struct Material {
    p0: vec2<f32>,
    c0: vec2<f32>,
    c1: vec2<f32>,
    p1: vec2<f32>,
    width: f32,
    color: vec4<f32>,
};

@group(2) @binding(0)
var<uniform> mat: Material;

fn bezier(p0: vec2<f32>, c0: vec2<f32>, c1: vec2<f32>, p1: vec2<f32>, t: f32) -> vec2<f32> {
    let u = 1.0 - t;
    return
        u*u*u*p0 +
        3.0*u*u*t*c0 +
        3.0*u*t*t*c1 +
        t*t*t*p1;
}

fn distance_to_bezier(p: vec2<f32>) -> f32 {
    var min_d = 1e9;
    let steps = 32;

    var prev = mat.p0;
    for (var i = 1; i <= steps; i++) {
        let t = f32(i) / f32(steps);
        let cur = bezier(mat.p0, mat.c0, mat.c1, mat.p1, t);

        // distance to segment
        let v = cur - prev;
        let w = p - prev;
        let t_seg = clamp(dot(w, v) / dot(v, v), 0.0, 1.0);
        let proj = prev + t_seg * v;

        min_d = min(min_d, distance(p, proj));
        prev = cur;
    }

    return min_d;
}

@fragment
fn fragment(
    @location(0) world_pos: vec3<f32>,
) -> @location(0) vec4<f32> {
    let d = distance_to_bezier(world_pos.xy);

    let half_w = mat.width * 0.5;
    let aa = fwidth(d);

    let alpha = smoothstep(half_w + aa, half_w - aa, d);

    if (alpha <= 0.001) {
        discard;
    }

    return vec4(mat.color.rgb, mat.color.a * alpha);
}