S2JS - Objects: a game with more sprites : Putting it together

Let's flesh things out a bit.

I've moved most of the code we've just talked about into the preface area, just to clear the decks.

I've also added a keydown handler, with the same sort of left/right handling we've seen before.

The only difference is that instead of dealing with separate "bug_x" and "bug_y" variables, we're just accessing the ".x" and ".y" properties of the "bug" variable.

<html> <head> <title> Bat avoiding game using Objects</title> </head> <body> <canvas id="myCanvas" width=300 height=300 style="background:url('/img/etc/night city.png'); background-size: cover"> </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 ; } 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 ImagesTouching(thing1, thing2) { // // This function detects whether two MySprites are touching - very useful function // if (!thing1.visible || !thing2.visible) return false; if (thing1.x >= thing2.x + thing2.MyImg.width || thing1.x + thing1.MyImg.width <= thing2.x) return false; if (thing1.y >= thing2.y + thing2.MyImg.height || thing1.y + thing1.MyImg.height <= thing2.y) return false; return true; } var bug = new MySprite("http://s2js.com/img/etc/ladybug.png"); // The bug function Do_a_Frame () { ctx.clearRect(0, 0, myCanvas.width, myCanvas.height); // clear the background bug.y = myCanvas.height - bug.MyImg.height; // ensure bug always at bottom of canvas bug.Do_Frame_Things(); // bug does what bugs do } function MyKeyDownHandler (MyEvent) { if (MyEvent.keyCode == 37 && bug.x > 0) {bug.x = bug.x - 10}; // left if (MyEvent.keyCode == 39 && bug.x + bug.MyImg.width < myCanvas.width) {bug.x = bug.x+10}; // right } addEventListener("keydown", MyKeyDownHandler); // listen for keystrokes setInterval(Do_a_Frame, 1000/FPS); </script> </body> </html>