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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 texelfetch_noise_tex(coord) texelFetch(utilTex, ivec3(ivec2(coord) % LUT_SIZE, 2.0), 0)
/* Return texture coordinates to sample Surface LUT */
vec2 lut_coords(float cosTheta, float roughness)
{
float theta = acos(cosTheta);
vec2 coords = vec2(roughness, theta / M_PI_2);
/* scale and bias coordinates, for correct filtered lookup */
return coords * (LUT_SIZE - 1.0) / LUT_SIZE + 0.5 / LUT_SIZE;
}
vec2 lut_coords_ltc(float cosTheta, float roughness)
{
vec2 coords = vec2(roughness, sqrt(1.0 - cosTheta));
/* scale and bias coordinates, for correct filtered lookup */
return coords * (LUT_SIZE - 1.0) / LUT_SIZE + 0.5 / LUT_SIZE;
}
float get_btdf_lut(float NV, float roughness, float ior)
{
const vec3 lut_scale_bias_texel_size = vec3((LUT_SIZE - 1.0), 0.5, 1.5) / LUT_SIZE;
vec3 coords;
/* Try to compensate for the low resolution and interpolation error. */
coords.x = (ior > 1.0) ? (0.9 + lut_scale_bias_texel_size.z) +
(0.1 - lut_scale_bias_texel_size.z) * f0_from_ior(ior) :
(0.9 + lut_scale_bias_texel_size.z) * ior * ior;
coords.y = 1.0 - saturate(NV);
coords.xy *= lut_scale_bias_texel_size.x;
coords.xy += lut_scale_bias_texel_size.y;
const float lut_lvl_ofs = 4.0; /* First texture lvl of roughness. */
const float lut_lvl_scale = 16.0; /* How many lvl of roughness in the lut. */
float mip = roughness * lut_lvl_scale;
float mip_floor = floor(mip);
coords.z = lut_lvl_ofs + mip_floor + 1.0;
float btdf_high = textureLod(utilTex, coords, 0.0).r;
coords.z -= 1.0;
float btdf_low = textureLod(utilTex, coords, 0.0).r;
float btdf = (ior == 1.0) ? 1.0 : mix(btdf_low, btdf_high, mip - coords.z);
return btdf;
}
/** \} */
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