$input tex_coord, world_pos

#include "bgfx_shader.sh"
#include "shaderlib.sh"

//layout(early_fragment_tests) in;

SAMPLER2D(texture_atlas_sampler, 0);

uniform vec4 u_cubes_compute_params;

// Ref: https://en.wikipedia.org/wiki/Blinn%E2%80%93Phong_reflection_model

const float lightPower = 40.0;

void main()
{

	// vec4 col = texture2D(texture_atlas_sampler, tex_coord);

	// // if(col.r + col.g + col.b == 0.0) discard; // playing with transparency


	// vec3 normal = normalize(cross(dFdy(world_pos), dFdx(world_pos))); // screen space surface normal
	// //col = vec4(normal, 1.0f);

	// const float ambient = 0.2;
	// const vec3 light_pos = vec3(-5.0, 5.0, -5.0);
	// const vec3 light_col = vec3(1.0, 1.0, 1.0);
	// vec3 light_dir = light_pos - world_pos;
	// float squared_distance = light_dir.x*light_dir.x + light_dir.y*light_dir.y + light_dir.z*light_dir.z;
	// light_dir = normalize(light_dir);

    // vec4 diffuse = vec4(max(dot(light_dir, normal), 0) * light_col, 1.0);
	// col = col * ambient + col * diffuse;

	// // Note: if gl_FrontFacing is making problems
	// //    => https://stackoverflow.com/questions/24375171/is-there-a-reliable-alternative-to-gl-frontfacing-in-a-fragment-shader
	// //if (gl_FrontFacing) {
	// //	col = vec4(1.0,0.0,0.0,1.0);
	// //}else{
	// //	col = vec4(0.0,1.0,0.0,1.0);
	// //}


	// Calc id_coords (in id_atlas, for id sampling)
	//  in [0;ID_SIZE], is basically int
	// id_coord = floor(id_coord);
	// id_coord = id_coord + 
	// TODO use modf and combine floor/fract
	// ! flooring may not be needed anyway
	// just sample id_atlas with tex_coord

// Texturing rework V2
const uint IA_WIDTH = 2*8; // id's per row
const uint IA_HEIGHT = 2*8; // id's per column
const float ID_STRIDE_X = 1.0f / IA_WIDTH;
const float ID_STRIDE_Y = 1.0f / IA_HEIGHT;

	// Calc tex_coords (in tex_atlas, for texture sampling)
	//  in [0;1] in local texture space
	tex_coord = tex_coord * vec2(IA_WIDTH, IA_HEIGHT);
	tex_coord = fract(tex_coord);

	// vec4 col;
	// if (tex_coord.x < 0.5)
	// {
	// 	col = vec4(1.0, 0.0, 0.0, 1.0);
	// }
	// else
	// {
	// 	col = vec4(0.0, 1.0, 0.0, 1.0);
	// }

	vec4 col = vec4(tex_coord, 0.0, 1.0);

	gl_FragColor = col;
}