// INCLUDE: global uniform header

struct InstanceInput {
	@location(2) texture_index: vec2<u32>,
	@location(3) texture_fade: f32,
	@location(4) object_index: u32,
	@location(5) color: vec4<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) texture_index_a: u32,
	@location(2) texture_coords_a: vec2<f32>,
	@location(3) texture_index_b: u32,
	@location(4) texture_coords_b: vec2<f32>,
	@location(5) color: vec4<f32>,
};


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

fn transform_vertex(obj: ObjectData, vertex_position: vec2<f32>, texture_index: u32) -> vec4<f32> {
	// Object scale
	var scale: f32 = obj.size / (global_data.camera_zoom * obj.zpos);
	if obj.is_child == 1u {
		scale /= objects[obj.parent].zpos;
	}

	let texture = global_atlas[texture_index];

	// Apply scale and sprite aspect
	// Note that our mesh starts centered at (0, 0). This is important!
	var pos: vec2<f32> = vec2(
		vertex_position.x * scale * (texture.width / texture.height),
		vertex_position.y * scale
	);
	
	// Apply rotation
	pos = mat2x2(
		vec2(cos(obj.angle - 1.5708), sin(obj.angle - 1.5708)),
		vec2(-sin(obj.angle - 1.5708), cos(obj.angle - 1.5708))
	) * pos;


	// Correct for screen aspect, preserving height
	// This must be done AFTER rotation.
	// (It's thus done later if this is a child)
	if obj.is_child == u32(0) {
		pos = vec2(
			pos.x / global_data.window_aspect,
			pos.y
		);
	}

	// Translate
	//
	// Note that we divide camera zoom by two.
	// The height of the viewport is `zoom` in game units,
	// but it's 2 in screen units (since coordinates range from -1 to 1)
	if obj.is_child == u32(0) {
		let trans = (
			vec2(obj.xpos, obj.ypos) -
			vec2(global_data.camera_position_x, global_data.camera_position_y)
		) / obj.zpos;
		pos = pos + vec2(
			trans.x / (global_data.camera_zoom / 2.0) / global_data.window_aspect,
			trans.y / (global_data.camera_zoom / 2.0)
		);
	}

	if obj.is_child == u32(1) {

		let parent = objects[obj.parent];

		// Apply translation relative to parent
		// Note that obj.zpos is ignored
		pos = pos + vec2(
			obj.xpos / (global_data.camera_zoom / 2.0) / global_data.window_aspect,
			obj.ypos / (global_data.camera_zoom / 2.0)
		) / parent.zpos;

		// Apply parent's rotation
		pos = mat2x2(
			vec2(cos(parent.angle - 1.5708), sin(parent.angle - 1.5708)),
			vec2(-sin(parent.angle - 1.5708), cos(parent.angle - 1.5708))
		) * pos;

		// Correct for screen aspect, preserving height
		pos = vec2(
			pos.x / global_data.window_aspect,
			pos.y
		);

		// Apply parent's translation
		let ptrans = (
			vec2(parent.xpos, parent.ypos) - 
			vec2(global_data.camera_position_x, global_data.camera_position_y)
		) / parent.zpos;
		pos = pos + vec2(
			ptrans.x / (global_data.camera_zoom / 2.0) / global_data.window_aspect,
			ptrans.y / (global_data.camera_zoom / 2.0)
		);
	}

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

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

	// Pick texture size by the size of the visible texture
	// (texture index 0 is special, it's the "hidden" texture)
	if instance.texture_index.x == 0u && instance.texture_index.y == 0u {
		out.position = vec4<f32>(0.0, 0.0, 0.0, 1.0);
	} else if instance.texture_index.x == 0u {
		out.position = transform_vertex(
			objects[instance.object_index],
			vertex.position.xy,
			instance.texture_index.y
		);
	} else if instance.texture_index.y == 0u {
		out.position = transform_vertex(
			objects[instance.object_index],
			vertex.position.xy,
			instance.texture_index.x
		);
	} else {
		out.position = transform_vertex(
			objects[instance.object_index],
			vertex.position.xy,
			instance.texture_index.x
		);
	}

	out.color = instance.color;
	out.tween = instance.texture_fade;

	// Texture 0 is special, it's the empty texture
	if instance.texture_index.x == 0u {
		out.texture_index_a = 0u;
		out.texture_coords_a = vec2(0.0, 0.0);
	} else {
		let t = global_atlas[instance.texture_index.x];
		out.texture_index_a = 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);
		}
	}

	if instance.texture_index.y == 0u {
		out.texture_index_b = u32(0u);
		out.texture_coords_b = vec2(0.0, 0.0);
	} else {
		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> {

	var texture_a: vec4<f32> = vec4(0.0, 0.0, 0.0, 0.0);
	if !(
		(in.texture_index_a == 0u) &&
		(in.texture_coords_a.x == 0.0) &&
		(in.texture_coords_a.y == 0.0)
	) {
		texture_a = textureSampleLevel(
			texture_array[in.texture_index_a],
			sampler_array[0],
			in.texture_coords_a,
			0.0
		).rgba;
	}


	var texture_b: vec4<f32> = vec4(0.0, 0.0, 0.0, 0.0);
	if !(
		(in.texture_index_b == 0u) &&
		(in.texture_coords_b.x == 0.0) &&
		(in.texture_coords_b.y == 0.0)
	) {
		texture_b = textureSampleLevel(
			texture_array[in.texture_index_b],
			sampler_array[0],
			in.texture_coords_b,
			0.0
		).rgba;
	}

	let color = mix(
		texture_a,
		texture_b,
		in.tween
	) * in.color;


	return color;
}