Easy HTML5 2D physics with PhysicsJS

Let me show you a new and promising physics engine you can use in your HTML5 games: PhysicsJS by Well Caffeinated.

It’s a modular, extendable, and easy-to-use physics engine for javascript which is still under development and misses some features and most of the documentation, but there are a couple of things I liked a lot, such as:

* easiness to create your own renderer, there’s also a contest about this topic

* simple and quick way to detect a body given a point

* interesting world and timestep management

So here my version of the classic “create a box/remove a box”:

Click on an empty space on the canvas to create a box, or on an existing box to remove it.

Here is the commented source code:

<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title>PhysicsJS</title>
  		<script src="physicsjs-full.js"></script>
  		<script src="http://code.jquery.com/jquery-2.0.3.min.js"></script>
		<style>
			body {
				margin:0px;
			}
			#canvasid{
				background-color:black;
			}
		</style>
		<script>
			$(document).ready(function(){
				// world declaration
				var world = Physics();
				// creation of the renderer which will draw the world
				var renderer = Physics.renderer("canvas",{
    					el: "canvasid",	// canvas element id
					width: 640,		// canvas width
					height: 480,		// canvas height
					meta: false		// setting it to "true" will display FPS
				});	
				// adding the renderer to the world
				world.add(renderer);
				// what happens at every iteration step? We render (show the world)
				world.subscribe("step",function(){
    					world.render();
				});
				// this is the default gravity
				var gravity = Physics.behavior("constant-acceleration",{
    					acc: {
						x:0, 
						y:0.0004
					} 
				});
				// adding gravity to the world
				world.add(gravity);
				// adding collision detection with canvas edges
				world.add(Physics.behavior("edge-collision-detection", {
      				aabb: Physics.aabb(0, 0, 640, 480),
	      			restitution: 0
  				}));
  				// bodies will react to forces such as gravity
  				world.add(Physics.behavior("body-impulse-response"));
  				// enabling collision detection among bodies
  				world.add(Physics.behavior("body-collision-detection"));
				world.add(Physics.behavior("sweep-prune"));
			     $("#canvasid").click(function(e){
			     	// checking canvas coordinates for the mouse click
					var offset = $(this).offset();
					var px = e.pageX - offset.left;
     				var py = e.pageY - offset.top;
     				// this is the way physicsjs handles 2d vectors, similar at Box2D's b2Vec
					var mousePos = Physics.vector();
     				mousePos.set(px,py);
     				// finding a body under mouse position
     				var body = world.findOne({
						$at: mousePos
					})
					// there isn't any body under mouse position, going to create a new box
					if(!body){
				     	world.add(Physics.body("convex-polygon",{
        						x: px,
        						y: py,
        						vertices: [
        							{x:0, y:0},
        							{x:0, y:60},
        							{x:60, y:60},
        							{x:60, y:0}
        
    							],
    							restitution:0.5,
      					}));
					}
					else{
						// there is a body under mouse position, let's remove it
						world.removeBody(body);
					} 
				})
				// handling timestep
  				Physics.util.ticker.subscribe(function(time,dt){
    					world.step(time);
  				});
				Physics.util.ticker.start();
			})
		</script>		
	</head>
<body>
	<canvas id="canvasid" width="640" height="480"></canvas>
</body>

</html>

And you can also download the source code with all required libraries.

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