#version 460

layout(triangles, invocations=1) in;
in vec4 fca[]; 
layout(triangle_strip, max_vertices=9) out;
out vec4 fcolor;
uniform mat4 mvp;

float getavg(int idx){
	return 
		(gl_in[0].gl_Position[idx] + 
		gl_in[1].gl_Position[idx] + 
		gl_in[2].gl_Position[idx])
		/ 3;
}

void make_triangle(vec4 v1, vec4 c1, vec4 v2, vec4 c2, vec4 v3, vec4 c3){
	// Apply MVP
	v1 = mvp * v1;
	v2 = mvp * v2;
	v3 = mvp * v3;

	vec3 av = v1.xyz - v3.xyz;
	vec3 bv = v2.xyz - v3.xyz;
	vec3 normal = normalize(cross(av,bv));
	vec3 light_direction = vec3(1, 0, 1);
	float light_factor = dot(light_direction, normal.xyz) * .8;
	if(light_factor < 0.3)
		light_factor = 0.3;
		
	gl_Position = v1;
	fcolor = c1 * light_factor;
	EmitVertex();
	gl_Position = v2;
	fcolor = c2 * light_factor;
	EmitVertex();
	gl_Position = v3;
	fcolor = c3 * light_factor;
	EmitVertex();
	EndPrimitive();

}

void main(void) {

	if(gl_InvocationID == 1){
		make_triangle(
			gl_in[0].gl_Position, vec4(0, .6, .6, 1),
			gl_in[1].gl_Position, vec4(0, .6, .6, 1),
			gl_in[2].gl_Position, vec4(0, .6, .6, 1));
	}
	else {
		vec3 av = gl_in[2].gl_Position.xyz - gl_in[0].gl_Position.xyz;
		vec3 bv = gl_in[1].gl_Position.xyz - gl_in[0].gl_Position.xyz;
		vec4 normal = -vec4(normalize(cross(av,bv)), 0);
		normal *= -.999;
		vec3 light_direction = vec3(1, 0, 0);
		float light_factor = dot(light_direction, normal.xyz);
		if(light_factor < 0.1)
			light_factor = 0.1;
		
	
		vec4 center = vec4(getavg(0), getavg(1), getavg(2), 1);
		float d_01 = distance(gl_in[0].gl_Position, gl_in[1].gl_Position);
		float d_12 = distance(gl_in[1].gl_Position, gl_in[2].gl_Position);
		float d_20 = distance(gl_in[2].gl_Position, gl_in[0].gl_Position);
		bool t01 = true;
		bool t12 = true;
		bool t20 = true;
		if(d_01 > d_12 && d_01 > d_20){
			center = (gl_in[0].gl_Position + gl_in[1].gl_Position) / 2;
			t01 = false;
		}
		else if(d_12 > d_20){
			center = (gl_in[1].gl_Position + gl_in[2].gl_Position) / 2;
			t12 = false;
		}
		else {
			center = (gl_in[2].gl_Position + gl_in[0].gl_Position) / 2;
			t20 = false;
		}

		vec4 top = center + normal;
		if(t01)
			make_triangle(
				gl_in[0].gl_Position, fca[0],
				gl_in[1].gl_Position, fca[1],
				top, vec4(1, 1, 1, 1));
		if(t12)
			make_triangle(
				gl_in[1].gl_Position, fca[1],
				gl_in[2].gl_Position, fca[2],
				top, vec4(1, 1, 1, 1));
		if(t20)
			make_triangle(
					gl_in[2].gl_Position, fca[2],
				gl_in[0].gl_Position, fca[0],
				top, vec4(1, 1, 1, 1));
	}
	
}