src/manager/DOMManager.js

import Manager from './Manager';

/**
 * Manages the connection between the DOM and the Game & Engine.
 * 
 * The DOMManager sets up and holds reference to the DOM elements required to display the game.
 */
export class _DOMManager extends Manager {
    /**
     * Initializes defaults for the DOMManager to hold once started.
     */
    constructor() {
        super();
        this.canvas = null;
        this.GL = null;

        this.canvasWidth = 0;
        this.canvasHeight = 0;
        this.canvasDPIWidth = 0;
        this.canvasDPIHeight = 0;
    }

    /**
     * Loads the canvas & setup for WebGL.
     */
    start() {
        this.loadCanvas();
        this.adjust();
    }
    
    /**
     * Loads the canvas & sets up a WebGL2 context to be used by the engine by the id 'game'. If nothing is happening on screen,
     * ensure that the canvas you are using has this id in its HTML tag.
     */
    loadCanvas() {
        this.canvas = document.getElementById('game');
        if (this.canvas == null)
            console.error("Error finding DOM Canvas. The canvas requires an id='game'");
        this.GL = this.canvas.getContext('webgl2', {alpha: false, antialias: false, powerPreference: 'high-performance', preserveDrawingBuffer: true,});
        if (this.GL == null) {
            console.error("WebGL2 Context could not be built. This browser does not support WebGL2.");
        }
        window.addEventListener('resize', () => {
            this.adjust();
        })
    }

    /*
    Any function that plays with sizing, ratio, or other 
    DOM elements with the canvas should call this after.
    */
    adjust() {
        if (this.GL == null)
            return;
        this.GL.imageSmoothingEnabled = false;
        this.GL.webkitImageSmoothingEnabled = false;

        this.canvasWidth = this.canvas.width;
        this.canvasHeight = this.canvas.height;
        this.canvasDPIWidth = this.canvasWidth / this.canvas.clientWidth;
        this.canvasDPIHeight = this.canvasHeight / this.canvas.clientHeight;
    }
}

/**
 * Singleton reference to the DOM Manager.
 */
const DOMManager = new _DOMManager();
export default DOMManager;