#define RENDER_DIST 40.0
#define INTERSECT_DIST 0.01

float floorHeight = 0.0;
vec3 spherePos;
float sphereRadius = 7.0;

float distanceToScene(vec3 origin)
{
    float floor_dist = origin.y - floorHeight;
    float sphere_dist = distance(origin, spherePos) - sphereRadius;
    return min(floor_dist, sphere_dist);
}

vec3 normalToSurface(vec3 pos)
{
    vec2 e = vec2(0.01, 0);
    float pos_dist = distanceToScene(pos);
    // vec3 normal =
    return vec3(0, 0, 0);
}

float rayMarch(vec3 ray_origin, vec3 ray_direction)
{
    float origin_dist = 0.0;
    while (origin_dist < RENDER_DIST)
    {
        vec3 new_origin = ray_origin + origin_dist * ray_direction;
        float scene_dist = distanceToScene(new_origin);
        if (scene_dist < INTERSECT_DIST) return origin_dist;
        origin_dist += scene_dist;
    }
    return -1.0;
}

void mainImage(out vec4 fragColor, in vec2 fragCoord)
{
    vec3 camera = vec3(0.0, 2.0, 1.0);
    vec2 uv = (fragCoord - 0.5 * iResolution.xy) / iResolution.y;
    vec3 direction = normalize(vec3(uv.x, uv.y, 1.0));

    spherePos = vec3(0.0, sin(iTime) + 2.0, 25.0);

    float dist = rayMarch(camera, direction);
    if (dist > -1.0)
    {
        float colour = 1.0 - (dist / RENDER_DIST);
        fragColor = vec4(colour, colour, colour, 1);
    }
    else
    {
        fragColor = vec4(0, 0, 0, 1);
    }
}