struct Material {
    color_a: vec4<f32>,
    color_b: vec4<f32>,
    border_color: vec4<f32>,
    time: f32,
    speed: f32,
    border_size: f32,
};

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

@fragment
fn fragment(in: VertexOutput) -> @location(0) vec4<f32> {
    let uv = in.uv;

    // animate
    let x = uv.x + params.time * params.speed;
    let g = fract(x);

    let fill = mix(params.color_a, params.color_b, g);

    // borders
    let top = step(uv.y, params.border_size);
    let bottom = step(1.0 - params.border_size, uv.y);
    let border_mask = max(top, bottom);

    return mix(fill, params.border_color, border_mask);
}