struct Particle {
    pos: vec4<f32>,
    vel: vec4<f32>,
    rot: vec4<f32>,
    color: vec4<f32>,
};

struct Uniforms {
    audio_peak: f32,
    aspect_ratio: f32,
    time: f32,
    beat: f32,
};

@group(0) @binding(0) var<storage, read> particles: array<Particle>;
@group(0) @binding(1) var<uniform> uniforms: Uniforms;

struct VSOut {
    @builtin(position) pos: vec4<f32>,
    @location(0) color: vec4<f32>,
    @location(1) uv: vec2<f32>,
};

@vertex fn vs_main(@builtin(vertex_index) vi: u32, @builtin(instance_index) ii: u32) -> VSOut {
    let p = particles[ii];
    let size = 0.02 + p.pos.z * 0.01 + uniforms.audio_peak * 0.02;
    var offsets = array<vec2<f32>, 6>(
        vec2<f32>(-1, -1),
        vec2<f32>(1, -1),
        vec2<f32>(-1, 1),
        vec2<f32>(-1, 1),
        vec2<f32>(1, -1),
        vec2<f32>(1, 1)
    );
    let offset = offsets[vi];
    let c = cos(p.rot.x);
    let s = sin(p.rot.x);
    let rotated_offset = vec2<f32>(offset.x * c - offset.y * s, offset.x * s + offset.y * c);
    let pos = vec2<f32>(p.pos.x + rotated_offset.x * size / uniforms.aspect_ratio, p.pos.y + rotated_offset.y * size);

    // Fade based on lifetime (p.pos.w goes from 1.0 to 0.0)
    let lifetime_fade = p.pos.w;
    let color_with_fade = vec4<f32>(p.color.rgb * (0.5 + 0.5 * uniforms.audio_peak), p.color.a * lifetime_fade);

    return VSOut(vec4<f32>(pos, 0.0, 1.0), color_with_fade, offset);
}

@fragment fn fs_main(@location(0) color: vec4<f32>, @location(1) uv: vec2<f32>) -> @location(0) vec4<f32> {
    // Calculate distance from center for circular shape
    let dist = length(uv);

    // Smooth circular falloff (1.0 at center, 0.0 at edge)
    let circle_alpha = smoothstep(1.0, 0.5, dist);

    // Apply circular fade to alpha channel
    return vec4<f32>(color.rgb, color.a * circle_alpha);
}