struct ray {
    vec3 origin;
    vec3 direction;
};

layout(set = 0, binding = 0) buffer Inputs {
    vec4 sky_color;
    vec4 ground_color;
    vec4 camera_pos;

    float viewport_width;
    float viewport_height;
    float proj_plane_distance;
    float padding;

    vec4 sphere_position;

    vec4 [1920 * 1080] image;
};

bool hit_sphere(vec3 position, float radius, ray r) {
    // Vector from the ray origin to sphere position
    vec3 origin_center = r.origin - position;

    float a = dot(r.direction, r.direction);
    float half_b = dot(r.direction, origin_center);
    float c = dot(origin_center, origin_center) - radius * radius;
    float discriminant = half_b * half_b - a * c;

    return (discriminant > 0);
}

void main() {
    uint x = gl_GlobalInvocationID.x;
    uint y = gl_GlobalInvocationID.y;
    uint width = gl_NumWorkGroups.x;
    uint height = gl_NumWorkGroups.y;

    vec2 uv = vec2(float(x) / (width - 1), float(y) / (height - 1));

    vec3 first = camera_pos.xyz - vec3(viewport_width / 2.0, viewport_height / 2.0, proj_plane_distance);
    vec3 proj_plane_pos = first + vec3(uv.x * viewport_width, uv.y * viewport_height, 0.0);

    ray r = ray(camera_pos.xyz, proj_plane_pos - camera_pos.xyz);
    if (hit_sphere(sphere_position.xyz, 0.5, r)) {
        image[y * width + x] = vec4(1.0, 0.0, 0.0, 0.0);
        return;
    }

    image[y * width + x] = mix(sky_color, ground_color, uv.y);
}