#ifdef DESC
[program]
type: graphics
vertex: main
fragment: main

[binding]
name: mesh
rate: vertex
[attribute]
name: position
type: vec3
[attribute]
name: normal
type: vec3
[attribute]
name: tangent
type: vec3
[attribute]
name: uv
type: vec2

[interpolator]
name: uv
type: vec2
[interpolator]
name: position
type: vec4
[interpolator]
name: tbn
type: mat3

[struct]
name: MVP
[variable]
name: model
type: mat4
[variable]
name: view_projection
type: mat4

[struct]
name: Material
[variable]
name: albedo
type: vec3
[variable]
name: metalness
type: float
[variable]
name: roughness
type: float
[variable]
name: ao
type: float
[variable]
name: camera_pos
type: vec3

[cbuffer]
name: c_mvp
type: MVP
stage: vertex

[cbuffer]
name: material
type: Material
stage: fragment

[texture]
name: albedo
stage: fragment
dimension: 2
[texture]
name: ao
stage: fragment
dimension: 2
[texture]
name: metal
stage: fragment
dimension: 2
[texture]
name: rough
stage: fragment
dimension: 2
[texture]
name: normal
stage: fragment
dimension: 2
[texture]
name: env_cube
stage: fragment
dimension: cube

[target]
name: colour
type: vec4

#endif

#ifdef VERTEX_SHADER

void main() {
	vec4 pos = c_mvp.model * vec4(position, 1.0);
	vec3 t = normalize((c_mvp.model * vec4(tangent, 0.0)).xyz);
	vec3 n = normalize((c_mvp.model * vec4(normal, 0.0)).xyz);
	vec3 b = cross(t, n);
	interpolator.tbn = mat3(t, b, n);
	interpolator.uv = uv;
	interpolator.position = pos;
	interpolator.tbn = mat3(t, b, n);
	gl_Position = c_mvp.view_projection * pos;
}

#endif

#ifdef FRAGMENT_SHADER

#define pi 3.14159265358979323846

vec3 diffuse_brdf(vec2 uv) {
	vec3 a = material.albedo * texture(albedo, uv).rgb;
	return a / pi;
}

float specular_G1(float a, vec3 v, vec3 n) {
	float ndv = max(dot(n, v), 0.0);
	float a1 = a + 1.0;
	float k = (a1 * a1) / 8.0;
	return ndv / (ndv * (1.0 - k) + k);
}

float specular_brdf(vec2 uv, vec3 ref, vec3 l, vec3 v, vec3 n) {
	float ndl = max(dot(n, l), 0.0);
	float ndv = max(dot(n, v), 0.0);
	float a = texture(rough, uv).r * material.roughness;
	float a2 = a * a;
	float ndr = max(dot(n, ref), 0.0);
	float b = ((ndr * ndr) * (a2 - 1) + 1);
	float D =
		a2 / (pi * b * b);
	float G = specular_G1(a, l, n) * specular_G1(a, v, n);
	float F0 = 0.04;
	float F = F0 + (1.0 - F0) *
		pow(2, ((-5.55473 * ndr - 6.98316), ndr));
	return (D * F * G) / (4.0 * ndl * ndv + 0.001);
}

void main() {
	vec2 uv = interpolator.uv;
	vec3 p = interpolator.position.xyz;

	vec3 nrmsample = texture(normal, uv).rgb;
	vec2 nrmxy = nrmsample.xy * 2.0 - 1.0;
	vec3 nrm = normalize(vec3(nrmxy, 1.0));
	if (nrmsample.b == 1.0) /* default texture */
		nrm = normalize(interpolator.tbn[2]);
	else
		nrm = normalize(interpolator.tbn * nrm);

	vec3 light_dir = vec3(0, 0, 1);
	vec3 col = texture(albedo, uv).rgb * material.albedo;
	float cos_theta_i = max(dot(nrm, light_dir), 0.0);
	vec3 view_dir = normalize(material.camera_pos - p);
	float met = texture(metal, uv).r * material.metalness;

	vec3 ref = reflect(-view_dir, nrm);
	vec3 spec_col = texture(env_cube, ref).rgb;
	vec3 amb_col = texture(env_cube, nrm).rgb;

	vec3 diffuse =
		diffuse_brdf(uv) *
		(1.0 - met) *
		cos_theta_i;
	vec3 spec =
		mix(spec_col, col, met) *
		specular_brdf(uv, ref, light_dir, view_dir, nrm) *
		cos_theta_i;
	vec3 ambient =
		min(amb_col, 0.05) *
		texture(ao, uv).r;

	colour = vec4(ambient + diffuse + spec, 1.0);
}

#endif