#version 330 core

in vert_t {
    vec2 tex_coords;
} vert;

out vec4 frag_color;

uniform sampler2D positions;
uniform sampler2D normals;
uniform sampler2D color_specular;

uniform vec3 view_position;

struct light_t {
    vec3 position;
    vec3 color;
};

const int light_count = 200;
uniform light_t lights[light_count];

const float linear = 0.7f;
const float quadratic = 1.8f;

void main()
{
    vec3 position = texture(positions, vert.tex_coords).rgb;
    vec3 normal = texture(normals, vert.tex_coords).rgb;
    vec3 color = texture(color_specular, vert.tex_coords).rgb;
    float specular = texture(color_specular, vert.tex_coords).a;

    vec3 ambient = 0.1 * color;
    vec3 view_dir = normalize(view_position - position);
    vec3 result = ambient;
    for (int i = 0; i < light_count; i++) {
        vec3 light_dir = normalize(lights[i].position - position);
        vec3 diffuse = max(dot(normal, light_dir), 0.0) * color * lights[i].color;
        float distance = length(lights[i].position - position);
        float attenuation = 1.0 / (1.0 + linear * distance + quadratic * distance * distance);
        vec3 halfway_dir = normalize(view_dir + light_dir);
        vec3 specular = pow(max(dot(halfway_dir, normal), 0.0), 32.0) * vec3(0.5);
        result += (diffuse + specular) * attenuation;
    }
    frag_color = vec4(result, 1.0);
}