struct Point {
	pos: vec3<f32>,
	_pad: f32,
};

struct BillboardAxis {
	vector : vec3<f32>,
	_pad   : f32,
};

struct VSOut {
	@builtin(position) Position : vec4<f32>,
	@location(0)       uv       : vec2<f32>,
	@location(1)       color    : vec3<f32>,
};

@group(0) @binding(0) var<storage, read> positions: array<Point>;

@group(0) @binding(1) var<storage, read> sortedIndices: array<u32>;   // New binding for sorted indices

@group(0) @binding(2) var<uniform> viewProjectionMatrix: mat4x4<f32>;

@group(0) @binding(3) var<uniform> cameraRight    : BillboardAxis;

@group(0) @binding(4) var<uniform> cameraUp       : BillboardAxis;

@vertex
fn vertexEntryPoint(
	@builtin(vertex_index) vertexIndex: u32,
	@builtin(instance_index) instanceIndex: u32,
	@location(0) quadOffset: vec2<f32>
) -> VSOut {

	var output: VSOut;

	// Use the sorted index to get the actual particle index
	let actualIndex = sortedIndices[instanceIndex];

	let point = positions[actualIndex];
	let center = point.pos;
	let radius = 0.03;

	let rightOffset = cameraRight.vector * quadOffset.x * radius;
	let upOffset    = cameraUp.vector    * quadOffset.y * radius;

	let worldPos = vec4<f32>(center + rightOffset + upOffset, 1.0);

	output.Position = viewProjectionMatrix * worldPos;
	output.uv       = quadOffset;
	output.color    = (center + vec3<f32>(1.0, 1.0, 1.0)) * 0.5;

	return output;
}

@fragment
fn fragmentEntryPoint(
	@location(0) uv: vec2<f32>,
	@location(1) color: vec3<f32>
) -> @location(0) vec4<f32> {

	let dist = length(uv);
	if (dist > 1.0) {
		discard;
	}

	let z = sqrt(1.0 - dist * dist);
	let normal = normalize(vec3<f32>(uv.x, uv.y, z));
	let light = normalize(vec3<f32>(1.0, 1.0, 1.0));

	let diffuse = max(dot(normal, light), 0.0);

	return vec4<f32>(color * diffuse, 1.0);
}
