// Based on: https://github.com/frozein/VkGalaxy/blob/main/assets/shaders/particle.frag
#version 450

layout (location = 0) in vec2 in_tex;
layout (location = 1) in float temperature;
layout (location = 2) in flat uint in_type;

layout (location = 0) out vec4 out_color;

// Based on: https://github.com/zubetto/BlackBodyRadiation
vec4 blackbody(in float temp_in_kel)
{
    if(temp_in_kel <= 0.0)
    {
        return vec4(0.0, 0.0, 0.0, 1.0);
    }

    vec4 color = {0.0, 0.0, 0.0, 1.0};
    float kel = temp_in_kel * 500.0;

    float u = 0.000536332 * kel;
    color.r = 0.638749 + (u + 1.57533) / (u * u + 0.28664);

    u = 0.0019639 * kel;
    color.g = 0.971029 + (u - 10.8015) / (u * u + 6.59002);

    float p = 0.00668406 * kel + 23.3962;
    u = 0.000941064 * kel;
    float q = u * u + 0.00100641 * kel + 10.9068;
    color.b = 2.25398 - p / q;

    return color;
}

void main(void)
{
    vec2 centered_pos = 3.0 * (in_tex - 0.5);

    if (in_type == 0)  // Star
    {
        out_color = blackbody(temperature);
    }

    else if (in_type == 1) // Dust
    {
        out_color.rgb *= vec3(0.5, 0.5, 1.0);
        out_color.a *= max(1.0 - length(centered_pos), 0.0);
    }
    else // H-2 regions
    {
        float dist = max(1.0 - length(centered_pos), 0.0);

        out_color.rgb = mix(vec3(1.0, 0.0, 0.0), vec3(1.0), dist * dist * dist);
        out_color.a = dist * dist;
    }
}