diff options
| -rw-r--r-- | drivers/gles3/shaders/scene.glsl | 77 |
1 files changed, 59 insertions, 18 deletions
diff --git a/drivers/gles3/shaders/scene.glsl b/drivers/gles3/shaders/scene.glsl index 341a5bf2c7..b322a4c957 100644 --- a/drivers/gles3/shaders/scene.glsl +++ b/drivers/gles3/shaders/scene.glsl @@ -865,11 +865,57 @@ float contact_shadow_compute(vec3 pos, vec3 dir, float max_distance) { #endif -// GGX Specular -// Source: http://www.filmicworlds.com/images/ggx-opt/optimized-ggx.hlsl -float G1V(float dotNV, float k) -{ - return 1.0 / (dotNV * (1.0 - k) + k); + +// This returns the G_GGX function divided by 2 cos_theta_m, where in practice cos_theta_m is either N.L or N.V. +// We're dividing this factor off because the overall term we'll end up looks like +// (see, for example, the first unnumbered equation in B. Burley, "Physically Based Shading at Disney", SIGGRAPH 2012): +// +// F(L.V) D(N.H) G(N.L) G(N.V) / (4 N.L N.V) +// +// We're basically regouping this as +// +// F(L.V) D(N.H) [G(N.L)/(2 N.L)] [G(N.V) / (2 N.V)] +// +// and thus, this function implements the [G(N.m)/(2 N.m)] part with m = L or V. +// +// The contents of the D and G (G1) functions (GGX) are taken from +// E. Heitz, "Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs", J. Comp. Graph. Tech. 3 (2) (2014). +// Eqns 71-72 and 85-86 (see also Eqns 43 and 80). + +float G_GGX_2cos(float cos_theta_m, float alpha) { + // Schlick's approximation + // C. Schlick, "An Inexpensive BRDF Model for Physically-based Rendering", Computer Graphics Forum. 13 (3): 233 (1994) + // Eq. (19), although see Heitz (2014) the about the problems with his derivation. + // It nevertheless approximates GGX well with k = alpha/2. + float k = 0.5*alpha; + return 0.5 / (cos_theta_m * (1.0 - k) + k); + + // float cos2 = cos_theta_m*cos_theta_m; + // float sin2 = (1.0-cos2); + // return 1.0 /( cos_theta_m + sqrt(cos2 + alpha*alpha*sin2) ); +} + +float D_GXX(float cos_theta_m, float alpha) { + float alpha2 = alpha*alpha; + float d = 1.0 + (alpha2-1.0)*cos_theta_m*cos_theta_m; + return alpha2/(M_PI * d * d); +} + +float G_GGX_anisotropic_2cos(float cos_theta_m, float alpha_x, float alpha_y, float cos_phi, float sin_phi) { + float cos2 = cos_theta_m * cos_theta_m; + float sin2 = (1.0-cos2); + float s_x = alpha_x * cos_phi; + float s_y = alpha_y * sin_phi; + return 1.0 / (cos_theta_m + sqrt(cos2 + (s_x*s_x + s_y*s_y)*sin2 )); +} + +float D_GXX_anisotropic(float cos_theta_m, float alpha_x, float alpha_y, float cos_phi, float sin_phi) { + float cos2 = cos_theta_m * cos_theta_m; + float sin2 = (1.0-cos2); + float r_x = cos_phi/alpha_x; + float r_y = sin_phi/alpha_y; + float d = cos2 + sin2*(r_x * r_x + r_y * r_y); + return 1.0 / (M_PI * alpha_x * alpha_y * d * d ); } @@ -1019,7 +1065,6 @@ LIGHT_SHADER_CODE #elif defined(SPECULAR_SCHLICK_GGX) // shlick+ggx as default - float alpha = roughness * roughness; vec3 H = normalize(V + L); @@ -1035,26 +1080,22 @@ LIGHT_SHADER_CODE float ay = ry*ry; float XdotH = dot( T, H ); float YdotH = dot( B, H ); - float denom = XdotH*XdotH / (ax*ax) + YdotH*YdotH / (ay*ay) + cNdotH*cNdotH; - float D = 1.0 / ( M_PI * ax*ay * denom*denom ); + float D = D_GXX_anisotropic(cNdotH, ax, ay, XdotH, YdotH); + float G = G_GGX_anisotropic_2cos(cNdotL, ax, ay, XdotH, YdotH) * G_GGX_anisotropic_2cos(cNdotV, ax, ay, XdotH, YdotH); #else - float alphaSqr = alpha * alpha; - float denom = cNdotH * cNdotH * (alphaSqr - 1.0) + 1.0; - float D = alphaSqr / (M_PI * denom * denom); + float alpha = roughness * roughness; + float D = D_GGX(cNdotH, alpha); + float G = G_GGX_2cos(cNdotL, alpha) * G_GGX_2cos(cNdotV, alpha); #endif // F float F0 = 1.0; // FIXME float cLdotH5 = SchlickFresnel(cLdotH); float F = mix(cLdotH5, 1.0, F0); - // V - float k = alpha / 2.0f; - float vis = G1V(cNdotL, k) * G1V(cNdotV, k); - - float speci = cNdotL * D * F * vis; + float specular_brdf_NL = cNdotL * D * F * G; - specular_light += speci * light_color * specular_blob_intensity * attenuation; + specular_light += specular_brdf_NL * light_color * specular_blob_intensity * attenuation; #endif #if defined(LIGHT_USE_CLEARCOAT) @@ -1069,7 +1110,7 @@ LIGHT_SHADER_CODE #endif float Dr = GTR1(cNdotH, mix(.1, .001, clearcoat_gloss)); float Fr = mix(.04, 1.0, cLdotH5); - float Gr = G1V(cNdotL, .25) * G1V(cNdotV, .25); + float Gr = G_GGX_2cos(cNdotL, .25) * G_GGX_2cos(cNdotV, .25); specular_light += .25*clearcoat*Gr*Fr*Dr; |