// Mipmap generation: each level is a bilinear 2×2 average of the one above.

@group(0) @binding(0) var src: texture_2d<f32>;
@group(0) @binding(1) var samp: sampler;

struct VOut {
    @builtin(position) pos: vec4<f32>,
    @location(0) uv: vec2<f32>,
};

@vertex
fn vs(@builtin(vertex_index) i: u32) -> VOut {
    // One oversized triangle covering the target.
    let uv = vec2(f32((i << 1u) & 2u), f32(i & 2u));
    var out: VOut;
    out.pos = vec4(uv.x * 2.0 - 1.0, 1.0 - uv.y * 2.0, 0.0, 1.0);
    out.uv = uv;
    return out;
}

@fragment
fn fs(in: VOut) -> @location(0) vec4<f32> {
    return textureSample(src, samp, in.uv);
}