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#pragma BLENDER_REQUIRE(bsdf_common_lib.glsl)
/* ---------------------------------------------------------------------- */
/** \name Utiltex
*
* Utiltex is a sampler2DArray that stores a number of useful small utilitary textures and lookup
* tables.
* \{ */
uniform sampler2DArray utilTex;
#define LUT_SIZE 64
#define LTC_MAT_LAYER 0
#define LTC_BRDF_LAYER 1
#define BRDF_LUT_LAYER 1
#define NOISE_LAYER 2
#define LTC_DISK_LAYER 3 /* UNUSED */
/* Layers 4 to 20 are for BTDF Lut. */
const float lut_btdf_layer_first = 4.0;
const float lut_btdf_layer_count = 16.0;
#define texelfetch_noise_tex(coord) \
texelFetch(utilTex, ivec3(ivec2(coord) % LUT_SIZE, NOISE_LAYER), 0)
/* Return texture coordinates to sample Surface LUT. */
vec2 lut_coords(float cos_theta, float roughness)
{
vec2 coords = vec2(roughness, sqrt(1.0 - cos_theta));
/* scale and bias coordinates, for correct filtered lookup */
return coords * (LUT_SIZE - 1.0) / LUT_SIZE + 0.5 / LUT_SIZE;
}
/* Returns the GGX split-sum precomputed in LUT. */
vec2 brdf_lut(float cos_theta, float roughness)
{
return textureLod(utilTex, vec3(lut_coords(cos_theta, roughness), BRDF_LUT_LAYER), 0.0).rg;
}
/* Return texture coordinates to sample Surface LUT. */
vec3 lut_coords_btdf(float cos_theta, float roughness, float ior)
{
/* ior is sin of critical angle. */
float critical_cos = sqrt(1.0 - ior * ior);
vec3 coords;
coords.x = sqr(ior);
coords.y = cos_theta;
coords.y -= critical_cos;
coords.y /= (coords.y > 0.0) ? (1.0 - critical_cos) : critical_cos;
coords.y = coords.y * 0.5 + 0.5;
coords.z = roughness;
coords = saturate(coords);
/* scale and bias coordinates, for correct filtered lookup */
coords.xy = coords.xy * (LUT_SIZE - 1.0) / LUT_SIZE + 0.5 / LUT_SIZE;
return coords;
}
/* Returns GGX BTDF in first component and fresnel in second. */
vec2 btdf_lut(float cos_theta, float roughness, float ior)
{
if (ior <= 1e-5) {
return vec2(0.0);
}
if (ior >= 1.0) {
vec2 split_sum = brdf_lut(cos_theta, roughness);
float f0 = f0_from_ior(ior);
/* Baked IOR for GGX BRDF. */
const float specular = 1.0;
const float eta_brdf = (2.0 / (1.0 - sqrt(0.08 * specular))) - 1.0;
/* Avoid harsh transition comming from ior == 1. */
float f90 = fast_sqrt(saturate(f0 / (f0_from_ior(eta_brdf) * 0.25)));
float fresnel = F_brdf_single_scatter(vec3(f0), vec3(f90), split_sum).r;
/* Setting the BTDF to one is not really important since it is only used for multiscatter
* and it's already quite close to ground truth. */
float btdf = 1.0;
return vec2(btdf, fresnel);
}
vec3 coords = lut_coords_btdf(cos_theta, roughness, ior);
float layer = coords.z * lut_btdf_layer_count;
float layer_floored = floor(layer);
coords.z = lut_btdf_layer_first + layer_floored;
vec2 btdf_low = textureLod(utilTex, coords, 0.0).rg;
coords.z += 1.0;
vec2 btdf_high = textureLod(utilTex, coords, 0.0).rg;
/* Manual trilinear interpolation. */
vec2 btdf = mix(btdf_low, btdf_high, layer - layer_floored);
return btdf;
}
/** \} */
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