Refactored to use canvasUtility

index.html

@@ -9,7 +9,7 @@
     </body>
 
     <style>
-        #canvas > canvas {
+        #canvas {
             width: 500px;
             height: 500px;
             border: 1px solid black;

ts/app.ts

@@ -1,21 +1,27 @@
+import CanvasUtil from "./canvas-util/canvasUtil.js";
+import Coordinates from "./canvas-util/coordinates.js";
+
 class CanvasReceiverController {
-    private canvasDiv: HTMLDivElement;
     private canvas!: HTMLCanvasElement;
-    private ctx!: CanvasRenderingContext2D | null;
+    private canvasDiv: HTMLDivElement;
+    private canvasUtil: CanvasUtil;
     private ws: WebSocket;
-    private coordinates?: Coordinates;
 
     /**
      * Represents whether the app is waiting for the first coordinates of a draw path. If lineTo
      * is called with the first pair of coordinates, every path will be connected. Therefore this
      * variable is needed to prevent drawing a line to the first pair of coordinates.
      */
-    private firstCoordinates: boolean = false;
+     private firstCoordinates: boolean = false;
 
     constructor() {
         this.canvasDiv = document.querySelector('#canvas') as HTMLDivElement;
+        this.canvasUtil = new CanvasUtil(this.canvasDiv.offsetWidth, this.canvasDiv.offsetHeight);
 
         this.createCanvas();
+        if (!this.canvasUtil.isCanvasApiSupported) {
+            alert('Canvas API unavailable, drawing will not work!');
+        }
 
         this.ws = new WebSocket('ws://localhost:8081', 'json');
 
@@ -23,16 +29,9 @@ class CanvasReceiverController {
         this.ws.onopen = () => this.ws.send('RECEIVER');
     }
 
-    private createCanvas() {
+    createCanvas() {
-        this.canvas = document.createElement('canvas');
+        const canvas = this.canvasUtil.getCanvas();
-        this.canvasDiv.appendChild(this.canvas);
+        this.canvasDiv.appendChild(canvas);
-        this.canvas.width = this.canvas.offsetWidth;
-        this.canvas.height = this.canvas.offsetHeight;
-        if (!this.canvas.getContext) {
-            alert('Canvas API unavailable, drawing will not work!');
-        } else {
-            this.ctx = this.canvas.getContext('2d');
-        }
     }
 
     processMessage(message: MessageEvent<any>) {
@@ -54,56 +53,30 @@ class CanvasReceiverController {
 
     startDrawing() {
         console.log('Received START command');
-        if (!this.ctx) {
-            return;
-        }
         this.firstCoordinates = true;
     }
 
     stopDrawing() {
-        if (!this.ctx) {
+        this.canvasUtil.stopPath();
-            return;
-        }
     }
 
-    private clear() {
+    clear() {
         this.canvasDiv.removeChild(this.canvas);
+        this.canvasUtil.recreateCanvas();
         this.createCanvas();
     }
 
     draw(coordinates: Coordinates) {
-        if (!this.ctx) {
-            return;
-        }
-
-        this.ctx.beginPath();
-
-        if (this.coordinates) {
-            this.ctx.moveTo(this.coordinates.x, this.coordinates.y);
-        }
-
         if (this.firstCoordinates) {
             this.firstCoordinates = false;
-        } else {
+            this.canvasUtil.startPath(coordinates);
-            this.ctx.lineTo(coordinates.x, coordinates.y);
         }
 
-        this.ctx.stroke();
+        this.canvasUtil.draw(coordinates);
-        this.coordinates = coordinates;
     }
 }
 
 
-class Coordinates {
-    public x: number;
-    public y: number;
-
-    constructor(x: number, y: number) {
-        this.x = x;
-        this.y = y;
-    }
-}
-
 const app = new CanvasReceiverController();
 
 export { app };

ts/canvas-util/canvasUtil.ts

@@ -0,0 +1,77 @@
+import Coordinates from "./coordinates.js";
+
+export default class CanvasUtil {
+    private canvas?: HTMLCanvasElement;
+    private ctx?: CanvasRenderingContext2D | null;
+
+    private canvasWidth: number;
+    private canvasHeight: number;
+
+    private currentCoordinates: Coordinates;
+
+    public paths: Coordinates[][] = [];
+    public currentPath: Coordinates[] = [];
+
+    constructor(canvasWidth: number, canvasHeight: number) {
+        this.currentCoordinates = new Coordinates(0, 0);
+        this.canvasWidth = canvasWidth;
+        this.canvasHeight = canvasHeight;
+        this.createCanvas();
+    }
+
+    public getCanvas(): HTMLCanvasElement {
+        if (!this.canvas) {
+            this.createCanvas();
+        }
+        return this.canvas!;
+    }
+
+    public recreateCanvas() {
+        this.createCanvas();
+        return this.canvas;
+    }
+
+    public startPath(coordinates: Coordinates) {
+        this.currentPath.push(coordinates);
+        this.currentCoordinates = coordinates;
+    }
+
+    public stopPath() {
+        if (this.currentPath.length) {
+            this.paths.push(this.currentPath);
+        }
+        this.currentPath = [];
+    }
+
+    public draw(coordinates: Coordinates) {
+        if (!this.ctx) {
+            throw new Error('No canvas context available!');
+        }
+
+        this.ctx.beginPath();
+        this.ctx.moveTo(this.currentCoordinates.x, this.currentCoordinates.y);
+        this.ctx.lineTo(coordinates.x, coordinates.y);
+        this.ctx.lineWidth = 1;
+        this.ctx.stroke();
+
+        this.currentPath.push(coordinates);
+        this.currentCoordinates = coordinates;
+    }
+
+    /**
+     * States whether the canvas API is supported by the browser and whether
+     * drawing will work
+     */
+    public get isCanvasApiSupported(): boolean {
+        return !!this.ctx;
+    }
+
+    private createCanvas() {
+        this.canvas = document.createElement('canvas');
+        this.canvas.width = this.canvasWidth;
+        this.canvas.height = this.canvasHeight;
+        if (this.canvas.getContext) {
+            this.ctx = this.canvas.getContext('2d');
+        }
+    }
+}

ts/canvas-util/coordinates.ts

@@ -0,0 +1,9 @@
+export default class Coordinates {
+    public x: number;
+    public y: number;
+
+    constructor(x: number, y: number) {
+        this.x = x;
+        this.y = y;
+    }
+}