SuperTuxKart 1.5 upstream source (from official release tarball)

data/shaders/ge_shaders/utils/pbr_utils.glsl

@@ -0,0 +1,91 @@
+vec2 F_AB(float perceptual_roughness, float NdotV)
+{
+    vec4 c0 = vec4(-1.0, -0.0275, -0.572, 0.022);
+    vec4 c1 = vec4(1.0, 0.0425, 1.04, -0.04);
+    vec4 r = perceptual_roughness * c0 + c1;
+    float a004 = min(r.x * r.x, pow(2.0, -9.28 * NdotV)) * r.x + r.y;
+    return vec2(-1.04, 1.04) * a004 + r.zw;
+}
+
+// Lambert model
+float F_Schlick(float f0, float f90, float VdotH)
+{
+    return mix(f0, f90, pow(1.0 - VdotH, 5.0));
+}
+
+float Fd_Burley(float roughness, float NdotV, float NdotL, float LdotH)
+{
+    // Don't divide by Pi to avoid light being too dim.
+    float f90 = 0.5 + 2.0 * roughness * LdotH * LdotH;
+    float lightScatter = F_Schlick(1.0, f90, NdotL);
+    float viewScatter = F_Schlick(1.0, f90, NdotV);
+    return lightScatter * viewScatter;
+}
+
+// Calculate distribution.
+// Based on https://google.github.io/filament/Filament.html#citation-walter07
+// D_GGX(h,α) = α^2 / { π ((n⋅h)^2 (α2−1) + 1)^2 }
+// Simple implementation, has precision problems when using fp16 instead of fp32
+// see https://google.github.io/filament/Filament.html#listing_speculardfp16
+float D_GGX(float roughness, float NdotH)
+{
+    float oneMinusNdotHSquared = 1.0 - NdotH * NdotH;
+    float a = NdotH * roughness;
+    float k = roughness / (oneMinusNdotHSquared + a * a);
+    return k * k * (1.0 / 3.14159265359);
+}
+
+// Calculate visibility.
+// Hammon 2017, "PBR Diffuse Lighting for GGX+Smith Microsurfaces"
+// see https://google.github.io/filament/Filament.html#listing_approximatedspecularv
+float V_Smith_GGX_Correlated(float roughness, float NdotV, float NdotL)
+{
+    return 0.5 / mix(2.0 * NdotL * NdotV, NdotL + NdotV, roughness);
+}
+
+// Fresnel function
+// see https://google.github.io/filament/Filament.html#citation-schlick94
+// F_Schlick(v,h,f_0,f_90) = f_0 + (f_90 − f_0) (1 − v⋅h)^5
+vec3 fresnel(vec3 f0, float f90, float VdotH)
+{
+    return f0 + (f90 - f0) * pow(1.0 - VdotH, 5.0);
+}
+
+vec3 envBRDFApprox(vec3 F0, vec2 F_ab)
+{
+    return F0 * F_ab.x + F_ab.y;
+}
+
+float perceptualRoughnessToRoughness(float perceptual_roughness)
+{
+    float roughness = clamp(perceptual_roughness, 0.089, 1.0);
+    return roughness * roughness;
+}
+
+vec3 environmentLight(
+    vec3 irradiance,
+    vec3 radiance,
+    float roughness,
+    vec3 diffuse_color,
+    vec2 F_ab,
+    vec3 F0,
+    float F90,
+    float NdotV)
+{
+    // Multiscattering approximation: https://www.jcgt.org/published/0008/01/03/paper.pdf
+    // Useful reference: https://bruop.github.io/ibl
+    vec3 Fr = max(vec3(1.0 - roughness), F0) - F0;
+    vec3 kS = F0 + Fr * pow(1.0 - NdotV, 5.0);
+    float Ess = F_ab.x + F_ab.y;
+    vec3 FssEss = kS * Ess * F90;
+    float Ems = 1.0 - Ess;
+    vec3 Favg = F0 + (1.0 - F0) / 21.0;
+    vec3 Fms = FssEss * Favg / (1.0 - Ems * Favg);
+    vec3 FmsEms = Fms * Ems;
+    vec3 Edss = 1.0 - (FssEss + FmsEms);
+    vec3 kD = diffuse_color * Edss;
+
+    vec3 diffuse = (FmsEms + kD) * irradiance;
+    vec3 specular = FssEss * radiance;
+    return diffuse + specular;
+}