor calculation in the Beckmann distribution

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Also, this fixes a numerical issue where A would be inf.
Since later G is set to 1 if A is larger than 1.6, the code now checks the reciprocal of A for being smaller than 1/1.6 - same effect, but no inf involved.
This commit is contained in:
Lukas Stockner
2016-07-16 20:44:28 +02:00
parent a40073ffcc
commit 5ba78d76d4
1 changed files with 39 additions and 40 deletions
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79
intern/cycles/kernel/closure/bsdf_microfacet.h
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@@ -615,6 +615,36 @@ ccl_device void bsdf_microfacet_beckmann_blur(ShaderClosure *sc, float roughness
sc->data1 = fmaxf(roughness, sc->data1); /* alpha_y */ sc->data1 = fmaxf(roughness, sc->data1); /* alpha_y */
} }
ccl_device_inline float bsdf_beckmann_G1(float alpha, float cos_n)
{
cos_n *= cos_n;
float invA = alpha * safe_sqrtf((1.0f - cos_n) / cos_n);
if(invA < 0.625f) {
return 1.0f;
}
float a = 1.0f / invA;
return ((2.181f*a + 3.535f)*a) / ((2.577f*a + 2.276f)*a + 1.0f);
}
ccl_device_inline float bsdf_beckmann_aniso_G1(float alpha_x, float alpha_y, float cos_n, float cos_phi, float sin_phi)
{
cos_n *= cos_n;
sin_phi *= sin_phi;
cos_phi *= cos_phi;
alpha_x *= alpha_x;
alpha_y *= alpha_y;
float alphaO2 = (cos_phi*alpha_x + sin_phi*alpha_y) / (cos_phi + sin_phi);
float invA = safe_sqrtf(alphaO2 * (1 - cos_n) / cos_n);
if(invA < 0.625f) {
return 1.0f;
}
float a = 1.0f / invA;
return ((2.181f*a + 3.535f)*a) / ((2.577f*a + 2.276f)*a + 1.0f);
}
ccl_device float3 bsdf_microfacet_beckmann_eval_reflect(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf) ccl_device float3 bsdf_microfacet_beckmann_eval_reflect(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{ {
float alpha_x = sc->data0; float alpha_x = sc->data0;
@@ -646,10 +676,8 @@ ccl_device float3 bsdf_microfacet_beckmann_eval_reflect(const ShaderClosure *sc,
D = expf(-tanThetaM2 / alpha2) / (M_PI_F * alpha2 * cosThetaM4); D = expf(-tanThetaM2 / alpha2) / (M_PI_F * alpha2 * cosThetaM4);
/* eq. 26, 27: now calculate G1(i,m) and G1(o,m) */ /* eq. 26, 27: now calculate G1(i,m) and G1(o,m) */
float ao = 1 / (alpha_x * safe_sqrtf((1 - cosNO * cosNO) / (cosNO * cosNO))); G1o = bsdf_beckmann_G1(alpha_x, cosNO);
float ai = 1 / (alpha_x * safe_sqrtf((1 - cosNI * cosNI) / (cosNI * cosNI))); G1i = bsdf_beckmann_G1(alpha_x, cosNI);
G1o = ao < 1.6f ? (3.535f * ao + 2.181f * ao * ao) / (1 + 2.276f * ao + 2.577f * ao * ao) : 1.0f;
G1i = ai < 1.6f ? (3.535f * ai + 2.181f * ai * ai) / (1 + 2.276f * ai + 2.577f * ai * ai) : 1.0f;
} }
else { else {
/* anisotropic */ /* anisotropic */
@@ -668,24 +696,8 @@ ccl_device float3 bsdf_microfacet_beckmann_eval_reflect(const ShaderClosure *sc,
D = expf(-slope_x*slope_x - slope_y*slope_y) / (M_PI_F * alpha2 * cosThetaM4); D = expf(-slope_x*slope_x - slope_y*slope_y) / (M_PI_F * alpha2 * cosThetaM4);
/* G1(i,m) and G1(o,m) */ /* G1(i,m) and G1(o,m) */
float tanThetaO2 = (1 - cosNO * cosNO) / (cosNO * cosNO); G1o = bsdf_beckmann_aniso_G1(alpha_x, alpha_y, cosNO, dot(I, X), dot(I, Y));
float cosPhiO = dot(I, X); G1i = bsdf_beckmann_aniso_G1(alpha_x, alpha_y, cosNI, dot(omega_in, X), dot(omega_in, Y));
float sinPhiO = dot(I, Y);
float alphaO2 = (cosPhiO*cosPhiO)*(alpha_x*alpha_x) + (sinPhiO*sinPhiO)*(alpha_y*alpha_y);
alphaO2 /= cosPhiO*cosPhiO + sinPhiO*sinPhiO;
float tanThetaI2 = (1 - cosNI * cosNI) / (cosNI * cosNI);
float cosPhiI = dot(omega_in, X);
float sinPhiI = dot(omega_in, Y);
float alphaI2 = (cosPhiI*cosPhiI)*(alpha_x*alpha_x) + (sinPhiI*sinPhiI)*(alpha_y*alpha_y);
alphaI2 /= cosPhiI*cosPhiI + sinPhiI*sinPhiI;
float ao = 1 / (safe_sqrtf(alphaO2 * tanThetaO2));
float ai = 1 / (safe_sqrtf(alphaI2 * tanThetaI2));
G1o = ao < 1.6f ? (3.535f * ao + 2.181f * ao * ao) / (1 + 2.276f * ao + 2.577f * ao * ao) : 1.0f;
G1i = ai < 1.6f ? (3.535f * ai + 2.181f * ai * ai) / (1 + 2.276f * ai + 2.577f * ai * ai) : 1.0f;
} }
float G = G1o * G1i; float G = G1o * G1i;
@@ -740,10 +752,8 @@ ccl_device float3 bsdf_microfacet_beckmann_eval_transmit(const ShaderClosure *sc
float D = expf(-tanThetaM2 / alpha2) / (M_PI_F * alpha2 * cosThetaM4); float D = expf(-tanThetaM2 / alpha2) / (M_PI_F * alpha2 * cosThetaM4);
/* eq. 26, 27: now calculate G1(i,m) and G1(o,m) */ /* eq. 26, 27: now calculate G1(i,m) and G1(o,m) */
float ao = 1 / (alpha_x * safe_sqrtf((1 - cosNO * cosNO) / (cosNO * cosNO))); float G1o = bsdf_beckmann_G1(alpha_x, cosNO);
float ai = 1 / (alpha_x * safe_sqrtf((1 - cosNI * cosNI) / (cosNI * cosNI))); float G1i = bsdf_beckmann_G1(alpha_x, cosNI);
float G1o = ao < 1.6f ? (3.535f * ao + 2.181f * ao * ao) / (1 + 2.276f * ao + 2.577f * ao * ao) : 1.0f;
float G1i = ai < 1.6f ? (3.535f * ai + 2.181f * ai * ai) / (1 + 2.276f * ai + 2.577f * ai * ai) : 1.0f;
float G = G1o * G1i; float G = G1o * G1i;
/* probability */ /* probability */
@@ -820,8 +830,7 @@ ccl_device int bsdf_microfacet_beckmann_sample(KernelGlobals *kg, const ShaderCl
float cosNI = dot(N, *omega_in); float cosNI = dot(N, *omega_in);
/* eq. 26, 27: now calculate G1(i,m) */ /* eq. 26, 27: now calculate G1(i,m) */
float ai = 1 / (alpha_x * safe_sqrtf((1 - cosNI * cosNI) / (cosNI * cosNI))); G1i = bsdf_beckmann_G1(alpha_x, cosNI);
G1i = ai < 1.6f ? (3.535f * ai + 2.181f * ai * ai) / (1 + 2.276f * ai + 2.577f * ai * ai) : 1.0f;
} }
else { else {
/* anisotropic distribution */ /* anisotropic distribution */
@@ -836,16 +845,7 @@ ccl_device int bsdf_microfacet_beckmann_sample(KernelGlobals *kg, const ShaderCl
D = expf(-slope_x*slope_x - slope_y*slope_y) / (M_PI_F * alpha2 * cosThetaM4); D = expf(-slope_x*slope_x - slope_y*slope_y) / (M_PI_F * alpha2 * cosThetaM4);
/* G1(i,m) */ /* G1(i,m) */
float cosNI = dot(N, *omega_in); G1i = bsdf_beckmann_aniso_G1(alpha_x, alpha_y, dot(*omega_in, N), dot(*omega_in, X), dot(*omega_in, Y));
float tanThetaI2 = (1 - cosNI * cosNI) / (cosNI * cosNI);
float cosPhiI = dot(*omega_in, X);
float sinPhiI = dot(*omega_in, Y);
float alphaI2 = (cosPhiI*cosPhiI)*(alpha_x*alpha_x) + (sinPhiI*sinPhiI)*(alpha_y*alpha_y);
alphaI2 /= cosPhiI*cosPhiI + sinPhiI*sinPhiI;
float ai = 1 / (safe_sqrtf(alphaI2 * tanThetaI2));
G1i = ai < 1.6f ? (3.535f * ai + 2.181f * ai * ai) / (1 + 2.276f * ai + 2.577f * ai * ai) : 1.0f;
} }
float G = G1o * G1i; float G = G1o * G1i;
@@ -906,8 +906,7 @@ ccl_device int bsdf_microfacet_beckmann_sample(KernelGlobals *kg, const ShaderCl
float cosNI = dot(N, *omega_in); float cosNI = dot(N, *omega_in);
/* eq. 26, 27: now calculate G1(i,m) */ /* eq. 26, 27: now calculate G1(i,m) */
float ai = 1 / (alpha_x * safe_sqrtf((1 - cosNI * cosNI) / (cosNI * cosNI))); float G1i = bsdf_beckmann_G1(alpha_x, cosNI);
float G1i = ai < 1.6f ? (3.535f * ai + 2.181f * ai * ai) / (1 + 2.276f * ai + 2.577f * ai * ai) : 1.0f;
float G = G1o * G1i; float G = G1o * G1i;
/* eq. 21 */ /* eq. 21 */