Update network error template to new design

chrome/renderer/resources/offline.js

+// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+(function() {
+'use strict';
+/**
+ * T-Rex runner.
+ * @param {string} outerContainerId Outer containing element id.
+ * @param {object} opt_config
+ * @constructor
+ * @export
+ */
+function Runner(outerContainerId, opt_config) {
+  // Singleton
+  if (Runner.instance_) {
+    return Runner.instance_;
+  }
+  Runner.instance_ = this;
+
+  this.outerContainerEl = document.querySelector(outerContainerId);
+  this.containerEl = null;
+
+  this.config = opt_config || Runner.config;
+
+  this.dimensions = Runner.defaultDimensions;
+
+  this.canvas = null;
+  this.canvasCtx = null;
+
+  this.tRex = null;
+
+  this.distanceMeter = null;
+  this.distanceRan = 0;
+
+  this.highestScore = 0;
+
+  this.time = 0;
+  this.runningTime = 0;
+  this.msPerFrame = 1000 / FPS;
+  this.currentSpeed = this.config.SPEED;
+
+  this.obstacles = [];
+
+  this.started = false;
+  this.activated = false;
+  this.crashed = false;
+  this.paused = false;
+
+  this.resizeTimerId_ = null;
+
+  this.playCount = 0;
+
+  // Sound FX.
+  this.audioBuffer = null;
+  this.soundFx = {};
+
+  // Global web audio context for playing sounds.
+  this.audioContext = new AudioContext();
+
+  // Images.
+  this.images = {};
+  this.imagesLoaded = 0;
+  this.loadImages();
+}
+window['Runner'] = Runner;
+
+
+/**
+ * Default game width.
+ * @const
+ */
+var DEFAULT_WIDTH = 600;
+
+/**
+ * Frames per second.
+ * @const
+ */
+var FPS = 60;
+
+/** @const */
+var IS_HIDPI = window.devicePixelRatio > 1;
+
+/** @const */
+var IS_MOBILE = window.navigator.userAgent.indexOf('Mobi') > -1;
+
+/** @const */
+var IS_TOUCH_ENABLED = 'ontouchstart' in window;
+
+
+/**
+ * Default game configuration.
+ * @enum {number}
+ */
+Runner.config = {
+  ACCELERATION: 0.001,
+  BG_CLOUD_SPEED: 0.2,
+  BOTTOM_PAD: 10,
+  CLEAR_TIME: 3000,
+  CLOUD_FREQUENCY: 0.5,
+  GAMEOVER_CLEAR_TIME: 750,
+  GAP_COEFFICIENT: 0.6,
+  GRAVITY: 0.6,
+  INITIAL_JUMP_VELOCITY: 12,
+  MAX_CLOUDS: 6,
+  MAX_OBSTACLE_LENGTH: 3,
+  MAX_SPEED: 12,
+  MIN_JUMP_HEIGHT: 35,
+  MOBILE_SPEED_COEFFICIENT: 1.2,
+  RESOURCE_TEMPLATE_ID: 'audio-resources',
+  SPEED: 6,
+  SPEED_DROP_COEFFICIENT: 3
+};
+
+
+/**
+ * Default dimensions.
+ * @enum {string}
+ */
+Runner.defaultDimensions = {
+  WIDTH: DEFAULT_WIDTH,
+  HEIGHT: 150
+};
+
+
+/**
+ * CSS class names.
+ * @enum {string}
+ */
+Runner.classes = {
+  CANVAS: 'runner-canvas',
+  CONTAINER: 'runner-container',
+  CRASHED: 'crashed',
+  ICON: 'icon-offline',
+  TOUCH_CONTROLLER: 'controller'
+};
+
+
+/**
+ * Image source urls.
+ * @enum {array.<object>}
+ */
+Runner.imageSources = {
+  LDPI: [
+    {name: 'CACTUS_LARGE', id: '1x-obstacle-large'},
+    {name: 'CACTUS_SMALL', id: '1x-obstacle-small'},
+    {name: 'CLOUD', id: '1x-cloud'},
+    {name: 'HORIZON', id: '1x-horizon'},
+    {name: 'RESTART', id: '1x-restart'},
+    {name: 'TEXT_SPRITE', id: '1x-text'},
+    {name: 'TREX', id: '1x-trex'}
+  ],
+  HDPI: [
+    {name: 'CACTUS_LARGE', id: '2x-obstacle-large'},
+    {name: 'CACTUS_SMALL', id: '2x-obstacle-small'},
+    {name: 'CLOUD', id: '2x-cloud'},
+    {name: 'HORIZON', id: '2x-horizon'},
+    {name: 'RESTART', id: '2x-restart'},
+    {name: 'TEXT_SPRITE', id: '2x-text'},
+    {name: 'TREX', id: '2x-trex'}
+  ]
+};
+
+
+/**
+ * Sound FX. Reference to the ID of the audio tag on interstitial page.
+ * @enum {string}
+ */
+Runner.sounds = {
+  BUTTON_PRESS: 'offline-sound-press',
+  HIT: 'offline-sound-hit',
+  SCORE: 'offline-sound-reached'
+};
+
+
+/**
+ * Key code mapping.
+ * @enum {object}
+ */
+Runner.keycodes = {
+  JUMP: {'38': 1, '32': 1},  // Up, spacebar
+  DUCK: {'40': 1},  // Down
+  RESTART: {'13': 1}  // Enter
+};
+
+
+/**
+ * Runner event names.
+ * @enum {string}
+ */
+Runner.events = {
+  ANIM_END: 'webkitAnimationEnd',
+  CLICK: 'click',
+  KEYDOWN: 'keydown',
+  KEYUP: 'keyup',
+  MOUSEDOWN: 'mousedown',
+  MOUSEUP: 'mouseup',
+  RESIZE: 'resize',
+  TOUCHEND: 'touchend',
+  TOUCHSTART: 'touchstart',
+  VISIBILITY: 'visibilitychange',
+  BLUR: 'blur',
+  FOCUS: 'focus',
+  LOAD: 'load'
+};
+
+
+Runner.prototype = {
+  /**
+   * Setting individual settings for debugging.
+   * @param {string} setting
+   * @param {*} value
+   */
+  updateConfigSetting: function(setting, value) {
+    if (setting in this.config && value != undefined) {
+      this.config[setting] = value;
+
+      switch (setting) {
+        case 'GRAVITY':
+        case 'MIN_JUMP_HEIGHT':
+        case 'SPEED_DROP_COEFFICIENT':
+          this.tRex.config[setting] = value;
+          break;
+        case 'INITIAL_JUMP_VELOCITY':
+          this.tRex.setJumpVelocity(value);
+          break;
+        case 'SPEED':
+          this.setSpeed(value);
+          break;
+      }
+    }
+  },
+
+  /**
+   * Load and cache the image assets from the page.
+   */
+  loadImages: function() {
+    var imageSources = IS_HIDPI ? Runner.imageSources.HDPI :
+        Runner.imageSources.LDPI;
+
+    var numImages = imageSources.length;
+
+    for (var i = numImages - 1; i >= 0; i--) {
+      var imgSource = imageSources[i];
+      this.images[imgSource.name] = document.getElementById(imgSource.id);
+    }
+    this.init();
+  },
+
+  /**
+   * Load and decode base 64 encoded sounds.
+   */
+  loadSounds: function() {
+    var resourceTemplate =
+        document.getElementById(this.config.RESOURCE_TEMPLATE_ID).content;
+
+    for (var sound in Runner.sounds) {
+      var soundSrc = resourceTemplate.getElementById(Runner.sounds[sound]).src;
+      soundSrc = soundSrc.substr(soundSrc.indexOf(',') + 1);
+      var buffer = decodeBase64ToArrayBuffer(soundSrc);
+
+      // Async, so no guarantee of order in array.
+      this.audioContext.decodeAudioData(buffer, function(index, audioData) {
+          this.soundFx[index] = audioData;
+        }.bind(this, sound));
+    }
+  },
+
+  /**
+   * Sets the game speed. Adjust the speed accordingly if on a smaller screen.
+   * @param {number} opt_speed
+   */
+  setSpeed: function(opt_speed) {
+    var speed = opt_speed || this.currentSpeed;
+
+    // Reduce the speed on smaller mobile screens.
+    if (this.dimensions.WIDTH < DEFAULT_WIDTH) {
+      var mobileSpeed = speed * this.dimensions.WIDTH / DEFAULT_WIDTH *
+          this.config.MOBILE_SPEED_COEFFICIENT;
+      this.currentSpeed = mobileSpeed > speed ? speed : mobileSpeed;
+    } else if (opt_speed) {
+      this.currentSpeed = opt_speed;
+    }
+  },
+
+  /**
+   * Game initialiser.
+   */
+  init: function() {
+    // Hide the static icon.
+    document.querySelector('.' + Runner.classes.ICON).style.visibility =
+        'hidden';
+
+    this.adjustDimensions();
+    this.setSpeed();
+
+    this.containerEl = document.createElement('div');
+    this.containerEl.className = Runner.classes.CONTAINER;
+
+    // Player canvas container.
+    this.canvas = createCanvas(this.containerEl, this.dimensions.WIDTH,
+        this.dimensions.HEIGHT, Runner.classes.PLAYER);
+
+    this.canvasCtx = this.canvas.getContext('2d');
+    this.canvasCtx.fillStyle = '#f7f7f7';
+    this.canvasCtx.fill();
+    Runner.updateCanvasScaling(this.canvas);
+
+    // Horizon contains clouds, obstacles and the ground.
+    this.horizon = new Horizon(this.canvas, this.images, this.dimensions,
+        this.config.GAP_COEFFICIENT);
+
+    // Distance meter
+    this.distanceMeter = new DistanceMeter(this.canvas,
+          this.images.TEXT_SPRITE, this.dimensions.WIDTH);
+
+    // Draw t-rex
+    this.tRex = new Trex(this.canvas, this.images.TREX);
+
+    this.outerContainerEl.appendChild(this.containerEl);
+
+    if (IS_MOBILE) {
+      this.createTouchController();
+    }
+
+    this.startListening();
+    this.update();
+    this.loadSounds();
+
+    window.addEventListener(Runner.events.RESIZE,
+        this.debounceResize.bind(this), false);
+  },
+
+  /**
+   * Create the touch controller. A div that covers whole screen.
+   */
+  createTouchController: function() {
+    this.touchController = document.createElement('div');
+    this.touchController.className = Runner.classes.TOUCH_CONTROLLER;
+  },
+
+  /**
+   * Debounce the resize event.
+   */
+  debounceResize: function() {
+    if (!this.resizeTimerId_) {
+      this.resizeTimerId_ =
+          setInterval(this.adjustDimensions.bind(this), 250);
+    }
+  },
+
+  /**
+   * Adjust game space dimensions on resize.
+   */
+  adjustDimensions: function() {
+    clearInterval(this.resizeTimerId_);
+    this.resizeTimerId_ = null;
+
+    var boxStyles = window.getComputedStyle(this.outerContainerEl);
+    var padding = Number(boxStyles.paddingLeft.substr(0,
+        boxStyles.paddingLeft.length - 2));
+
+    this.dimensions.WIDTH = this.outerContainerEl.offsetWidth - padding * 2;
+
+    // Redraw the elements back onto the canvas.
+    if (this.canvas) {
+      this.canvas.width = this.dimensions.WIDTH;
+      this.canvas.height = this.dimensions.HEIGHT;
+
+      Runner.updateCanvasScaling(this.canvas);
+
+      this.distanceMeter.calcXPos(this.dimensions.WIDTH);
+      this.clearCanvas();
+      this.horizon.update(0, 0, true);
+      this.tRex.update(0);
+
+      // Outer container and distance meter.
+      if (this.activated || this.crashed) {
+        this.containerEl.style.width = this.dimensions.WIDTH + 'px';
+        this.containerEl.style.height = this.dimensions.HEIGHT + 'px';
+        this.distanceMeter.update(0, Math.ceil(this.distanceRan));
+        this.stop();
+      } else {
+        this.tRex.draw(0, 0);
+      }
+
+      // Game over panel.
+      if (this.crashed && this.gameOverPanel) {
+        this.gameOverPanel.updateDimensions(this.dimensions.WIDTH);
+        this.gameOverPanel.draw();
+      }
+    }
+  },
+
+  /**
+   * Play the game intro.
+   * Canvas container width expands out to the full width.
+   */
+  playIntro: function() {
+    if (!this.started && !this.crashed) {
+      this.playingIntro = true;
+      this.tRex.playingIntro = true;
+
+      // CSS animation definition.
+      var keyframes = '@-webkit-keyframes intro { ' +
+            'from { width:' + Trex.config.WIDTH + 'px }' +
+            'to { width: ' + this.dimensions.WIDTH + 'px }' +
+          '}';
+      document.styleSheets[0].insertRule(keyframes, 0);
+
+      this.containerEl.addEventListener(Runner.events.ANIM_END,
+          this.startGame.bind(this));
+
+      this.containerEl.style.webkitAnimation = 'intro .4s ease-out 1 both';
+      this.containerEl.style.width = this.dimensions.WIDTH + 'px';
+
+      if (this.touchController) {
+        this.outerContainerEl.appendChild(this.touchController);
+      }
+      this.activated = true;
+      this.started = true;
+    } else if (this.crashed) {
+      this.restart();
+    }
+  },
+
+
+  /**
+   * Update the game status to started.
+   */
+  startGame: function() {
+    this.runningTime = 0;
+    this.playingIntro = false;
+    this.tRex.playingIntro = false;
+    this.containerEl.style.webkitAnimation = '';
+    this.playCount++;
+
+    // Handle tabbing off the page. Pause the current game.
+    window.addEventListener(Runner.events.VISIBILITY,
+          this.onVisibilityChange.bind(this), false);
+
+    window.addEventListener(Runner.events.BLUR,
+          this.onVisibilityChange.bind(this), false);
+
+    window.addEventListener(Runner.events.FOCUS,
+          this.onVisibilityChange.bind(this), false);
+  },
+
+  clearCanvas: function() {
+    this.canvasCtx.clearRect(0, 0, this.dimensions.WIDTH,
+        this.dimensions.HEIGHT);
+  },
+
+  /**
+   * Update the game frame.
+   */
+  update: function() {
+    this.drawPending = false;
+
+    var now = performance.now();
+    var deltaTime = now - (this.time || now);
+    this.time = now;
+
+    if (this.activated) {
+      this.clearCanvas();
+
+      if (this.tRex.jumping) {
+        this.tRex.updateJump(deltaTime, this.config);
+      }
+
+      this.runningTime += deltaTime;
+      var hasObstacles = this.runningTime > this.config.CLEAR_TIME;
+
+      // First jump triggers the intro.
+      if (this.tRex.jumpCount == 1 && !this.playingIntro) {
+        this.playIntro();
+      }
+
+      // The horizon doesn't move until the intro is over.
+      if (this.playingIntro) {
+        this.horizon.update(0, this.currentSpeed, hasObstacles);
+      } else {
+        deltaTime = !this.started ? 0 : deltaTime;
+        this.horizon.update(deltaTime, this.currentSpeed, hasObstacles);
+      }
+
+      // Check for collisions.
+      var collision = hasObstacles &&
+          checkForCollision(this.horizon.obstacles[0], this.tRex);
+
+      if (!collision) {
+        this.distanceRan += this.currentSpeed * deltaTime / this.msPerFrame;
+
+        if (this.currentSpeed < this.config.MAX_SPEED) {
+          this.currentSpeed += this.config.ACCELERATION;
+        }
+      } else {
+        this.gameOver();
+      }
+
+      if (this.distanceMeter.getActualDistance(this.distanceRan) >
+          this.distanceMeter.maxScore) {
+        this.distanceRan = 0;
+      }
+
+      var playAcheivementSound = this.distanceMeter.update(deltaTime,
+          Math.ceil(this.distanceRan));
+
+      if (playAcheivementSound) {
+        this.playSound(this.soundFx.SCORE);
+      }
+    }
+
+    if (!this.crashed) {
+      this.tRex.update(deltaTime);
+      this.raq();
+    }
+  },
+
+  /**
+   * Event handler.
+   */
+  handleEvent: function(e) {
+    return (function(evtType, events) {
+      switch (evtType) {
+        case events.KEYDOWN:
+        case events.TOUCHSTART:
+        case events.MOUSEDOWN:
+          this.onKeyDown(e);
+          break;
+        case events.KEYUP:
+        case events.TOUCHEND:
+        case events.MOUSEUP:
+          this.onKeyUp(e);
+          break;
+      }
+    }.bind(this))(e.type, Runner.events);
+  },
+
+  /**
+   * Bind relevant key / mouse / touch listeners.
+   */
+  startListening: function() {
+    // Keys.
+    document.addEventListener(Runner.events.KEYDOWN, this);
+    document.addEventListener(Runner.events.KEYUP, this);
+
+    if (IS_MOBILE) {
+      // Mobile only touch devices.
+      this.touchController.addEventListener(Runner.events.TOUCHSTART, this);
+      this.touchController.addEventListener(Runner.events.TOUCHEND, this);
+      this.containerEl.addEventListener(Runner.events.TOUCHSTART, this);
+    } else {
+      // Mouse.
+      document.addEventListener(Runner.events.MOUSEDOWN, this);
+      document.addEventListener(Runner.events.MOUSEUP, this);
+    }
+  },
+
+  /**
+   * Remove all listeners.
+   */
+  stopListening: function() {
+    document.removeEventListener(Runner.events.KEYDOWN, this);
+    document.removeEventListener(Runner.events.KEYUP, this);
+
+    if (IS_MOBILE) {
+      this.touchController.removeEventListener(Runner.events.TOUCHSTART, this);
+      this.touchController.removeEventListener(Runner.events.TOUCHEND, this);
+      this.containerEl.removeEventListener(Runner.events.TOUCHSTART, this);
+    } else {
+      document.removeEventListener(Runner.events.MOUSEDOWN, this);
+      document.removeEventListener(Runner.events.MOUSEUP, this);
+    }
+  },
+
+  /**
+   * Process keydown.
+   * @param {Event} e
+   */
+  onKeyDown: function(e) {
+    if (!this.crashed && (Runner.keycodes.JUMP[String(e.keyCode)] ||
+         e.type == Runner.events.TOUCHSTART)) {
+      if (!this.activated) {
+        this.activated = true;
+      }
+
+      if (!this.tRex.jumping) {
+        this.playSound(this.soundFx.BUTTON_PRESS);
+        this.tRex.startJump();
+      }
+    }
+
+    if (this.crashed && e.type == Runner.events.TOUCHSTART &&
+        e.currentTarget == this.containerEl) {
+      this.restart();
+    }
+
+    // Speed drop, activated only when jump key is not pressed.
+    if (Runner.keycodes.DUCK[e.keyCode] && this.tRex.jumping) {
+      e.preventDefault();
+      this.tRex.setSpeedDrop();
+    }
+  },
+
+
+  /**
+   * Process key up.
+   * @param {Event} e
+   */
+  onKeyUp: function(e) {
+    var keyCode = String(e.keyCode);
+    var isjumpKey = Runner.keycodes.JUMP[keyCode] ||
+       e.type == Runner.events.TOUCHEND ||
+       e.type == Runner.events.MOUSEDOWN;
+
+    if (this.isRunning() && isjumpKey) {
+      this.tRex.endJump();
+    } else if (Runner.keycodes.DUCK[keyCode]) {
+      this.tRex.speedDrop = false;
+    } else if (this.crashed) {
+      // Check that enough time has elapsed before allowing jump key to restart.
+      var deltaTime = performance.now() - this.time;
+
+      if (Runner.keycodes.RESTART[keyCode] ||
+         (e.type == Runner.events.MOUSEUP && e.target == this.canvas) ||
+         (deltaTime >= this.config.GAMEOVER_CLEAR_TIME &&
+         Runner.keycodes.JUMP[keyCode])) {
+        this.restart();
+      }
+    } else if (this.paused && isjumpKey) {
+      this.play();
+    }
+  },
+
+  /**
+   * RequestAnimationFrame wrapper.
+   */
+  raq: function() {
+    if (!this.drawPending) {
+      this.drawPending = true;
+      this.raqId = requestAnimationFrame(this.update.bind(this));
+    }
+  },
+
+  /**
+   * Whether the game is running.
+   * @return {boolean}
+   */
+  isRunning: function() {
+    return !!this.raqId;
+  },
+
+  /**
+   * Game over state.
+   */
+  gameOver: function() {
+    this.playSound(this.soundFx.HIT);
+    vibrate(200);
+
+    this.stop();
+    this.crashed = true;
+    this.distanceMeter.acheivement = false;
+
+    this.tRex.update(100, Trex.status.CRASHED);
+
+    // Game over panel.
+    if (!this.gameOverPanel) {
+      this.gameOverPanel = new GameOverPanel(this.canvas,
+          this.images.TEXT_SPRITE, this.images.RESTART,
+          this.dimensions);
+    } else {
+      this.gameOverPanel.draw();
+    }
+
+    // Update the high score.
+    if (this.distanceRan > this.highestScore) {
+      this.highestScore = Math.ceil(this.distanceRan);
+      this.distanceMeter.setHighScore(this.highestScore);
+    }
+
+    // Reset the time clock.
+    this.time = performance.now();
+  },
+
+  stop: function() {
+    this.activated = false;
+    this.paused = true;
+    cancelAnimationFrame(this.raqId);
+    this.raqId = 0;
+  },
+
+  play: function() {
+    if (!this.crashed) {
+      this.activated = true;
+      this.paused = false;
+      this.tRex.update(0, Trex.status.RUNNING);
+      this.time = performance.now();
+      this.update();
+    }
+  },
+
+  restart: function() {
+    if (!this.raqId) {
+      this.playCount++;
+      this.runningTime = 0;
+      this.activated = true;
+      this.crashed = false;
+      this.distanceRan = 0;
+      this.setSpeed(this.config.SPEED);
+
+      this.time = performance.now();
+      this.containerEl.classList.remove(Runner.classes.CRASHED);
+      this.clearCanvas();
+      this.distanceMeter.reset(this.highestScore);
+      this.horizon.reset();
+      this.tRex.reset();
+      this.playSound(this.soundFx.BUTTON_PRESS);
+
+      this.update();
+    }
+  },
+
+  /**
+   * Pause the game if the tab is not in focus.
+   */
+  onVisibilityChange: function(e) {
+    if (document.hidden || document.webkitHidden || e.type == 'blur') {
+      this.stop();
+    } else {
+      this.play();
+    }
+  },
+
+  /**
+   * Play a sound.
+   * @param {SoundBuffer} soundBuffer
+   */
+  playSound: function(soundBuffer) {
+    if (soundBuffer) {
+      var sourceNode = this.audioContext.createBufferSource();
+      sourceNode.buffer = soundBuffer;
+      sourceNode.connect(this.audioContext.destination);
+      sourceNode.start(0);
+    }
+  }
+};
+
+
+/**
+ * Updates the canvas size taking into
+ * account the backing store pixel ratio and
+ * the device pixel ratio.
+ *
+ * See article by Paul Lewis:
+ * http://www.html5rocks.com/en/tutorials/canvas/hidpi/
+ *
+ * @param {HTMLCanvasElement} canvas
+ * @param {number} opt_width
+ * @param {number} opt_height
+ * @return {boolean} Whether the canvas was scaled.
+ */
+Runner.updateCanvasScaling = function(canvas, opt_width, opt_height) {
+  var context = canvas.getContext('2d');
+
+  // Query the various pixel ratios
+  var devicePixelRatio = Math.floor(window.devicePixelRatio) || 1;
+  var backingStoreRatio = Math.floor(context.webkitBackingStorePixelRatio) || 1;
+  var ratio = devicePixelRatio / backingStoreRatio;
+
+  // Upscale the canvas if the two ratios don't match
+  if (devicePixelRatio !== backingStoreRatio) {
+
+    var oldWidth = opt_width || canvas.width;
+    var oldHeight = opt_height || canvas.height;
+
+    canvas.width = oldWidth * ratio;
+    canvas.height = oldHeight * ratio;
+
+    canvas.style.width = oldWidth + 'px';
+    canvas.style.height = oldHeight + 'px';
+
+    // Scale the context to counter the fact that we've manually scaled
+    // our canvas element.
+    context.scale(ratio, ratio);
+    return true;
+  }
+  return false;
+};
+
+
+/**
+ * Get random number.
+ * @param {number} min
+ * @param {number} max
+ * @param {number}
+ */
+function getRandomNum(min, max) {
+  return Math.floor(Math.random() * (max - min + 1)) + min;
+}
+
+
+/**
+ * Vibrate on mobile devices.
+ * @param {number} duration Duration of the vibration in milliseconds.
+ */
+function vibrate(duration) {
+  if (IS_MOBILE) {
+    window.navigator['vibrate'](duration);
+  }
+}
+
+
+/**
+ * Create canvas element.
+ * @param {HTMLElement} container Element to append canvas to.
+ * @param {number} width
+ * @param {number} height
+ * @param {string} opt_classname
+ * @return {HTMLCanvasElement}
+ */
+function createCanvas(container, width, height, opt_classname) {
+  var canvas = document.createElement('canvas');
+  canvas.className = opt_classname ? Runner.classes.CANVAS + ' ' +
+      opt_classname : Runner.classes.CANVAS;
+  canvas.width = width;
+  canvas.height = height;
+  container.appendChild(canvas);
+
+  return canvas;
+}
+
+
+/**
+ * Decodes the base 64 audio to ArrayBuffer used by Web Audio.
+ * @param {string} base64String
+ */
+function decodeBase64ToArrayBuffer(base64String) {
+  var len = (base64String.length / 4) * 3;
+  var str = atob(base64String);
+  var arrayBuffer = new ArrayBuffer(len);
+  var bytes = new Uint8Array(arrayBuffer);
+
+  for (var i = 0; i < len; i++) {
+    bytes[i] = str.charCodeAt(i);
+  }
+  return bytes.buffer;
+}
+
+
+//******************************************************************************
+
+
+/**
+ * Game over panel.
+ * @param {!HTMLCanvasElement} canvas
+ * @param {!HTMLImage} textSprite
+ * @param {!HTMLImage} restartImg
+ * @param {!Object} dimensions Canvas dimensions.
+ * @constructor
+ */
+function GameOverPanel(canvas, textSprite, restartImg, dimensions) {
+  this.canvas = canvas;
+  this.canvasCtx = canvas.getContext('2d');
+  this.canvasDimensions = dimensions;
+  this.textSprite = textSprite;
+  this.restartImg = restartImg;
+  this.draw();
+};
+
+
+/**
+ * Dimensions used in the panel.
+ * @enum {number}
+ */
+GameOverPanel.dimensions = {
+  TEXT_X: 0,
+  TEXT_Y: 13,
+  TEXT_WIDTH: 191,
+  TEXT_HEIGHT: 11,
+  RESTART_WIDTH: 36,
+  RESTART_HEIGHT: 32
+};
+
+
+GameOverPanel.prototype = {
+  /**
+   * Update the panel dimensions.
+   * @param {number} width New canvas width.
+   * @param {number} opt_height Optional new canvas height.
+   */
+  updateDimensions: function(width, opt_height) {
+    this.canvasDimensions.WIDTH = width;
+    if (opt_height) {
+      this.canvasDimensions.HEIGHT = opt_height;
+    }
+  },
+
+  /**
+   * Draw the panel.
+   */
+  draw: function() {
+    var dimensions = GameOverPanel.dimensions;
+
+    var centerX = this.canvasDimensions.WIDTH / 2;
+
+    // Game over text.
+    var textSourceX = dimensions.TEXT_X;
+    var textSourceY = dimensions.TEXT_Y;
+    var textSourceWidth = dimensions.TEXT_WIDTH;
+    var textSourceHeight = dimensions.TEXT_HEIGHT;
+
+    var textTargetX = Math.round(centerX - (dimensions.TEXT_WIDTH / 2));
+    var textTargetY = Math.round((this.canvasDimensions.HEIGHT - 25) / 3);
+    var textTargetWidth = dimensions.TEXT_WIDTH;
+    var textTargetHeight = dimensions.TEXT_HEIGHT;
+
+    var restartSourceWidth = dimensions.RESTART_WIDTH;
+    var restartSourceHeight = dimensions.RESTART_HEIGHT;
+    var restartTargetX = centerX - (dimensions.RESTART_WIDTH / 2);
+    var restartTargetY = this.canvasDimensions.HEIGHT / 2;
+
+    if (IS_HIDPI) {
+      textSourceY *= 2;
+      textSourceX *= 2;
+      textSourceWidth *= 2;
+      textSourceHeight *= 2;
+      restartSourceWidth *= 2;
+      restartSourceHeight *= 2;
+    }
+
+    // Game over text from sprite.
+    this.canvasCtx.drawImage(this.textSprite,
+        textSourceX, textSourceY, textSourceWidth, textSourceHeight,
+        textTargetX, textTargetY, textTargetWidth, textTargetHeight);
+
+    // Restart button.
+    this.canvasCtx.drawImage(this.restartImg, 0, 0,
+        restartSourceWidth, restartSourceHeight,
+        restartTargetX, restartTargetY, dimensions.RESTART_WIDTH,
+        dimensions.RESTART_HEIGHT);
+  }
+};
+
+
+//******************************************************************************
+
+/**
+ * Check for a collision.
+ * @param {!Obstacle} obstacle
+ * @param {!Trex} tRex T-rex object.
+ * @param {HTMLCanvasContext} opt_canvasCtx Optional canvas context for drawing
+ *    collision boxes.
+ * @return {Array.<CollisionBox>}
+ */
+function checkForCollision(obstacle, tRex, opt_canvasCtx) {
+  var obstacleBoxXPos = Runner.defaultDimensions.WIDTH + obstacle.xPos;
+
+  // Adjustments are made to the bounding box as there is a 1 pixel white
+  // border around the t-rex and obstacles.
+  var tRexBox = new CollisionBox(
+      tRex.xPos + 1,
+      tRex.yPos + 1,
+      tRex.config.WIDTH - 2,
+      tRex.config.HEIGHT - 2);
+
+  var obstacleBox = new CollisionBox(
+      obstacle.xPos + 1,
+      obstacle.yPos + 1,
+      obstacle.typeConfig.width * obstacle.size - 2,
+      obstacle.typeConfig.height - 2);
+
+  // Debug outer box
+  if (opt_canvasCtx) {
+    drawCollisionBoxes(opt_canvasCtx, tRexBox, obstacleBox);
+  }
+
+  // Simple outer bounds check.
+  if (boxCompare(tRexBox, obstacleBox)) {
+    var collisionBoxes = obstacle.collisionBoxes;
+    var tRexCollisionBoxes = Trex.collisionBoxes;
+
+    // Detailed axis aligned box check.
+    for (var t = 0; t < tRexCollisionBoxes.length; t++) {
+      for (var i = 0; i < collisionBoxes.length; i++) {
+        // Adjust the box to actual positions.
+        var adjTrexBox =
+            createAdjustedCollisionBox(tRexCollisionBoxes[t], tRexBox);
+        var adjObstacleBox =
+            createAdjustedCollisionBox(collisionBoxes[i], obstacleBox);
+        var crashed = boxCompare(adjTrexBox, adjObstacleBox);
+
+        // Draw boxes for debug.
+        if (opt_canvasCtx) {
+          drawCollisionBoxes(opt_canvasCtx, adjTrexBox, adjObstacleBox);
+        }
+
+        if (crashed) {
+          return [adjTrexBox, adjObstacleBox];
+        }
+      }
+    }
+  }
+  return false;
+};
+
+
+/**
+ * Adjust the collision box.
+ * @param {!CollisionBox} box The original box.
+ * @param {!CollisionBox} adjustment Adjustment box.
+ * @return {CollisionBox} The adjusted collision box object.
+ */
+function createAdjustedCollisionBox(box, adjustment) {
+  return new CollisionBox(
+      box.x + adjustment.x,
+      box.y + adjustment.y,
+      box.width,
+      box.height);
+};
+
+
+/**
+ * Draw the collision boxes for debug.
+ */
+function drawCollisionBoxes(canvasCtx, tRexBox, obstacleBox) {
+  canvasCtx.save();
+  canvasCtx.strokeStyle = '#f00';
+  canvasCtx.strokeRect(tRexBox.x, tRexBox.y,
+  tRexBox.width, tRexBox.height);
+
+  canvasCtx.strokeStyle = '#0f0';
+  canvasCtx.strokeRect(obstacleBox.x, obstacleBox.y,
+  obstacleBox.width, obstacleBox.height);
+  canvasCtx.restore();
+};
+
+
+/**
+ * Compare two collision boxes for a collision.
+ * @param {CollisionBox} tRexBox
+ * @param {CollisionBox} obstacleBox
+ * @return {boolean} Whether the boxes intersected.
+ */
+function boxCompare(tRexBox, obstacleBox) {
+  var crashed = false;
+  var tRexBoxX = tRexBox.x;
+  var tRexBoxY = tRexBox.y;
+
+  var obstacleBoxX = obstacleBox.x;
+  var obstacleBoxY = obstacleBox.y;
+
+  // Axis-Aligned Bounding Box method.
+  if (tRexBox.x < obstacleBoxX + obstacleBox.width &&
+      tRexBox.x + tRexBox.width > obstacleBoxX &&
+      tRexBox.y < obstacleBox.y + obstacleBox.height &&
+      tRexBox.height + tRexBox.y > obstacleBox.y) {
+    crashed = true;
+  }
+
+  return crashed;
+};
+
+
+//******************************************************************************
+
+/**
+ * Collision box object.
+ * @param {number} x X position.
+ * @param {number} y Y Position.
+ * @param {number} w Width.
+ * @param {number} h Height.
+ */
+function CollisionBox(x, y, w, h) {
+  this.x = x;
+  this.y = y;
+  this.width = w;
+  this.height = h;
+};
+
+
+//******************************************************************************
+
+/**
+ * Obstacle.
+ * @param {HTMLCanvasCtx} canvasCtx
+ * @param {Obstacle.type} type
+ * @param {image} obstacleImg Image sprite.
+ * @param {Object} dimensions
+ * @param {number} gapCoefficient Mutipler in determining the gap.
+ * @param {number} speed
+ */
+function Obstacle(canvasCtx, type, obstacleImg, dimensions,
+    gapCoefficient, speed) {
+
+  this.canvasCtx = canvasCtx;
+  this.image = obstacleImg;
+  this.typeConfig = type;
+  this.gapCoefficient = gapCoefficient;
+  this.size = getRandomNum(1, Obstacle.MAX_OBSTACLE_LENGTH);
+  this.dimensions = dimensions;
+  this.remove = false;
+  this.xPos = 0;
+  this.yPos = this.typeConfig.yPos;
+  this.width = 0;
+  this.collisionBoxes = [];
+  this.gap = 0;
+
+  this.init(speed);
+};
+
+/**
+ * Coefficient for calculating the maximum gap.
+ * @const
+ */
+Obstacle.MAX_GAP_COEFFICIENT = 1.5;
+
+/**
+ * Maximum obstacle grouping count.
+ * @const
+ */
+Obstacle.MAX_OBSTACLE_LENGTH = 3,
+
+
+Obstacle.prototype = {
+  /**
+   * Initialise the DOM for the obstacle.
+   * @param {number} speed
+   */
+  init: function(speed) {
+    this.cloneCollisionBoxes();
+
+    // Only allow sizing if we're at the right speed.
+    if (this.size > 1 && this.typeConfig.multipleSpeed > speed) {
+      this.size = 1;
+    }
+
+    this.width = this.typeConfig.width * this.size;
+    this.xPos = this.dimensions.WIDTH - this.width;
+
+    this.draw();
+
+    // Make collision box adjustments,
+    // Central box is adjusted to the size as one box.
+    //      ____        ______        ________
+    //    _|   |-|    _|     |-|    _|       |-|
+    //   | |<->| |   | |<--->| |   | |<----->| |
+    //   | | 1 | |   | |  2  | |   | |   3   | |
+    //   |_|___|_|   |_|_____|_|   |_|_______|_|
+    //
+    if (this.size > 1) {
+      this.collisionBoxes[1].width = this.width - this.collisionBoxes[0].width -
+          this.collisionBoxes[2].width;
+      this.collisionBoxes[2].x = this.width - this.collisionBoxes[2].width;
+    }
+
+    this.gap = this.getGap(this.gapCoefficient, speed);
+  },
+
+  /**
+   * Draw and crop based on size.
+   */
+  draw: function() {
+    var sourceWidth = this.typeConfig.width;
+    var sourceHeight = this.typeConfig.height;
+
+    if (IS_HIDPI) {
+      sourceWidth = sourceWidth * 2;
+      sourceHeight = sourceHeight * 2;
+    }
+
+    // Sprite
+    var sourceX = (sourceWidth * this.size) * (0.5 * (this.size - 1));
+    this.canvasCtx.drawImage(this.image,
+      sourceX, 0,
+      sourceWidth * this.size, sourceHeight,
+      this.xPos, this.yPos,
+      this.typeConfig.width * this.size, this.typeConfig.height);
+  },
+
+  /**
+   * Obstacle frame update.
+   * @param {number} deltaTime
+   * @param {number} speed
+   */
+  update: function(deltaTime, speed) {
+    if (!this.remove) {
+      this.xPos -= Math.floor((speed * FPS / 1000) * deltaTime);
+      this.draw();
+
+      if (!this.isVisible()) {
+        this.remove = true;
+      }
+    }
+  },
+
+  /**
+   * Calculate a random gap size.
+   * - Minimum gap gets wider as speed increses
+   * @param {number} gapCoefficient
+   * @param {number} speed
+   * @return {number} The gap size.
+   */
+  getGap: function(gapCoefficient, speed) {
+    var minGap = Math.round(this.width * speed +
+          this.typeConfig.minGap * gapCoefficient);
+    var maxGap = Math.round(minGap * Obstacle.MAX_GAP_COEFFICIENT);
+    return getRandomNum(minGap, maxGap);
+  },
+
+  /**
+   * Check if obstacle is visible.
+   * @return {boolean} Whether the obstacle is in the game area.
+   */
+  isVisible: function() {
+    return this.xPos + this.width > 0;
+  },
+
+  /**
+   * Make a copy of the collision boxes, since these will change based on
+   * obstacle type and size.
+   */
+  cloneCollisionBoxes: function() {
+    var collisionBoxes = this.typeConfig.collisionBoxes;
+
+    for (var i = collisionBoxes.length - 1; i >= 0; i--) {
+      this.collisionBoxes[i] = new CollisionBox(collisionBoxes[i].x,
+          collisionBoxes[i].y, collisionBoxes[i].width,
+          collisionBoxes[i].height);
+    }
+  }
+};
+
+
+/**
+ * Obstacle definitions.
+ * minGap: minimum pixel space betweeen obstacles.
+ * multipleSpeed: Speed at which multiples are allowed.
+ */
+Obstacle.types = [
+  {
+    type: 'CACTUS_SMALL',
+    className: ' cactus cactus-small ',
+    width: 17,
+    height: 35,
+    yPos: 105,
+    multipleSpeed: 3,
+    minGap: 120,
+    collisionBoxes: [
+      new CollisionBox(0, 7, 5, 27),
+      new CollisionBox(4, 0, 6, 34),
+      new CollisionBox(10, 4, 7, 14)
+    ]
+  },
+  {
+    type: 'CACTUS_LARGE',
+    className: ' cactus cactus-large ',
+    width: 25,
+    height: 50,
+    yPos: 90,
+    multipleSpeed: 6,
+    minGap: 120,
+    collisionBoxes: [
+      new CollisionBox(0, 12, 7, 38),
+      new CollisionBox(8, 0, 7, 49),
+      new CollisionBox(13, 10, 10, 38)
+    ]
+  }
+];
+
+
+//******************************************************************************
+/**
+ * T-rex game character.
+ * @param {HTMLCanvas} canvas
+ * @param {HTMLImage} image Character image.
+ * @constructor
+ */
+function Trex(canvas, image) {
+  this.canvas = canvas;
+  this.canvasCtx = canvas.getContext('2d');
+  this.image = image;
+  this.xPos = 0;
+  this.yPos = 0;
+  // Position when on the ground.
+  this.groundYPos = 0;
+  this.currentFrame = 0;
+  this.currentAnimFrames = [];
+  this.blinkDelay = 0;
+  this.animStartTime = 0;
+  this.timer = 0;
+  this.msPerFrame = 1000 / FPS;
+  this.config = Trex.config;
+  // Current status.
+  this.status = Trex.status.WAITING;
+
+  this.jumping = false;
+  this.jumpVelocity = 0;
+  this.reachedMinHeight = false;
+  this.speedDrop = false;
+  this.jumpCount = 0;
+  this.jumpspotX = 0;
+
+  this.init();
+};
+
+
+/**
+ * T-rex player config.
+ * @enum {number}
+ */
+Trex.config = {
+  DROP_VELOCITY: -5,
+  GRAVITY: 0.6,
+  HEIGHT: 47,
+  INIITAL_JUMP_VELOCITY: -10,
+  INTRO_DURATION: 1500,
+  MAX_JUMP_HEIGHT: 30,
+  MIN_JUMP_HEIGHT: 30,
+  SPEED_DROP_COEFFICIENT: 3,
+  SPRITE_WIDTH: 262,
+  START_X_POS: 50,
+  WIDTH: 44
+};
+
+
+/**
+ * Used in collision detection.
+ * @type {Array.<CollisionBox>}
+ */
+Trex.collisionBoxes = [
+  new CollisionBox(1, -1, 30, 26),
+  new CollisionBox(32, 0, 8, 16),
+  new CollisionBox(10, 35, 14, 8),
+  new CollisionBox(1, 24, 29, 5),
+  new CollisionBox(5, 30, 21, 4),
+  new CollisionBox(9, 34, 15, 4)
+];
+
+
+/**
+ * Animation states.
+ * @enum {string}
+ */
+Trex.status = {
+  CRASHED: 'CRASHED',
+  JUMPING: 'JUMPING',
+  RUNNING: 'RUNNING',
+  WAITING: 'WAITING'
+};
+
+/**
+ * Blinking coefficient.
+ * @const
+ */
+Trex.BLINK_TIMING = 7000;
+
+
+/**
+ * Animation config for different states.
+ * @enum {object}
+ */
+Trex.animFrames = {
+  WAITING: {
+    frames: [44, 0],
+    msPerFrame: 1000 / 3
+  },
+  RUNNING: {
+    frames: [88, 132],
+    msPerFrame: 1000 / 12
+  },
+  CRASHED: {
+    frames: [220],
+    msPerFrame: 1000 / 60
+  },
+  JUMPING: {
+    frames: [0],
+    msPerFrame: 1000 / 60
+  }
+};
+
+
+Trex.prototype = {
+  /**
+   * T-rex player initaliser.
+   * Sets the t-rex to blink at random intervals.
+   */
+  init: function() {
+    this.blinkDelay = this.setBlinkDelay();
+    this.groundYPos = Runner.defaultDimensions.HEIGHT - this.config.HEIGHT -
+        Runner.config.BOTTOM_PAD;
+    this.yPos = this.groundYPos;
+    this.minJumpHeight = this.groundYPos - this.config.MIN_JUMP_HEIGHT;
+
+    this.draw(0, 0);
+    this.update(0, Trex.status.WAITING);
+  },
+
+  /**
+   * Setter for the jump velocity.
+   * The approriate drop velocity is also set.
+   */
+  setJumpVelocity: function(setting) {
+    this.config.INIITAL_JUMP_VELOCITY = -setting;
+    this.config.DROP_VELOCITY = -setting / 2;
+  },
+
+  /**
+   * Set the animation status.
+   * @param {!number} deltaTime
+   * @param {Trex.status} status Optional status to switch to.
+   */
+  update: function(deltaTime, opt_status) {
+    this.timer += deltaTime;
+
+    // Update the status.
+    if (opt_status) {
+      this.status = opt_status;
+      this.currentFrame = 0;
+      this.msPerFrame = Trex.animFrames[opt_status].msPerFrame;
+      this.currentAnimFrames = Trex.animFrames[opt_status].frames;
+
+      if (opt_status == Trex.status.WAITING) {
+        this.animStartTime = performance.now();
+        this.setBlinkDelay();
+      }
+    }
+
+    // Game intro animation, T-rex moves in from the left.
+    if (this.playingIntro && this.xPos < this.config.START_X_POS) {
+      this.xPos += Math.round((this.config.START_X_POS /
+          this.config.INTRO_DURATION) * deltaTime);
+    }
+
+    if (this.status == Trex.status.WAITING) {
+      this.blink(performance.now());
+    } else {
+      this.draw(this.currentAnimFrames[this.currentFrame], 0);
+    }
+
+    // Update the frame position.
+    if (this.timer >= this.msPerFrame) {
+      this.currentFrame = this.currentFrame ==
+          this.currentAnimFrames.length - 1 ? 0 : this.currentFrame + 1;
+      this.timer = 0;
+    }
+  },
+
+  /**
+   * Draw the t-rex to a particular position.
+   * @param {number} x
+   * @param {number} y
+   */
+  draw: function(x, y) {
+    var sourceX = x;
+    var sourceY = y;
+    var sourceWidth = this.config.WIDTH;
+    var sourceHeight = this.config.HEIGHT;
+
+    if (IS_HIDPI) {
+      sourceX *= 2;
+      sourceY *= 2;
+      sourceWidth *= 2;
+      sourceHeight *= 2;
+    }
+
+    this.canvasCtx.drawImage(this.image, sourceX, sourceY,
+        sourceWidth, sourceHeight,
+        this.xPos, this.yPos,
+        this.config.WIDTH, this.config.HEIGHT);
+  },
+
+  /**
+   * Sets a random time for the blink to happen.
+   */
+  setBlinkDelay: function() {
+    this.blinkDelay = Math.ceil(Math.random() * Trex.BLINK_TIMING);
+  },
+
+  /**
+   * Make t-rex blink at random intervals.
+   * @param {number} time Current time in milliseconds.
+   */
+  blink: function(time) {
+    var deltaTime = time - this.animStartTime;
+
+    if (deltaTime >= this.blinkDelay) {
+      this.draw(this.currentAnimFrames[this.currentFrame], 0);
+
+      if (this.currentFrame == 1) {
+        // Set new random delay to blink.
+        this.setBlinkDelay();
+        this.animStartTime = time;
+      }
+    }
+  },
+
+  /**
+   * Initialise a jump.
+   */
+  startJump: function() {
+    if (!this.jumping) {
+      this.update(0, Trex.status.JUMPING);
+      this.jumpVelocity = this.config.INIITAL_JUMP_VELOCITY;
+      this.jumping = true;
+      this.reachedMinHeight = false;
+      this.speedDrop = false;
+    }
+  },
+
+  /**
+   * Jump is complete, falling down.
+   */
+  endJump: function() {
+    if (this.reachedMinHeight &&
+        this.jumpVelocity < this.config.DROP_VELOCITY) {
+      this.jumpVelocity = this.config.DROP_VELOCITY;
+    }
+  },
+
+  /**
+   * Update frame for a jump.
+   * @param {number} deltaTime
+   */
+  updateJump: function(deltaTime) {
+    var msPerFrame = Trex.animFrames[this.status].msPerFrame;
+    var framesElapsed = deltaTime / msPerFrame;
+
+    // Speed drop makes Trex fall faster.
+    if (this.speedDrop) {
+      this.yPos += Math.round(this.jumpVelocity *
+          this.config.SPEED_DROP_COEFFICIENT * framesElapsed);
+    } else {
+      this.yPos += Math.round(this.jumpVelocity * framesElapsed);
+    }
+
+    this.jumpVelocity += this.config.GRAVITY * framesElapsed;
+
+    // Minimum height has been reached.
+    if (this.yPos < this.minJumpHeight || this.speedDrop) {
+      this.reachedMinHeight = true;
+    }
+
+    // Reached max height
+    if (this.yPos < this.config.MAX_JUMP_HEIGHT || this.speedDrop) {
+      this.endJump();
+    }
+
+    // Back down at ground level. Jump completed.
+    if (this.yPos > this.groundYPos) {
+      this.reset();
+      this.jumpCount++;
+    }
+
+    this.update(deltaTime);
+  },
+
+  /**
+   * Set the speed drop. Immediately cancels the current jump.
+   */
+  setSpeedDrop: function() {
+    this.speedDrop = true;
+    this.jumpVelocity = 1;
+  },
+
+  /**
+   * Reset the t-rex to running at start of game.
+   */
+  reset: function() {
+    this.yPos = this.groundYPos;
+    this.jumpVelocity = 0;
+    this.jumping = false;
+    this.update(0, Trex.status.RUNNING);
+    this.midair = false;
+    this.speedDrop = false;
+    this.jumpCount = 0;
+  }
+};
+
+
+//******************************************************************************
+
+/**
+ * Handles displaying the distance meter.
+ * @param {!HTMLCanvasElement} canvas
+ * @param {!HTMLImage} spriteSheet Image sprite.
+ * @param {number} canvasWidth
+ * @constructor
+ */
+function DistanceMeter(canvas, spriteSheet, canvasWidth) {
+  this.canvas = canvas;
+  this.canvasCtx = canvas.getContext('2d');
+  this.image = spriteSheet;
+  this.x = 0;
+  this.y = 5;
+
+  this.currentDistance = 0;
+  this.maxScore = 0;
+  this.highScore = 0;
+  this.container = null;
+
+  this.digits = [];
+  this.acheivement = false;
+  this.defaultString = '';
+  this.flashTimer = 0;
+  this.flashIterations = 0;
+
+  this.config = DistanceMeter.config;
+  this.init(canvasWidth);
+};
+
+
+/**
+ * @enum {number}
+ */
+DistanceMeter.dimensions = {
+  WIDTH: 10,
+  HEIGHT: 13,
+  DEST_WIDTH: 11
+};
+
+
+/**
+ * Y positioning of the digits in the sprite sheet.
+ * X position is always 0.
+ * @type {array.<number>}
+ */
+DistanceMeter.yPos = [0, 13, 27, 40, 53, 67, 80, 93, 107, 120];
+
+
+/**
+ * Distance meter config.
+ * @enum {number}
+ */
+DistanceMeter.config = {
+  // Number of digits.
+  MAX_DISTANCE_UNITS: 5,
+
+  // Distance that causes achievement animation.
+  ACHIEVEMENT_DISTANCE: 100,
+
+  // Used for conversion from pixel distance to a scaled unit.
+  COEFFICIENT: 0.025,
+
+  // Flash duration in milliseconds.
+  FLASH_DURATION: 1000 / 4,
+
+  // Flash iterations for achievement animation.
+  FLASH_ITERATIONS: 3
+};
+
+
+DistanceMeter.prototype = {
+  /**
+   * Initialise the distance meter to '00000'.
+   * @param {number} width Canvas width in px.
+   */
+  init: function(width) {
+    var maxDistanceStr = '';
+
+    this.calcXPos(width);
+    this.maxScore = this.config.MAX_DISTANCE_UNITS;
+    for (var i = 0; i < this.config.MAX_DISTANCE_UNITS; i++) {
+      this.draw(i, 0);
+      this.defaultString += '0';
+      maxDistanceStr += '9';
+    }
+
+    this.maxScore = parseInt(maxDistanceStr);
+  },
+
+  /**
+   * Calculate the xPos in the canvas.
+   * @param {number} canvasWidth
+   */
+  calcXPos: function(canvasWidth) {
+    this.x = canvasWidth - (DistanceMeter.dimensions.DEST_WIDTH *
+        (this.config.MAX_DISTANCE_UNITS + 1));
+  },
+
+  /**
+   * Draw a digit to canvas.
+   * @param {number} digitPos Position of the digit.
+   * @param {number} value Digit value 0-9.
+   * @param {boolean} opt_highScore Whether drawing the high score.
+   */
+  draw: function(digitPos, value, opt_highScore) {
+    var sourceWidth = DistanceMeter.dimensions.WIDTH;
+    var sourceHeight = DistanceMeter.dimensions.HEIGHT;
+    var sourceX = DistanceMeter.dimensions.WIDTH * value;
+
+    var targetX = digitPos * DistanceMeter.dimensions.DEST_WIDTH;
+    var targetY = this.y;
+    var targetWidth = DistanceMeter.dimensions.WIDTH;
+    var targetHeight = DistanceMeter.dimensions.HEIGHT;
+
+    // For high DPI we 2x source values.
+    if (IS_HIDPI) {
+      sourceWidth *= 2;
+      sourceHeight *= 2;
+      sourceX *= 2;
+    }
+
+    this.canvasCtx.save();
+
+    if (opt_highScore) {
+      // Left of the current score.
+      var highScoreX = this.x - (this.config.MAX_DISTANCE_UNITS * 2) *
+          DistanceMeter.dimensions.WIDTH;
+      this.canvasCtx.translate(highScoreX, this.y);
+    } else {
+      this.canvasCtx.translate(this.x, this.y);
+    }
+
+    this.canvasCtx.drawImage(this.image, sourceX, 0,
+        sourceWidth, sourceHeight,
+        targetX, targetY,
+        targetWidth, targetHeight
+      );
+
+    this.canvasCtx.restore();
+  },
+
+  /**
+   * Covert pixel distance to a 'real' distance.
+   * @param {number} distance Pixel distance ran.
+   * @return {number} The 'real' distance ran.
+   */
+  getActualDistance: function(distance) {
+    return distance ?
+        Math.round(distance * this.config.COEFFICIENT) : 0;
+  },
+
+  /**
+   * Update the distance meter.
+   * @param {number} deltaTime
+   * @param {number} distance
+   * @return {boolean} Whether the acheivement sound fx should be played.
+   */
+  update: function(deltaTime, distance) {
+    var paint = true;
+    var playSound = false;
+
+    if (!this.acheivement) {
+      distance = this.getActualDistance(distance);
+
+      if (distance > 0) {
+        // Acheivement unlocked
+        if (distance % this.config.ACHIEVEMENT_DISTANCE == 0) {
+          // Flash score and play sound.
+          this.acheivement = true;
+          this.flashTimer = 0;
+          playSound = true;
+        }
+
+        // Create a string representation of the distance with leading 0.
+        var distanceStr = (this.defaultString +
+            distance).substr(-this.config.MAX_DISTANCE_UNITS);
+        this.digits = distanceStr.split('');
+      } else {
+        this.digits = this.defaultString.split('');
+      }
+    } else {
+      // Control flashing of the score on reaching acheivement.
+      if (this.flashIterations <= this.config.FLASH_ITERATIONS) {
+        this.flashTimer += deltaTime;
+
+        if (this.flashTimer < this.config.FLASH_DURATION) {
+          paint = false;
+        } else if (this.flashTimer >
+            this.config.FLASH_DURATION * 2) {
+          this.flashTimer = 0;
+          this.flashIterations++;
+        }
+      } else {
+        this.acheivement = false;
+        this.flashIterations = 0;
+        this.flashTimer = 0;
+      }
+    }
+
+    // Draw the digits if not flashing.
+    if (paint) {
+      for (var i = this.digits.length - 1; i >= 0; i--) {
+        this.draw(i, parseInt(this.digits[i]));
+      }
+    }
+
+    this.drawHighScore();
+
+    return playSound;
+  },
+
+  /**
+   * Draw the high score.
+   */
+  drawHighScore: function() {
+    this.canvasCtx.save();
+    this.canvasCtx.globalAlpha = .8;
+    for (var i = this.highScore.length - 1; i >= 0; i--) {
+      this.draw(i, parseInt(this.highScore[i], 10), true);
+    }
+    this.canvasCtx.restore();
+  },
+
+  /**
+   * Set the highscore as a array string.
+   * Position of char in the sprite: H - 10, I - 11.
+   * @param {number} distance Distance ran in pixels.
+   */
+  setHighScore: function(distance) {
+    distance = this.getActualDistance(distance);
+    var highScoreStr = (this.defaultString +
+        distance).substr(-this.config.MAX_DISTANCE_UNITS);
+
+    this.highScore = ['10', '11', ''].concat(highScoreStr.split(''));
+  },
+
+  /**
+   * Reset the distance meter back to '00000'.
+   */
+  reset: function() {
+    this.update(0);
+    this.acheivement = false;
+  }
+};
+
+
+//******************************************************************************
+
+/**
+ * Cloud background item.
+ * Similar to an obstacle object but without collision boxes.
+ * @param {HTMLCanvasElement} canvas Canvas element.
+ * @param {Image} cloudImg
+ * @param {number} containerWidth
+ */
+function Cloud(canvas, cloudImg, containerWidth) {
+  this.canvas = canvas;
+  this.canvasCtx = this.canvas.getContext('2d');
+  this.image = cloudImg;
+  this.containerWidth = containerWidth;
+  this.xPos = containerWidth;
+  this.yPos = 0;
+  this.remove = false;
+  this.cloudGap = getRandomNum(Cloud.config.MIN_CLOUD_GAP,
+      Cloud.config.MAX_CLOUD_GAP);
+
+  this.init();
+};
+
+
+/**
+ * Cloud object config.
+ * @enum {number}
+ */
+Cloud.config = {
+  HEIGHT: 13,
+  MAX_CLOUD_GAP: 400,
+  MAX_SKY_LEVEL: 30,
+  MIN_CLOUD_GAP: 100,
+  MIN_SKY_LEVEL: 71,
+  WIDTH: 46
+};
+
+
+Cloud.prototype = {
+  /**
+   * Initialise the cloud. Sets the Cloud height.
+   */
+  init: function() {
+    this.yPos = getRandomNum(Cloud.config.MAX_SKY_LEVEL,
+        Cloud.config.MIN_SKY_LEVEL);
+    this.draw();
+  },
+
+  /**
+   * Draw the cloud.
+   */
+  draw: function() {
+    this.canvasCtx.save();
+    var sourceWidth = Cloud.config.WIDTH;
+    var sourceHeight = Cloud.config.HEIGHT;
+
+    if (IS_HIDPI) {
+      sourceWidth = sourceWidth * 2;
+      sourceHeight = sourceHeight * 2;
+    }
+
+    this.canvasCtx.drawImage(this.image, 0, 0,
+        sourceWidth, sourceHeight,
+        this.xPos, this.yPos,
+        Cloud.config.WIDTH, Cloud.config.HEIGHT);
+
+    this.canvasCtx.restore();
+  },
+
+  /**
+   * Update the cloud position.
+   * @param {number} speed
+   */
+  update: function(speed) {
+    if (!this.remove) {
+      this.xPos -= Math.ceil(speed);
+      this.draw();
+
+      // Mark as removeable if no longer in the canvas.
+      if (!this.isVisible()) {
+        this.remove = true;
+      }
+    }
+  },
+
+  /**
+   * Check if the cloud is visible on the stage.
+   * @return {boolean}
+   */
+  isVisible: function() {
+    return this.xPos + Cloud.config.WIDTH > 0;
+  }
+};
+
+
+//******************************************************************************
+
+/**
+ * Horizon Line.
+ * Consists of two connecting lines. Randomly assigns a flat / bumpy horizon.
+ * @param {HTMLCanvasElement} canvas
+ * @param {HTMLImage} bgImg Horizon line sprite.
+ * @constructor
+ */
+function HorizonLine(canvas, bgImg) {
+  this.image = bgImg;
+  this.canvas = canvas;
+  this.canvasCtx = canvas.getContext('2d');
+  this.sourceDimensions = {};
+  this.dimensions = HorizonLine.dimensions;
+  this.sourceXPos = [0, this.dimensions.WIDTH];
+  this.xPos = [];
+  this.yPos = 0;
+  this.bumpThreshold = 0.5;
+
+  this.setSourceDimensions();
+  this.draw();
+};
+
+
+/**
+ * Horizon line dimensions.
+ * @enum {number}
+ */
+HorizonLine.dimensions = {
+  WIDTH: 600,
+  HEIGHT: 12,
+  YPOS: 127
+};
+
+
+HorizonLine.prototype = {
+  /**
+   * Set the source dimensions of the horizon line.
+   */
+  setSourceDimensions: function() {
+
+    for (var dimension in HorizonLine.dimensions) {
+      if (IS_HIDPI) {
+        if (dimension != 'YPOS') {
+          this.sourceDimensions[dimension] =
+              HorizonLine.dimensions[dimension] * 2;
+        }
+      } else {
+        this.sourceDimensions[dimension] =
+            HorizonLine.dimensions[dimension];
+      }
+      this.dimensions[dimension] = HorizonLine.dimensions[dimension];
+    }
+
+    this.xPos = [0, HorizonLine.dimensions.WIDTH];
+    this.yPos = HorizonLine.dimensions.YPOS;
+  },
+
+  /**
+   * Return the crop x position of a type.
+   */
+  getRandomType: function() {
+    return Math.random() > this.bumpThreshold ? this.dimensions.WIDTH : 0;
+  },
+
+  /**
+   * Draw the horizon line.
+   */
+  draw: function() {
+    this.canvasCtx.drawImage(this.image, this.sourceXPos[0], 0,
+        this.sourceDimensions.WIDTH, this.sourceDimensions.HEIGHT,
+        this.xPos[0], this.yPos,
+        this.dimensions.WIDTH, this.dimensions.HEIGHT);
+
+    this.canvasCtx.drawImage(this.image, this.sourceXPos[1], 0,
+        this.sourceDimensions.WIDTH, this.sourceDimensions.HEIGHT,
+        this.xPos[1], this.yPos,
+        this.dimensions.WIDTH, this.dimensions.HEIGHT);
+  },
+
+  /**
+   * Update the x position of an indivdual piece of the line.
+   * @param {number} pos Line position.
+   * @param {number} increment
+   */
+  updateXPos: function(pos, increment) {
+    var line1 = pos;
+    var line2 = pos == 0 ? 1 : 0;
+
+    this.xPos[line1] -= increment;
+    this.xPos[line2] = this.xPos[line1] + this.dimensions.WIDTH;
+
+    if (this.xPos[line1] <= -this.dimensions.WIDTH) {
+      this.xPos[line1] += this.dimensions.WIDTH * 2;
+      this.xPos[line2] = this.xPos[line1] - this.dimensions.WIDTH;
+      this.sourceXPos[line1] = this.getRandomType();
+    }
+  },
+
+  /**
+   * Update the horizon line.
+   * @param {number} deltaTime
+   * @param {number} speed
+   */
+  update: function(deltaTime, speed) {
+    var increment = Math.floor(speed * (FPS / 1000) * deltaTime);
+
+    if (this.xPos[0] <= 0) {
+      this.updateXPos(0, increment);
+    } else {
+      this.updateXPos(1, increment);
+    }
+    this.draw();
+  },
+
+  /**
+   * Reset horizon to the starting position.
+   */
+  reset: function() {
+    this.xPos[0] = 0;
+    this.xPos[1] = HorizonLine.dimensions.WIDTH;
+  }
+};
+
+
+//******************************************************************************
+
+/**
+ * Horizon background class.
+ * @param {HTMLCanvasElement} canvas
+ * @param {Array.<HTMLImageElement>} images
+ * @param {object} dimensions Canvas dimensions.
+ * @param {number} gapCoefficient
+ * @constructor
+ */
+function Horizon(canvas, images, dimensions, gapCoefficient) {
+  this.canvas = canvas;
+  this.canvasCtx = this.canvas.getContext('2d');
+  this.config = Horizon.config;
+  this.dimensions = dimensions;
+  this.gapCoefficient = gapCoefficient;
+  this.obstacles = [];
+  this.horizonOffsets = [0, 0];
+  this.cloudFrequency = this.config.CLOUD_FREQUENCY;
+
+  // Cloud
+  this.clouds = [];
+  this.cloudImg = images.CLOUD;
+  this.cloudSpeed = this.config.BG_CLOUD_SPEED;
+
+  // Horizon
+  this.horizonImg = images.HORIZON;
+  this.horizonLine = null;
+
+  // Obstacles
+  this.obstacleImgs = {
+    CACTUS_SMALL: images.CACTUS_SMALL,
+    CACTUS_LARGE: images.CACTUS_LARGE
+  };
+
+  this.init();
+};
+
+
+/**
+ * Horizon config.
+ * @enum {number}
+ */
+Horizon.config = {
+  BG_CLOUD_SPEED: 0.2,
+  BUMPY_THRESHOLD: .3,
+  CLOUD_FREQUENCY: .5,
+  HORIZON_HEIGHT: 16,
+  MAX_CLOUDS: 6
+};
+
+
+Horizon.prototype = {
+  /**
+   * Initialise the horizon. Just add the line and a cloud. No obstacles.
+   */
+  init: function() {
+    this.addCloud();
+    this.horizonLine = new HorizonLine(this.canvas, this.horizonImg);
+  },
+
+  /**
+   * @param {number} deltaTime
+   * @param {number} currentSpeed
+   * @param {boolean} updateObstacles Used as an override to prevent
+   *     the obstacles from being updated / added. This happens in the
+   *     ease in section.
+   */
+  update: function(deltaTime, currentSpeed, updateObstacles) {
+    this.runningTime += deltaTime;
+    this.horizonLine.update(deltaTime, currentSpeed);
+    this.updateClouds(deltaTime, currentSpeed);
+
+    if (updateObstacles) {
+      this.updateObstacles(deltaTime, currentSpeed);
+    }
+  },
+
+  /**
+   * Update the cloud positions.
+   * @param {number} deltaTime
+   * @param {number} currentSpeed
+   */
+  updateClouds: function(deltaTime, speed) {
+    var cloudSpeed = this.cloudSpeed / 1000 * deltaTime * speed;
+    var numClouds = this.clouds.length;
+
+    if (numClouds) {
+      for (var i = numClouds - 1; i >= 0; i--) {
+        this.clouds[i].update(cloudSpeed);
+      }
+
+      var lastCloud = this.clouds[numClouds - 1];
+
+      // Check for adding a new cloud.
+      if (numClouds < this.config.MAX_CLOUDS &&
+          (this.dimensions.WIDTH - lastCloud.xPos) > lastCloud.cloudGap &&
+          this.cloudFrequency > Math.random()) {
+        this.addCloud();
+      }
+
+      // Remove expired clouds.
+      this.clouds = this.clouds.filter(function(obj) {
+        return !obj.remove;
+      });
+    }
+  },
+
+  /**
+   * Update the obstacle positions.
+   * @param {number} deltaTime
+   * @param {number} currentSpeed
+   */
+  updateObstacles: function(deltaTime, currentSpeed) {
+    // Obstacles, move to Horizon layer.
+    var updatedObstacles = this.obstacles.slice(0);
+
+    for (var i = 0; i < this.obstacles.length; i++) {
+      var obstacle = this.obstacles[i];
+      obstacle.update(deltaTime, currentSpeed);
+
+      // Clean up existing obstacles.
+      if (obstacle.remove) {
+        updatedObstacles.shift();
+      }
+    }
+    this.obstacles = updatedObstacles;
+
+    if (this.obstacles.length > 0) {
+      var lastObstacle = this.obstacles[this.obstacles.length - 1];
+
+      if (lastObstacle && !lastObstacle.followingObstacleCreated &&
+          lastObstacle.isVisible() &&
+          (lastObstacle.xPos + lastObstacle.width + lastObstacle.gap) <
+          this.dimensions.WIDTH) {
+        this.addNewObstacle(currentSpeed);
+        lastObstacle.followingObstacleCreated = true;
+      }
+    } else {
+      // Create new obstacles.
+      this.addNewObstacle(currentSpeed);
+    }
+  },
+
+  /**
+   * Add a new obstacle.
+   * @param {number} currentSpeed
+   */
+  addNewObstacle: function(currentSpeed) {
+    var obstacleTypeIndex =
+        getRandomNum(0, Obstacle.types.length - 1);
+    var obstacleType = Obstacle.types[obstacleTypeIndex];
+    var obstacleImg = this.obstacleImgs[obstacleType.type];
+
+    this.obstacles.push(new Obstacle(this.canvasCtx, obstacleType,
+        obstacleImg, this.dimensions, this.gapCoefficient, currentSpeed));
+  },
+
+  /**
+   * Reset the horizon layer.
+   * Remove existing obstacles and reposition the horizon line.
+   */
+  reset: function() {
+    this.obstacles = [];
+    this.horizonLine.reset();
+  },
+
+  /**
+   * Update the canvas width and scaling.
+   * @param {number} width Canvas width.
+   * @param {number} height Canvas height.
+   */
+  resize: function(width, height) {
+    this.canvas.width = width;
+    this.canvas.height = height;
+  },
+
+  /**
+   * Add a new cloud to the horizon.
+   */
+  addCloud: function() {
+    this.clouds.push(new Cloud(this.canvas, this.cloudImg,
+        this.dimensions.WIDTH));
+  }
+};
+})();