# Source: Viewport.js

    import {Vector2} from "./math/Vector2.js";
    import {Matrix} from "./math/Matrix.js";
    import {UUID} from "./math/UUID.js";

    /**
     * Viewport defines the user view into the content being rendered, similar to a camera it defines the size of the content, rotation and position of the content.
     *
     * The viewport can be moved, rotated and scaled to navigate the virtual canvas.
     *
     * @class
     * @param {Element} canvas Canvas DOM element where the viewport is being rendered.
     */
    function Viewport(canvas)
    {
    	/**
    	 * UUID of the object.
    	 *
    	 * @type {string}
    	 */
    	this.uuid = UUID.generate();

    	/**
    	 * Canvas DOM element where the viewport is being rendered.
    	 *
    	 * @type {Element}
    	 */
    	this.canvas = canvas;

    	/**
    	 * Position of the viewport.
    	 *
    	 * @type {Vector2}
    	 */
    	this.position = new Vector2(0, 0);

    	/**
    	 * Center point of the viewport. Relative to the size of the canvas.
    	 *
    	 * Rotation and zoom is applied relative to this point.
    	 *
    	 * @type {Vector2}
    	 */
    	this.center = new Vector2(0, 0);

    	/**
    	 * Scale of the object.
    	 *
    	 * @type {number}
    	 */
    	this.scale = 1.0

    	/**
    	 * Rotation of the object relative to its center.
    	 *
    	 * @type {number}
    	 */
    	this.rotation = 0.0;

    	/**
    	 * Local transformation matrix applied to the object.
    	 *
    	 * @type {Matrix}
    	 */
    	this.matrix = new Matrix();

    	/**
    	 * Inverse of the local transformation matrix.
    	 *
    	 * Used to transform points from local to global coordinates.
    	 *
    	 * @type {Matrix}
    	 */
    	this.inverseMatrix = new Matrix();

    	/**
    	 * If true the matrix is updated before rendering the object.
    	 *
    	 * Disable this if you want to update the matrix manually.
    	 *
    	 * @type {boolean}
    	 */
    	this.matrixNeedsUpdate = true;

    	/**
    	 * Flag to indicate if the viewport should move when scaling.
    	 *
    	 * For some application its easier to focus the target if the viewport moves to the pointer location while scaling.
    	 */
    	this.centerOnPointer = false;

    	/**
    	 * Value of the initial point of rotation if the viewport is being rotated.
    	 *
    	 * Is set to null when the viewport is not being rotated.
    	 */
    	this.rotationPoint = null;
    }

    /**
     * Calculate and update the viewport transformation matrix.
     *
     * Also updates the inverse matrix of the viewport.
     */
    Viewport.prototype.updateMatrix = function()
    {
    	if(this.matrixNeedsUpdate)
    	{
    		this.matrix.m = [1, 0, 0, 1, this.position.x , this.position.y];

    		if(this.center.x !== 0.0 || this.center.y !== 0.0) {
    			this.matrix.multiply(new Matrix([1, 0, 0, 1, this.center.x, this.center.y]));
    		}

    		if(this.rotation !== 0.0)
    		{
    			var c = Math.cos(this.rotation);
    			var s = Math.sin(this.rotation);
    			this.matrix.multiply(new Matrix([c, s, -s, c, 0, 0]));
    		}

    		if(this.scale !== 1.0)
    		{
    			this.matrix.multiply(new Matrix([this.scale, 0, 0, this.scale, 0, 0]));
    		}

    		if(this.center.x !== 0.0 || this.center.y !== 0.0) {
    			this.matrix.multiply(new Matrix([1, 0, 0, 1, -this.center.x, -this.center.y]));
    		}

    		this.inverseMatrix = this.matrix.getInverse();
    		this.matrixNeedsUpdate = false;
    	}
    };

    /**
     * Center the viewport relative to a object.
     *
     * The position of the object is used a central point, this method does not consider "box" attributes or other strucures in the object.
     *
     * Uses the object's local transformation matrix and the canvas size to calculate the new position of the viewport.
     *
     * @param {Object2D} object Object to be centered on the viewport.
     * @param {Element} canvas Canvas element where the image is drawn.
     */
    Viewport.prototype.centerObject = function(object, canvas)
    {
    	var position = object.globalMatrix.transformPoint(new Vector2());
    	position.multiplyScalar(-this.scale);
    	position.x += canvas.width / 2;
    	position.y += canvas.height / 2;

    	this.position.copy(position);
    	this.matrixNeedsUpdate = true;
    };

    export {Viewport};