S2JS - Rotating, flipping, pointing - another game : Rotating solution #1

There's a pretty straightforward solution, which is that we change the rotation, do our drawing, then "unrotate". It's not the best solution, but it will definitely work:

ctx.rotate(this.angle * Math.PI / 180); if (this.visible) ctx.drawImage(this.MyImg, this.x, this.y); ctx.rotate( -this.angle * Math.PI / 180);

We rotate, we draw, then we unrotate (note the use of the minus sign before "this.angle" in the second call to rotate).

Try the left or right keys now.

Slightly better?

<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 } 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); MySprite.prototype.Do_Frame_Things = function() { ctx.rotate(this.angle * Math.PI / 180); // rotate if (this.visible) ctx.drawImage(this.MyImg, this.x, this.y); // draw the thing ctx.rotate(-this.angle * Math.PI / 180); // unrotate so its not cumulative this.x = this.x + this.velocity_x; this.y = this.y + this.velocity_y; // move the thing } 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>