phaser/src/textures/CanvasTexture.js

/**
 * @author       Richard Davey <rich@photonstorm.com>
 * @copyright    2018 Photon Storm Ltd.
 * @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
 */

var Class = require('../utils/Class');
var IsSizePowerOfTwo = require('../math/pow2/IsSizePowerOfTwo');
var Texture = require('./Texture');

/**
 * @classdesc
 * A Canvas Texture is a special kind of Texture that is backed by an HTML Canvas Element as its source.
 *
 * You can use the properties of this texture to draw to the canvas element directly, using all of the standard
 * canvas operations available in the browser. Any Game Object can be given this texture and will render with it.
 *
 * Note: When running under WebGL the Canvas Texture needs to re-generate its base WebGLTexture and reupload it to
 * the GPU every time you modify it, otherwise the changes you make to this texture will not be visible. To do this
 * you should call `CanvasTexture.refresh()` once you are finished with your changes to the canvas. Try and keep
 * this to a minimum, especially on large canvas sizes, or you may inadvertently thrash the GPU by constantly uploading
 * texture data to it. This restriction does not apply if using the Canvas Renderer.
 * 
 * It starts with only one frame that covers the whole of the canvas. You can add further frames, that specify
 * sections of the canvas using the `add` method.
 * 
 * Should you need to resize the canvas use the `setSize` method so that it accurately updates all of the underlying
 * texture data as well. Forgetting to do this (i.e. by changing the canvas size directly from your code) could cause
 * graphical errors.
 *
 * @class CanvasTexture
 * @extends Phaser.Textures.Texture
 * @memberOf Phaser.Textures
 * @constructor
 * @since 3.7.0
 *
 * @param {Phaser.Textures.TextureManager} manager - A reference to the Texture Manager this Texture belongs to.
 * @param {string} key - The unique string-based key of this Texture.
 * @param {HTMLCanvasElement} source - The canvas element that is used as the base of this texture.
 * @param {integer} width - The width of the canvas.
 * @param {integer} height - The height of the canvas.
 */
var CanvasTexture = new Class({

    Extends: Texture,

    initialize:

    function CanvasTexture (manager, key, source, width, height)
    {
        Texture.call(this, manager, key, source, width, height);

        this.add('__BASE', 0, 0, 0, width, height);

        /**
         * A reference to the Texture Source of this Canvas.
         *
         * @name Phaser.Textures.TextureManager#_source
         * @type {Phaser.Textures.TextureSource}
         * @private
         * @since 3.7.0
         */
        this._source = this.frames['__BASE'].source;

        /**
         * The source Canvas Element.
         *
         * @name Phaser.Textures.TextureManager#canvas
         * @readOnly
         * @type {HTMLCanvasElement}
         * @since 3.7.0
         */
        this.canvas = this._source.image;

        /**
         * The 2D Canvas Rendering Context.
         *
         * @name Phaser.Textures.TextureManager#canvas
         * @readOnly
         * @type {CanvasRenderingContext2D}
         * @since 3.7.0
         */
        this.context = this.canvas.getContext('2d');

        /**
         * The width of the Canvas.
         * This property is read-only, if you wish to change use `setSize`.
         *
         * @name Phaser.Textures.TextureManager#width
         * @readOnly
         * @type {integer}
         * @since 3.7.0
         */
        this.width = width;

        /**
         * The height of the Canvas.
         * This property is read-only, if you wish to change use `setSize`.
         *
         * @name Phaser.Textures.TextureManager#height
         * @readOnly
         * @type {integer}
         * @since 3.7.0
         */
        this.height = height;
    },

    /**
     * This should be called manually if you are running under WebGL.
     * It will refresh the WebGLTexture from the Canvas source. Only call this if you know that the
     * canvas has changed, as there is a significant GPU texture allocation cost involved in doing so.
     *
     * @method Phaser.Textures.CanvasTexture#refresh
     * @since 3.7.0
     *
     * @return {Phaser.Textures.CanvasTexture} This CanvasTexture.
     */
    refresh: function ()
    {
        this._source.update();

        return this;
    },

    /**
     * Gets the Canvas Element.
     *
     * @method Phaser.Textures.CanvasTexture#getCanvas
     * @since 3.7.0
     *
     * @return {HTMLCanvasElement} The Canvas DOM element this texture is using.
     */
    getCanvas: function ()
    {
        return this.canvas;
    },

    /**
     * Gets the 2D Canvas Rendering Context.
     *
     * @method Phaser.Textures.CanvasTexture#getContext
     * @since 3.7.0
     *
     * @return {CanvasRenderingContext2D} The Canvas Rendering Context this texture is using.
     */
    getContext: function ()
    {
        return this.context;
    },

    /**
     * Clears this Canvas Texture, resetting it back to transparent.
     *
     * @method Phaser.Textures.CanvasTexture#clear
     * @since 3.7.0
     *
     * @return {Phaser.Textures.CanvasTexture} The Canvas Texture.
     */
    clear: function ()
    {
        this.context.clearRect(0, 0, this.width, this.height);

        return this;
    },

    /**
     * Changes the size of this Canvas Texture.
     *
     * @method Phaser.Textures.CanvasTexture#setSize
     * @since 3.7.0
     *
     * @param {integer} width - The new width of the Canvas.
     * @param {integer} [height] - The new height of the Canvas. If not given it will use the width as the height.
     *
     * @return {Phaser.Textures.CanvasTexture} The Canvas Texture.
     */
    setSize: function (width, height)
    {
        if (height === undefined) { height = width; }

        if (width !== this.width || height !== this.height)
        {
            //  Update the Canvas
            this.canvas.width = width;
            this.canvas.height = height;

            //  Update the Texture Source
            this._source.width = width;
            this._source.height = height;
            this._source.isPowerOf2 = IsSizePowerOfTwo(width, height);

            //  Update the Frame
            this.frames['__BASE'].setSize(width, height, 0, 0);

            this.refresh();
        }

        return this;
    }

});

module.exports = CanvasTexture;