# LYGIA Shader Library

## orenNayar (`lygia`/`lighting`/`diffuse`/`orenNayar`)

Calculate diffuse contribution using Oren and Nayar equation https://en.wikipedia.org/wiki/Oren%E2%80%93Nayar_reflectance_model

Use:

``````<float> diffuseOrenNayar(<vec3> light, <vec3> normal, <vec3> view, <float> roughness)
``````
``````<float> diffuseOrenNayar(<vec3> L, <vec3> N, <vec3> V, <float> NoV, <float> NoL, <float> roughness)
``````

Check it on Github

``````
#ifndef FNC_DIFFUSE_ORENNAYAR
#define FNC_DIFFUSE_ORENNAYAR

float diffuseOrenNayar(const in vec3 L, const in vec3 N, const in vec3 V, const in float NoV, const in float NoL, const in float roughness) {
float LoV = dot(L, V);

float s = LoV - NoL * NoV;
float t = mix(1.0, max(NoL, NoV), step(0.0, s));

float sigma2 = roughness * roughness;
float A = 1.0 + sigma2 * (1.0 / (sigma2 + 0.13) + 0.5 / (sigma2 + 0.33));
float B = 0.45 * sigma2 / (sigma2 + 0.09);

return max(0.0, NoL) * (A + B * s / t);
}

float diffuseOrenNayar(const in vec3 L, const in vec3 N, const in vec3 V, const in float roughness) {
float NoV = max(dot(N, V), 0.001);
float NoL = max(dot(N, L), 0.001);
return diffuseOrenNayar(L, N, V, NoV, NoL, roughness);
}

#endif
``````

Use:

``````<float> diffuseOrenNayar(<float3> light, <float3> normal, <float3> view, <float> roughness )
``````
``````<float> diffuseOrenNayar(<float3> L, <float3> N, <float3> V, <float> NoV, <float> NoL, <float> roughness)
``````

Check it on Github

``````
#ifndef FNC_DIFFUSE_ORENNAYAR
#define FNC_DIFFUSE_ORENNAYAR

float diffuseOrenNayar(float3 L, float3 N, float3 V, float NoV, float NoL, float roughness) {
float LoV = dot(L, V);

float s = LoV - NoL * NoV;
float t = lerp(1.0, max(NoL, NoV), step(0.0, s));

float sigma2 = roughness * roughness;
float A = 1.0 + sigma2 * (1.0 / (sigma2 + 0.13) + 0.5 / (sigma2 + 0.33));
float B = 0.45 * sigma2 / (sigma2 + 0.09);

return max(0.0, NoL) * (A + B * s / t);
}

float diffuseOrenNayar(float3 L, float3 N, float3 V, float roughness) {
float NoV = max(dot(N, V), 0.001);
float NoL = max(dot(N, L), 0.001);
return diffuseOrenNayar(L, N, V, NoV, NoL, roughness);
}

#endif
``````

Check it on Github

``````
fn diffuseOrenNayar(L: vec3f, N: vec3f, V: vec3f, NoV: f32, NoL: f32, roughness: f32) -> f32{
let LoV = dot(L, V);

let s = LoV - NoL * NoV;
let t = mix(1.0, max(NoL, NoV), step(0.0, s));

let sigma2 = roughness * roughness;
let A = 1.0 + sigma2 * (1.0 / (sigma2 + 0.13) + 0.5 / (sigma2 + 0.33));
let B = 0.45 * sigma2 / (sigma2 + 0.09);

return max(0.0, NoL) * (A + B * s / t);
}
``````