// INCLUDE: global uniform header

struct InstanceInput {
	@location(2) position: vec2<f32>,
	@location(3) velocity: vec2<f32>,
	@location(4) angle: f32,
	@location(5) angvel: f32,
	@location(6) size: f32,
	@location(7) created: f32,
	@location(8) expires: f32,
	@location(9) fade: f32,
	@location(10) texture_index: vec2<u32>,
	@location(11) texture_fade: f32,
};

struct VertexInput {
	@location(0) position: vec3<f32>,
	@location(1) texture_coords: vec2<f32>,
}

struct VertexOutput {
	@builtin(position) position: vec4<f32>,
	@location(0) tween: f32,
	@location(1) fade: f32,
	@location(2) texture_index_a: u32,
	@location(3) texture_coords_a: vec2<f32>,
	@location(4) texture_index_b: u32,
	@location(5) texture_coords_b: vec2<f32>,
}


@group(0) @binding(0)
var texture_array: binding_array<texture_2d<f32>>;
@group(0) @binding(1)
var sampler_array: binding_array<sampler>;

@vertex
fn vertex_main(
	vertex: VertexInput,
	instance: InstanceInput,
) -> VertexOutput {

	var out: VertexOutput;

	// Skip expired particles
	if instance.expires < global_data.current_time.x {
		out.tween = 0.0;
		out.texture_index_a = u32(0);
		out.texture_index_b = u32(0);
		out.texture_coords_a = vec2(0.0, 0.0);
		out.texture_coords_b = vec2(0.0, 0.0);
		out.position = vec4<f32>(2.0, 2.0, 0.0, 1.0);
		return out;
	}

	let age = global_data.current_time.x - instance.created;


	// Apply transformations
	let angle = instance.angle + age * instance.angvel;

	var scale: f32 = instance.size / global_data.camera_zoom.x;
	var pos: vec2<f32> = vec2(
		vertex.position.x * scale * global_sprites[instance.sprite_index].aspect,
		vertex.position.y * scale
	);

	// Correct angle, since sprites point north and zero degrees is east
	pos = mat2x2(
		vec2(cos(angle - 1.5708), sin(angle - 1.5708)),
		vec2(-sin(angle - 1.5708), cos(angle - 1.5708))
	) * pos;

	var trans: vec2<f32> = (instance.position + (instance.velocity * age) - global_data.camera_position);

	pos = vec2(
		pos.x / global_data.window_aspect.x,
		pos.y
	);

	pos = pos + vec2(
		trans.x / (global_data.camera_zoom.x / 2.0) / global_data.window_aspect.x,
		trans.y / (global_data.camera_zoom.x / 2.0)
	);


	out.position = vec4(pos, 0.0, 1.0);

	if instance.expires - global_data.current_time.x <= instance.fade {
		out.fade = (instance.expires - global_data.current_time.x) / instance.fade;
	} else {
		out.fade = 1.0;
	}

	// Compute texture coordinates
	let frame = animate(instance.sprite_index, age, 0.0);
	out.tween = instance.texture_fade;

	let t = global_atlas[instance.texture_index.x];
	out.texture_index_a = u32(t.atlas_texture);
	out.texture_coords_a = vec2(t.xpos, t.ypos);
	if vertex.texture_coords.x == 1.0 {
		out.texture_coords_a = out.texture_coords_a + vec2(t.width, 0.0);
	}
	if vertex.texture_coords.y == 1.0 {
		out.texture_coords_a = out.texture_coords_a + vec2(0.0, t.height);
	}

	let b = global_atlas[instance.texture_index.y];
	out.texture_index_b = u32(b.atlas_texture);
	out.texture_coords_b = vec2(b.xpos, b.ypos);
	if vertex.texture_coords.x == 1.0 {
		out.texture_coords_b = out.texture_coords_b + vec2(b.width, 0.0);
	}
	if vertex.texture_coords.y == 1.0 {
		out.texture_coords_b = out.texture_coords_b + vec2(0.0, b.height);
	}

	return out;
}


@fragment
fn fragment_main(in: VertexOutput) -> @location(0) vec4<f32> {

	return mix(
		textureSampleLevel(
			texture_array[in.texture_index_a],
			sampler_array[0],
			in.texture_coords_a,
			0.0
		).rgba,
		textureSampleLevel(
			texture_array[in.texture_index_b],
			sampler_array[0],
			in.texture_coords_b,
			0.0
		).rgba,
		in.tween
	) * vec4(1.0, 1.0, 1.0, in.fade);
}