Fire JS Bin - Ball-Pool

var canvas;

var delta = [ 0, 0 ];
var stage = [ window.screenX, window.screenY, window.innerWidth, window.innerHeight ];
getBrowserDimensions();

var themes = [ [ "#10222B", "#95AB63", "#BDD684", "#E2F0D6", "#F6FFE0" ],
    [ "#362C2A", "#732420", "#BF734C", "#FAD9A0", "#736859" ],
    [ "#0D1114", "#102C2E", "#695F4C", "#EBBC5E", "#FFFBB8" ],
    [ "#2E2F38", "#FFD63E", "#FFB54B", "#E88638", "#8A221C" ],
    [ "#121212", "#E6F2DA", "#C9F24B", "#4D7B85", "#23383D" ],
    [ "#343F40", "#736751", "#F2D7B6", "#BFAC95", "#8C3F3F" ],
    [ "#000000", "#2D2B2A", "#561812", "#B81111", "#FFFFFF" ],
    [ "#333B3A", "#B4BD51", "#543B38", "#61594D", "#B8925A" ] ];
var theme;

var worldAABB, world, iterations = 1, timeStep = 1 / 20;

var walls = [];
var wall_thickness = 200;
var wallsSetted = false;

var bodies, elements, text;

var createMode = false;
var destroyMode = false;

var isMouseDown = false;
var mouseJoint;
var mouseX = 0;
var mouseY = 0;

var PI2 = Math.PI * 2;

var timeOfLastTouch = 0;

init();
play();

function init() {

canvas = document.getElementById( 'canvas' );

document.onmousedown = onDocumentMouseDown;
  document.onmouseup = onDocumentMouseUp;
  document.onmousemove = onDocumentMouseMove;
  document.ondblclick = onDocumentDoubleClick;

document.addEventListener( 'touchstart', onDocumentTouchStart, false );
  document.addEventListener( 'touchmove', onDocumentTouchMove, false );
  document.addEventListener( 'touchend', onDocumentTouchEnd, false );

// init box2d

worldAABB = new b2AABB();
  worldAABB.minVertex.Set( -200, -200 );
  worldAABB.maxVertex.Set( screen.width + 200, screen.height + 200 );

world = new b2World( worldAABB, new b2Vec2( 0, 0 ), true );

setWalls();
  reset();
}

function play() {

setInterval( loop, 1000 / 40 );
}

function reset() {

var i;

if ( bodies ) {

for ( i = 0; i < bodies.length; i++ ) {

var body = bodies[ i ]
      canvas.removeChild( body.GetUserData().element );
      world.DestroyBody( body );
      body = null;
    }
  }

// color theme
  theme = themes[ Math.random() * themes.length >> 0 ];
  document.body.style[ 'backgroundColor' ] = theme[ 0 ];

bodies = [];
  elements = [];

createInstructions();

for( i = 0; i < 10; i++ ) {

createBall();

}

//

function onDocumentMouseDown() {

isMouseDown = true;
  return false;
}

function onDocumentMouseUp() {

isMouseDown = false;
  return false;
}

function onDocumentMouseMove( event ) {

mouseX = event.clientX;
  mouseY = event.clientY;
}

function onDocumentDoubleClick() {

reset();
}

function onDocumentTouchStart( event ) {

if( event.touches.length == 1 ) {

event.preventDefault();

// Faking double click for touch devices

var now = new Date().getTime();

if ( now - timeOfLastTouch < 250 ) {

reset();
      return;
    }

timeOfLastTouch = now;

mouseX = event.touches[ 0 ].pageX;
    mouseY = event.touches[ 0 ].pageY;
    isMouseDown = true;
  }
}

function onDocumentTouchMove( event ) {

if ( event.touches.length == 1 ) {

event.preventDefault();

mouseX = event.touches[ 0 ].pageX;
    mouseY = event.touches[ 0 ].pageY;

}

function onDocumentTouchEnd( event ) {

if ( event.touches.length == 0 ) {

event.preventDefault();
    isMouseDown = false;

}

//

function createInstructions() {

var size = 250;

var element = document.createElement( 'div' );
  element.width = size;
  element.height = size;  
  element.style.position = 'absolute';
  element.style.left = -200 + 'px';
  element.style.top = -200 + 'px';
  element.style.cursor = "default";

canvas.appendChild(element);
  elements.push( element );

var circle = document.createElement( 'canvas' );
  circle.width = size;
  circle.height = size;

var graphics = circle.getContext( '2d' );

graphics.fillStyle = theme[ 3 ];
  graphics.beginPath();
  graphics.arc( size * .5, size * .5, size * .5, 0, PI2, true );
  graphics.closePath();
  graphics.fill();

element.appendChild( circle );

text = document.createElement( 'div' );
 text.onSelectStart = null;
 text.innerHTML = 'Hello! This is how it works: 1. Drag a ball. 2. Click on the background. 3. Shake your browser. 4. Double click. 5. Play!';
 text.style.color = theme[1];
 text.style.position = 'absolute';
 text.style.left = '0px';
 text.style.top = '0px';
 text.style.fontFamily = 'Georgia';
 text.style.textAlign = 'center';
 element.appendChild(text);

text.style.left = ((250 - text.clientWidth) / 2) +'px';
  text.style.top = ((250 - text.clientHeight) / 2) +'px';

var b2body = new b2BodyDef();

var circle = new b2CircleDef();
  circle.radius = size / 2;
  circle.density = 1;
  circle.friction = 0.3;
  circle.restitution = 0.3;
  b2body.AddShape(circle);
  b2body.userData = {element: element};

b2body.position.Set( Math.random() * stage[2], Math.random() * -200 );
  b2body.linearVelocity.Set( Math.random() * 400 - 200, Math.random() * 400 - 200 );
  bodies.push( world.CreateBody(b2body) );  
}

function createBall( x, y ) {

var x = x || Math.random() * stage[2];
  var y = y || Math.random() * -200;

var size = (Math.random() * 100 >> 0) + 20;

var element = document.createElement("canvas");
  element.width = size;
  element.height = size;
  element.style['position'] = 'absolute';
  element.style['left'] = -200 + 'px';
  element.style['top'] = -200 + 'px';

var graphics = element.getContext("2d");

var num_circles = Math.random() * 10 >> 0;

for (var i = size; i > 0; i-= (size/num_circles)) {

graphics.fillStyle = theme[ (Math.random() * 4 >> 0) + 1];
    graphics.beginPath();
    graphics.arc(size * .5, size * .5, i * .5, 0, PI2, true); 
    graphics.closePath();
    graphics.fill();
  }

canvas.appendChild(element);

elements.push( element );

var b2body = new b2BodyDef();

var circle = new b2CircleDef();
  circle.radius = size >> 1;
  circle.density = 1;
  circle.friction = 0.3;
  circle.restitution = 0.3;
  b2body.AddShape(circle);
  b2body.userData = {element: element};

b2body.position.Set( x, y );
  b2body.linearVelocity.Set( Math.random() * 400 - 200, Math.random() * 400 - 200 );
  bodies.push( world.CreateBody(b2body) );
}

//

function loop() {

if (getBrowserDimensions()) {

setWalls();

}

delta[0] += (0 - delta[0]) * .5;
  delta[1] += (0 - delta[1]) * .5;

world.m_gravity.x = 0 + delta[0];
  world.m_gravity.y = 350 + delta[1];

mouseDrag();
  world.Step(timeStep, iterations);

for (i = 0; i < bodies.length; i++) {

var body = bodies[i];
    var element = elements[i];

element.style.left = (body.m_position0.x - (element.width >> 1)) + 'px';
    element.style.top = (body.m_position0.y - (element.height >> 1)) + 'px';

if (element.tagName == 'DIV') {

var rotationStyle = 'rotate(' + (body.m_rotation0 * 57.2957795) + 'deg)';
      text.style.WebkitTransform = rotationStyle;
      text.style.MozTransform = rotationStyle;
      text.style.OTransform = rotationStyle;

}

// .. BOX2D UTILS

function createBox(world, x, y, width, height, fixed) {

if (typeof(fixed) == 'undefined') {

fixed = true;

}

var boxSd = new b2BoxDef();

if (!fixed) {

boxSd.density = 1.0;

}

boxSd.extents.Set(width, height);

var boxBd = new b2BodyDef();
  boxBd.AddShape(boxSd);
  boxBd.position.Set(x,y);

return world.CreateBody(boxBd);

}

function mouseDrag()
{
  // mouse press
  if (createMode) {

createBall( mouseX, mouseY );

} else if (isMouseDown && !mouseJoint) {

var body = getBodyAtMouse();

if (body) {

var md = new b2MouseJointDef();
      md.body1 = world.m_groundBody;
      md.body2 = body;
      md.target.Set(mouseX, mouseY);
      md.maxForce = 30000 * body.m_mass;
      md.timeStep = timeStep;
      mouseJoint = world.CreateJoint(md);
      body.WakeUp();

} else {

createMode = true;

}

// mouse release
  if (!isMouseDown) {

createMode = false;
    destroyMode = false;

if (mouseJoint) {

world.DestroyJoint(mouseJoint);
      mouseJoint = null;

}

// mouse move
  if (mouseJoint) {

var p2 = new b2Vec2(mouseX, mouseY);
    mouseJoint.SetTarget(p2);
  }
}

function getBodyAtMouse() {

// Make a small box.
  var mousePVec = new b2Vec2();
  mousePVec.Set(mouseX, mouseY);

var aabb = new b2AABB();
  aabb.minVertex.Set(mouseX - 1, mouseY - 1);
  aabb.maxVertex.Set(mouseX + 1, mouseY + 1);

// Query the world for overlapping shapes.
  var k_maxCount = 10;
  var shapes = new Array();
  var count = world.Query(aabb, shapes, k_maxCount);
  var body = null;

for (var i = 0; i < count; ++i) {

if (shapes[i].m_body.IsStatic() == false) {

if ( shapes[i].TestPoint(mousePVec) ) {

body = shapes[i].m_body;
        break;

}

return body;

}

function setWalls() {

if (wallsSetted) {

world.DestroyBody(walls[0]);
    world.DestroyBody(walls[1]);
    world.DestroyBody(walls[2]);
    world.DestroyBody(walls[3]);

walls[0] = null; 
    walls[1] = null;
    walls[2] = null;
    walls[3] = null;
  }

walls[0] = createBox(world, stage[2] / 2, - wall_thickness, stage[2], wall_thickness);
  walls[1] = createBox(world, stage[2] / 2, stage[3] + wall_thickness, stage[2], wall_thickness);
  walls[2] = createBox(world, - wall_thickness, stage[3] / 2, wall_thickness, stage[3]);
  walls[3] = createBox(world, stage[2] + wall_thickness, stage[3] / 2, wall_thickness, stage[3]);

wallsSetted = true;

}

// BROWSER DIMENSIONS

function getBrowserDimensions() {

var changed = false;

if (stage[0] != window.screenX) {

delta[0] = (window.screenX - stage[0]) * 50;
    stage[0] = window.screenX;
    changed = true;

}

if (stage[1] != window.screenY) {

delta[1] = (window.screenY - stage[1]) * 50;
    stage[1] = window.screenY;
    changed = true;

}

if (stage[2] != window.innerWidth) {

stage[2] = window.innerWidth;
    changed = true;

}

if (stage[3] != window.innerHeight) {

stage[3] = window.innerHeight;
    changed = true;

}

return changed;

}