Metallic BRDF

phong_metal.glsl

float PhongBase(vec3 viewdir, vec3 lightdir, vec3 normal) {
	return max(-dot(viewdir, reflect(lightdir, normal)), 0.0);
}

// Analytic specular without ambient specular might look better like this.
float HalfPhongBase(vec3 viewdir, vec3 lightdir, vec3 normal) {
	return -dot(viewdir, reflect(lightdir, normal)) / 2 + 0.5;
}

// Something to approximate the longer tail
// and tigher highlight of metalic surfaces.
float MetallicPow(float x, float pwr) {
	pwr = (pwr * x) - (pwr + 1.0);
	return (-x / pwr);
}