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 = '<center><span style="color:' + theme[0] + ';font-size:28px;">creative technology</span></center>';
          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;
                          // text.style.MsTransform = 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;
  
  }