src/tools/telemetry/telemetry/page/actions/scroll.js

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // This file provides the ScrollAction object, which scrolls a page
   6 // from top to bottom:
   7 //   1. var action = new __ScrollAction(callback)
   8 //   2. action.start(scroll_options)
   9 'use strict';
  10
  11 (function() {
  12   var MAX_SCROLL_LENGTH_PIXELS = 5000;
  13
  14   function ScrollGestureOptions(opt_options) {
  15     if (opt_options) {
  16       this.element_ = opt_options.element;
  17       this.left_start_percentage_ = opt_options.left_start_percentage;
  18       this.top_start_percentage_ = opt_options.top_start_percentage;
  19     } else {
  20       this.element_ = document.body;
  21       this.left_start_percentage_ = 0.5;
  22       this.top_start_percentage_ = 0.5;
  23     }
  24   }
  25
  26   function supportedByBrowser() {
  27     return !!(window.chrome &&
  28               chrome.gpuBenchmarking &&
  29               chrome.gpuBenchmarking.smoothScrollBy);
  30   }
  31
  32   /**
  33    * Scrolls a given element down a certain amount to emulate user scroll.
  34    * Uses smooth scroll capabilities provided by the platform, if available.
  35    * @constructor
  36    */
  37   function SmoothScrollDownGesture(options) {
  38     this.options_ = options;
  39   };
  40
  41   function min(a, b) {
  42     if (a > b) {
  43       return b;
  44     }
  45     return a;
  46   };
  47
  48   function getBoundingVisibleRect(el) {
  49     var bound = el.getBoundingClientRect();
  50     var rect = { top: bound.top,
  51                  left: bound.left,
  52                  width: bound.width,
  53                  height: bound.height };
  54     var outsideHeight = (rect.top + rect.height) - window.innerHeight;
  55     var outsideWidth = (rect.left + rect.width) - window.innerWidth;
  56
  57     if (outsideHeight > 0) {
  58       rect.height -= outsideHeight;
  59     }
  60     if (outsideWidth > 0) {
  61       rect.width -= outsideWidth;
  62     }
  63     return rect;
  64   };
  65
  66   SmoothScrollDownGesture.prototype.start = function(distance, callback) {
  67     this.callback_ = callback;
  68
  69     var rect = getBoundingVisibleRect(this.options_.element_);
  70     var start_left =
  71         rect.left + rect.width * this.options_.left_start_percentage_;
  72     var start_top =
  73         rect.top + rect.height * this.options_.top_start_percentage_;
  74     chrome.gpuBenchmarking.smoothScrollBy(distance, function() {
  75       callback();
  76     }, start_left, start_top);
  77   };
  78
  79   // This class scrolls a page from the top to the bottom once.
  80   //
  81   // The page is scrolled down by a single scroll gesture.
  82   function ScrollAction(opt_callback, opt_remaining_distance_func) {
  83     var self = this;
  84
  85     this.beginMeasuringHook = function() {}
  86     this.endMeasuringHook = function() {}
  87
  88     this.callback_ = opt_callback;
  89     this.remaining_distance_func_ = opt_remaining_distance_func;
  90   }
  91
  92   ScrollAction.prototype.getRemainingScrollDistance_ = function() {
  93     if (this.remaining_distance_func_)
  94       return this.remaining_distance_func_();
  95
  96     var clientHeight;
  97     // clientHeight is "special" for the body element.
  98     if (this.element_ == document.body)
  99       clientHeight = window.innerHeight;
 100     else
 101       clientHeight = this.element_.clientHeight;
 102
 103     return this.scrollHeight_ - this.element_.scrollTop - clientHeight;
 104   }
 105
 106   ScrollAction.prototype.start = function(opt_options) {
 107     this.options_ = new ScrollGestureOptions(opt_options);
 108     // Assign this.element_ here instead of constructor, because the constructor
 109     // ensures this method will be called after the document is loaded.
 110     this.element_ = this.options_.element_;
 111     // Some pages load more content when you scroll to the bottom. Record
 112     // the original element height here and only scroll to that point.
 113     // -1 to allow for rounding errors on scaled viewports (like mobile).
 114     this.scrollHeight_ = Math.min(MAX_SCROLL_LENGTH_PIXELS,
 115                                   this.element_.scrollHeight - 1);
 116     requestAnimationFrame(this.startPass_.bind(this));
 117   };
 118
 119   ScrollAction.prototype.startPass_ = function() {
 120     this.element_.scrollTop = 0;
 121
 122     this.beginMeasuringHook();
 123
 124     this.gesture_ = new SmoothScrollDownGesture(this.options_);
 125     this.gesture_.start(this.getRemainingScrollDistance_(),
 126                         this.onGestureComplete_.bind(this));
 127   };
 128
 129   ScrollAction.prototype.onGestureComplete_ = function() {
 130     this.endMeasuringHook();
 131
 132     // We're done.
 133     if (this.callback_)
 134       this.callback_();
 135   };
 136
 137   window.__ScrollAction = ScrollAction;
 138   window.__ScrollAction_GetBoundingVisibleRect = getBoundingVisibleRect;
 139   window.__ScrollAction_SupportedByBrowser = supportedByBrowser;
 140 })();