environment prefiltering

gistfile1.glsl

float lambertNDF(vec3 normal, vec3 dir, float roughness){
    float exponent = getLambertExponent(roughness*PI*0.5);
    float lambert = max(0.0, dot(normal, dir));
    return pow(lambert, exponent);
}


float ggxNDF(vec3 normal, vec3 dir, float roughness){
    float a = roughness*roughness;
    float d = max(0.000001, dot(normal, dir));
    //float ggx = sqrt((1.0-d)/(1.0+(a*a-1.0)*d));
    float ggx = (a*a)/pow(1.0+(a*a-1.0)*d*d, 2.0);
    return ggx*d;
}

vec3 envLookup(vec3 normal){
    vec2 dir = normalize(normal.xz);
    vec2 texcoord = vec2(
        atan(-dir.x, -dir.y)/TAU+0.5,
        acos(normal.y)/PI
    );
    return texture2D(envmap, texcoord).rgb;
}

vec4 prefilter(float roughness, vec3 normal){
    vec4 accum = vec4(0.0);
    for(int i=0; i<numSamples; i++){
        vec3 dir = samples[i];
        dir *= step(0.0, dot(normal, dir))*2.0-1.0; // reflect sample dir to above the normal
        //float weight = lambertNDF(normal, dir, roughness);
        float weight = ggxNDF(normal, dir, roughness);
        vec3 color = envLookup(dir);
        accum += vec4(color*weight, weight);
    }   
    return accum;
}