struct Uniforms {
    screen_size: vec2f,
    cursor_pos: vec2f,
    // Outer rounded rect: inset from screen edge
    outer_inset: f32,
    outer_corner_radius: f32,
    // Inner rounded rect: inset further by ring_width
    ring_width: f32,
    inner_corner_radius: f32,
    // Glow
    glow_spread: f32,
    // Cursor avoidance
    cursor_avoid_radius: f32,
    cursor_avoid_falloff: f32,
    // Color temperature (linear RGB)
    _pad: f32,
    color: vec3f,
    _pad2: f32,
}

@group(0) @binding(0) var<uniform> u: Uniforms;

@vertex
fn vs_main(@builtin(vertex_index) i: u32) -> @builtin(position) vec4f {
    let x = f32(i32(i) / 2) * 4.0 - 1.0;
    let y = f32(i32(i) % 2) * 4.0 - 1.0;
    return vec4f(x, y, 0.0, 1.0);
}

// Rounded rectangle SDF (Inigo Quilez).
fn rounded_rect_sdf(p: vec2f, h: vec2f, r: f32) -> f32 {
    let q = abs(p) - h + vec2f(r);
    return length(max(q, vec2f(0.0))) + min(max(q.x, q.y), 0.0) - r;
}

@fragment
fn fs_main(@builtin(position) pos: vec4f) -> @location(0) vec4f {
    let center = u.screen_size / 2.0;
    let p = pos.xy - center;

    // Outer rounded rect
    let outer_half = center - vec2f(u.outer_inset);
    let sd_outer = rounded_rect_sdf(p, outer_half, u.outer_corner_radius);

    // Inner rounded rect
    let inner_half = outer_half - vec2f(u.ring_width);
    let sd_inner = rounded_rect_sdf(p, inner_half, u.inner_corner_radius);

    // Ring: inside outer AND outside inner = solid at full brightness
    var alpha: f32;
    if sd_outer <= 0.0 && sd_inner >= 0.0 {
        alpha = 1.0;
    } else if sd_outer > 0.0 {
        // Gaussian glow fading outward
        let t = sd_outer / u.glow_spread;
        alpha = exp(-3.0 * t * t);
    } else {
        // Gaussian glow fading inward
        let t = -sd_inner / u.glow_spread;
        alpha = exp(-3.0 * t * t);
    }

    // Cursor avoidance — rounded square (box SDF with corner rounding)
    let cursor_half = vec2f(u.cursor_avoid_radius);
    let cursor_corner = u.cursor_avoid_radius * 0.3; // 30% rounding smooths the diagonals
    let cursor_sd = rounded_rect_sdf(pos.xy - u.cursor_pos, cursor_half, cursor_corner);
    if cursor_sd < u.cursor_avoid_falloff {
        let t_avoid = clamp(cursor_sd / u.cursor_avoid_falloff, 0.0, 1.0);
        alpha *= t_avoid * t_avoid * (3.0 - 2.0 * t_avoid);
    }

    // Premultiplied color output
    let rgb = u.color * alpha;
    return vec4f(rgb, alpha);
}