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#version 330 core
in vert_t {
vec3 position;
vec3 normal;
} vert;
out vec4 frag_color;
uniform vec3 camera;
uniform vec3 color;
uniform float metallic;
uniform float roughness;
uniform float ao;
struct light_t {
vec3 position;
vec3 color;
};
const int light_count = 4;
uniform light_t lights[light_count];
const float PI = 3.14159265358;
vec3 fresnel_shlick(float costheta, vec3 f0)
{
return f0 + (1.0 - f0) * pow(1.0 - costheta, 5.0);
}
float distribution_ggx(vec3 n, vec3 h, float roughness)
{
float a = roughness * roughness;
float a2 = a * a;
float ndoth = max(dot(n, h), 0.0);
float ndoth2 = ndoth * ndoth;
float num = a2;
float denom = (ndoth2 * (a2 - 1.0) + 1.0);
denom = PI * denom * denom;
return num / denom;
}
float geometry_shlick_ggx(float ndotv, float roughness)
{
float r = roughness + 1.0;
float k = r * r / 8.0;
float num = ndotv;
float denom = ndotv * (1.0 - k) + k;
return num / denom;
}
float geometry_smith(vec3 n, vec3 v, vec3 l, float roughness)
{
float ndotv = max(dot(n, v), 0.0);
float ndotl = max(dot(n, l), 0.0);
float ggx2 = geometry_shlick_ggx(ndotv, roughness);
float ggx1 = geometry_shlick_ggx(ndotl, roughness);
return ggx1 * ggx2;
}
void main(void)
{
vec3 n = vert.normal;
vec3 v = normalize(camera - vert.position);
vec3 lo = vec3(0.0);
for (int i = 0; i < light_count; i++) {
vec3 l = normalize(lights[i].position - vert.position);
vec3 h = normalize(v + l);
float ndotv = max(dot(n, v), 0.0);
float ndotl = max(dot(n, l), 0.0);
float distance = length(lights[i].position - vert.position);
float attenuation = 1.0 / (distance * distance);
vec3 radiance = lights[i].color * attenuation;
vec3 f0 = vec3(0.04);
f0 = mix(f0, color, metallic);
vec3 f = fresnel_shlick(max(dot(h, v), 0.0), f0);
float ndf = distribution_ggx(n, h, roughness);
float g = geometry_smith(n, v, l, roughness);
vec3 numerator = ndf * g * f;
float denominator = 4.0 * ndotv * ndotl;
vec3 specular = numerator / max(denominator, 0.001);
vec3 ks = f;
vec3 kd = vec3(1.0) - ks;
kd *= 1.0 - metallic;
lo += (kd * color / PI + specular) * radiance * ndotl;
}
vec3 ambient = vec3(0.03) * color * ao;
frag_color = vec4(ambient + lo, 1.0);
}
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