trash-slots/curtain.js

function Curtain(game, camera) {
	this.system = null;
	this.canvas = null;

	this.duration = 5000;
	this.timer = 0;
	this.opacity = 0;

	this.onComplete = null;

	this.state = "idle";


	this.init = function(systemObject, canvas) {
		this.system = systemObject;
		this.canvas = canvas;
	};

	this.close = function(duration,  onComplete) {
		this.duration = duration;
		this.onComplete = onComplete;
		this.opacity = 1;
		this.timer = 0;
		this.state = "closing";

	}

	this.open = function(duration, onComplete) {
		this.duration = duration;
		this.onComplete = onComplete;
		this.opacity = 0;
		this.timer = 0;
		this.state = "opening";
	}

	this.updateDelta = function(delta) {
		if(this.state == "idle") {
			return;
		}

		this.timer += delta * (1000 / 60);
		if(this.timer - (this.duration / 8) >= this.duration) {
			this.state = "idle";
			this.onComplete();
			return;
		}
		
		this.opacity = (this.timer / (this.duration - (this.duration / 8)));
	};

	this.draw = function(context) {
		if(this.state == "idle") {
			return;
		}
		
		if(this.state == "closing") {
			context.fillStyle = "#000000";
			context.globalAlpha = Math.min(1, Math.max(0, this.opacity));
			context.beginPath();
			context.rect(0, 0, this.canvas.width, this.canvas.height);
			context.fill();
		}
		
		if(this.state == "opening") {
			context.fillStyle = "#000000";
			context.globalAlpha = Math.min(1, Math.max(0, 1 - this.opacity));
			context.beginPath();
			context.rect(0, 0, this.canvas.width, this.canvas.height);
			context.fill();
		}

		context.globalAlpha = 1;
	};
};