S2JS - Rotating, flipping, pointing - another game : Rotating key handling

Next we'll add a listener so we can rotate whenever a key is pressed, using the left and right arrows.

Adding the listener:

addEventListener("keydown", MyKeyDownHandler);

And the function that gets called when the keydown event is heard:

Our code changes the angle of rotation by 15 degrees for each key press.

If this sort of code seems unfamiliar, then it may be worth going back and reviewing Responding to Keys.

<html> <body> <canvas id="myCanvas" width=300 height=300 style="background-color:MediumSeaGreen"> </canvas> <script> var ctx = myCanvas.getContext("2d"); // Get the drawing context for the canvas var FPS = 40; // How many frames per second function MySprite (img_url) { this.x = 0; this.y = 0; this.visible= true; this.velocity_x = 0; this.velocity_y = 0; this.MyImg = new Image(); this.MyImg.src = img_url ; this.angle= 0; // How many degrees we are rotated } MySprite.prototype.Do_Frame_Things = function() { if (this.visible) ctx.drawImage(this.MyImg, this.x, this.y); // draw the thing this.x = this.x + this.velocity_x; this.y = this.y + this.velocity_y; // move the thing } function MyKeyDownHandler (MyEvent) { if (MyEvent.keyCode == 37) {thing.angle = thing.angle - 15}; // left if (MyEvent.keyCode == 39) {thing.angle = thing.angle + 15}; // right MyEvent.preventDefault(); } addEventListener("keydown", MyKeyDownHandler); var thing= new MySprite("http://s2js.com/img/etc/cat_grumpy.png"); thing.x=120; thing.y=120; function Do_a_Frame () { ctx.clearRect(0, 0, myCanvas.width, myCanvas.height); // clear the frame thing.Do_Frame_Things(); // let the thing do its thing } setInterval(Do_a_Frame, 1000/FPS); // set my frame renderer </script> </body> </html>