text: /**
   * @license
   * Visual Blocks Editor
   *
   * Copyright 2011 Google Inc.
   * https://developers.google.com/blockly/
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  /**
   * @fileoverview Library for creating scrollbars.
   * @author fraser@google.com (Neil Fraser)
   */
  'use strict';
  
  goog.provide('Blockly.Scrollbar');
  goog.provide('Blockly.ScrollbarPair');
  
  goog.require('goog.dom');
  goog.require('goog.events');
  
  
  /**
   * Class for a pair of scrollbars.  Horizontal and vertical.
   * @param {!Blockly.Workspace} workspace Workspace to bind the scrollbars to.
   * @constructor
   */
  Blockly.ScrollbarPair = function(workspace) {
    this.workspace_ = workspace;
    this.hScroll = new Blockly.Scrollbar(workspace, true, true);
    this.vScroll = new Blockly.Scrollbar(workspace, false, true);
    this.corner_ = Blockly.createSvgElement('rect',
        {'height': Blockly.Scrollbar.scrollbarThickness,
        'width': Blockly.Scrollbar.scrollbarThickness,
        'class': 'blocklyScrollbarBackground'}, null);
    Blockly.Scrollbar.insertAfter_(this.corner_, workspace.getBubbleCanvas());
  };
  
  /**
   * Previously recorded metrics from the workspace.
   * @type {Object}
   * @private
   */
  Blockly.ScrollbarPair.prototype.oldHostMetrics_ = null;
  
  /**
   * Dispose of this pair of scrollbars.
   * Unlink from all DOM elements to prevent memory leaks.
   */
  Blockly.ScrollbarPair.prototype.dispose = function() {
    goog.dom.removeNode(this.corner_);
    this.corner_ = null;
    this.workspace_ = null;
    this.oldHostMetrics_ = null;
    this.hScroll.dispose();
    this.hScroll = null;
    this.vScroll.dispose();
    this.vScroll = null;
  };
  
  /**
   * Recalculate both of the scrollbars' locations and lengths.
   * Also reposition the corner rectangle.
   */
  Blockly.ScrollbarPair.prototype.resize = function() {
    // Look up the host metrics once, and use for both scrollbars.
    var hostMetrics = this.workspace_.getMetrics();
    if (!hostMetrics) {
      // Host element is likely not visible.
      return;
    }
  
    // Only change the scrollbars if there has been a change in metrics.
    var resizeH = false;
    var resizeV = false;
    if (!this.oldHostMetrics_ ||
        this.oldHostMetrics_.viewWidth != hostMetrics.viewWidth ||
        this.oldHostMetrics_.viewHeight != hostMetrics.viewHeight ||
        this.oldHostMetrics_.absoluteTop != hostMetrics.absoluteTop ||
        this.oldHostMetrics_.absoluteLeft != hostMetrics.absoluteLeft) {
      // The window has been resized or repositioned.
      resizeH = true;
      resizeV = true;
    } else {
      // Has the content been resized or moved?
      if (!this.oldHostMetrics_ ||
          this.oldHostMetrics_.contentWidth != hostMetrics.contentWidth ||
          this.oldHostMetrics_.viewLeft != hostMetrics.viewLeft ||
          this.oldHostMetrics_.contentLeft != hostMetrics.contentLeft) {
        resizeH = true;
      }
      if (!this.oldHostMetrics_ ||
          this.oldHostMetrics_.contentHeight != hostMetrics.contentHeight ||
          this.oldHostMetrics_.viewTop != hostMetrics.viewTop ||
          this.oldHostMetrics_.contentTop != hostMetrics.contentTop) {
        resizeV = true;
      }
    }
    if (resizeH) {
      this.hScroll.resize(hostMetrics);
    }
    if (resizeV) {
      this.vScroll.resize(hostMetrics);
    }
  
    // Reposition the corner square.
    if (!this.oldHostMetrics_ ||
        this.oldHostMetrics_.viewWidth != hostMetrics.viewWidth ||
        this.oldHostMetrics_.absoluteLeft != hostMetrics.absoluteLeft) {
      this.corner_.setAttribute('x', this.vScroll.position_.x);
    }
    if (!this.oldHostMetrics_ ||
        this.oldHostMetrics_.viewHeight != hostMetrics.viewHeight ||
        this.oldHostMetrics_.absoluteTop != hostMetrics.absoluteTop) {
      this.corner_.setAttribute('y', this.hScroll.position_.y);
    }
  
    // Cache the current metrics to potentially short-cut the next resize event.
    this.oldHostMetrics_ = hostMetrics;
  };
  
  /**
   * Set the sliders of both scrollbars to be at a certain position.
   * @param {number} x Horizontal scroll value.
   * @param {number} y Vertical scroll value.
   */
  Blockly.ScrollbarPair.prototype.set = function(x, y) {
    // This function is equivalent to:
    //   this.hScroll.set(x);
    //   this.vScroll.set(y);
    // However, that calls setMetrics twice which causes a chain of
    // getAttribute->setAttribute->getAttribute resulting in an extra layout pass.
    // Combining them speeds up rendering.
    var xyRatio = {};
  
    var hHandlePosition = x * this.hScroll.ratio_;
    var vHandlePosition = y * this.vScroll.ratio_;
  
    var hBarLength = this.hScroll.scrollViewSize_;
    var vBarLength = this.vScroll.scrollViewSize_;
  
    xyRatio.x = this.getRatio_(hHandlePosition, hBarLength);
    xyRatio.y = this.getRatio_(vHandlePosition, vBarLength);
    this.workspace_.setMetrics(xyRatio);
  
    this.hScroll.setHandlePosition(hHandlePosition);
    this.vScroll.setHandlePosition(vHandlePosition);
  };
  
  /**
   * Helper to calculate the ratio of handle position to scrollbar view size.
   * @param {number} handlePosition The value of the handle.
   * @param {number} viewSize The total size of the scrollbar's view.
   * @return {number} Ratio.
   * @private
   */
  Blockly.ScrollbarPair.prototype.getRatio_ = function(handlePosition, viewSize) {
    var ratio = handlePosition / viewSize;
    if (isNaN(ratio)) {
      return 0;
    }
    return ratio;
  };
  
  // --------------------------------------------------------------------
  
  /**
   * Class for a pure SVG scrollbar.
   * This technique offers a scrollbar that is guaranteed to work, but may not
   * look or behave like the system's scrollbars.
   * @param {!Blockly.Workspace} workspace Workspace to bind the scrollbar to.
   * @param {boolean} horizontal True if horizontal, false if vertical.
   * @param {boolean=} opt_pair True if scrollbar is part of a horiz/vert pair.
   * @constructor
   */
  Blockly.Scrollbar = function(workspace, horizontal, opt_pair) {
    this.workspace_ = workspace;
    this.pair_ = opt_pair || false;
    this.horizontal_ = horizontal;
    this.oldHostMetrics_ = null;
  
    this.createDom_();
  
    /**
     * The upper left corner of the scrollbar's svg group.
     * @type {goog.math.Coordinate}
     * @private
     */
    this.position_ = new goog.math.Coordinate(0, 0);
  
    if (horizontal) {
      this.svgBackground_.setAttribute('height',
          Blockly.Scrollbar.scrollbarThickness);
      this.svgHandle_.setAttribute('height',
          Blockly.Scrollbar.scrollbarThickness - 5);
      this.svgHandle_.setAttribute('y', 2.5);
  
      this.lengthAttribute_ = 'width';
      this.positionAttribute_ = 'x';
    } else {
      this.svgBackground_.setAttribute('width',
          Blockly.Scrollbar.scrollbarThickness);
      this.svgHandle_.setAttribute('width',
          Blockly.Scrollbar.scrollbarThickness - 5);
      this.svgHandle_.setAttribute('x', 2.5);
  
      this.lengthAttribute_ = 'height';
      this.positionAttribute_ = 'y';
    }
    var scrollbar = this;
    this.onMouseDownBarWrapper_ = Blockly.bindEventWithChecks_(
        this.svgBackground_, 'mousedown', scrollbar, scrollbar.onMouseDownBar_);
    this.onMouseDownHandleWrapper_ = Blockly.bindEventWithChecks_(this.svgHandle_,
        'mousedown', scrollbar, scrollbar.onMouseDownHandle_);
  };
  
  /**
   * The size of the area within which the scrollbar handle can move.
   * @type {number}
   * @private
   */
  Blockly.Scrollbar.prototype.scrollViewSize_ = 0;
  
  /**
   * The length of the scrollbar handle.
   * @type {number}
   * @private
   */
  Blockly.Scrollbar.prototype.handleLength_ = 0;
  
  /**
   * The offset of the start of the handle from the start of the scrollbar range.
   * @type {number}
   * @private
   */
  Blockly.Scrollbar.prototype.handlePosition_ = 0;
  
  /**
   * Whether the scrollbar handle is visible.
   * @type {boolean}
   * @private
   */
  Blockly.Scrollbar.prototype.isVisible_ = true;
  
  /**
   * Width of vertical scrollbar or height of horizontal scrollbar.
   * Increase the size of scrollbars on touch devices.
   * Don't define if there is no document object (e.g. node.js).
   */
  Blockly.Scrollbar.scrollbarThickness = 15;
  if (goog.events.BrowserFeature.TOUCH_ENABLED) {
    Blockly.Scrollbar.scrollbarThickness = 25;
  }
  
  /**
   * @param {!Object} first An object containing computed measurements of a
   *    workspace.
   * @param {!Object} second Another object containing computed measurements of a
   *    workspace.
   * @return {boolean} Whether the two sets of metrics are equivalent.
   * @private
   */
  Blockly.Scrollbar.metricsAreEquivalent_ = function(first, second) {
    if (!(first && second)) {
      return false;
    }
  
    if (first.viewWidth != second.viewWidth ||
        first.viewHeight != second.viewHeight ||
        first.viewLeft != second.viewLeft ||
        first.viewTop != second.viewTop ||
        first.absoluteTop != second.absoluteTop ||
        first.absoluteLeft != second.absoluteLeft ||
        first.contentWidth != second.contentWidth ||
        first.contentHeight != second.contentHeight ||
        first.contentLeft != second.contentLeft ||
        first.contentTop != second.contentTop) {
      return false;
    }
  
    return true;
  };
  
  /**
   * Dispose of this scrollbar.
   * Unlink from all DOM elements to prevent memory leaks.
   */
  Blockly.Scrollbar.prototype.dispose = function() {
    this.cleanUp_();
    Blockly.unbindEvent_(this.onMouseDownBarWrapper_);
    this.onMouseDownBarWrapper_ = null;
    Blockly.unbindEvent_(this.onMouseDownHandleWrapper_);
    this.onMouseDownHandleWrapper_ = null;
  
    goog.dom.removeNode(this.svgGroup_);
    this.svgGroup_ = null;
    this.svgBackground_ = null;
    this.svgHandle_ = null;
    this.workspace_ = null;
  };
  
  /**
   * Set the length of the scrollbar's handle and change the SVG attribute
   * accordingly.
   * @param {number} newLength The new scrollbar handle length.
   */
  Blockly.Scrollbar.prototype.setHandleLength_ = function(newLength) {
    this.handleLength_ = newLength;
    this.svgHandle_.setAttribute(this.lengthAttribute_, this.handleLength_);
  };
  
  /**
   * Set the offset of the scrollbar's handle and change the SVG attribute
   * accordingly.
   * @param {number} newPosition The new scrollbar handle offset.
   */
  Blockly.Scrollbar.prototype.setHandlePosition = function(newPosition) {
    this.handlePosition_ = newPosition;
    this.svgHandle_.setAttribute(this.positionAttribute_, this.handlePosition_);
  };
  
  /**
   * Set the size of the scrollbar's background and change the SVG attribute
   * accordingly.
   * @param {number} newSize The new scrollbar background length.
   * @private
   */
  Blockly.Scrollbar.prototype.setScrollViewSize_ = function(newSize) {
    this.scrollViewSize_ = newSize;
    this.svgBackground_.setAttribute(this.lengthAttribute_, this.scrollViewSize_);
  };
  
  /**
   * Set the position of the scrollbar's svg group.
   * @param {number} x The new x coordinate.
   * @param {number} y The new y coordinate.
   */
  Blockly.Scrollbar.prototype.setPosition = function(x, y) {
    this.position_.x = x;
    this.position_.y = y;
  
    this.svgGroup_.setAttribute('transform',
        'translate(' + this.position_.x + ',' + this.position_.y + ')');
  };
  
  /**
   * Recalculate the scrollbar's location and its length.
   * @param {Object=} opt_metrics A data structure of from the describing all the
   * required dimensions.  If not provided, it will be fetched from the host
   * object.
   */
  Blockly.Scrollbar.prototype.resize = function(opt_metrics) {
    // Determine the location, height and width of the host element.
    var hostMetrics = opt_metrics;
    if (!hostMetrics) {
      hostMetrics = this.workspace_.getMetrics();
      if (!hostMetrics) {
        // Host element is likely not visible.
        return;
      }
    }
  
    if (Blockly.Scrollbar.metricsAreEquivalent_(hostMetrics,
        this.oldHostMetrics_)) {
      return;
    }
    this.oldHostMetrics_ = hostMetrics;
  
    /* hostMetrics is an object with the following properties.
     * .viewHeight: Height of the visible rectangle,
     * .viewWidth: Width of the visible rectangle,
     * .contentHeight: Height of the contents,
     * .contentWidth: Width of the content,
     * .viewTop: Offset of top edge of visible rectangle from parent,
     * .viewLeft: Offset of left edge of visible rectangle from parent,
     * .contentTop: Offset of the top-most content from the y=0 coordinate,
     * .contentLeft: Offset of the left-most content from the x=0 coordinate,
     * .absoluteTop: Top-edge of view.
     * .absoluteLeft: Left-edge of view.
     */
    if (this.horizontal_) {
      this.resizeHorizontal_(hostMetrics);
    } else {
      this.resizeVertical_(hostMetrics);
    }
    // Resizing may have caused some scrolling.
    this.onScroll_();
  };
  
  /**
   * Recalculate a horizontal scrollbar's location and length.
   * @param {!Object} hostMetrics A data structure describing all the
   *     required dimensions, possibly fetched from the host object.
   * @private
   */
  Blockly.Scrollbar.prototype.resizeHorizontal_ = function(hostMetrics) {
    // TODO: Inspect metrics to determine if we can get away with just a content
    // resize.
    this.resizeViewHorizontal(hostMetrics);
  };
  
  /**
   * Recalculate a horizontal scrollbar's location on the screen and path length.
   * This should be called when the layout or size of the window has changed.
   * @param {!Object} hostMetrics A data structure describing all the
   *     required dimensions, possibly fetched from the host object.
   */
  Blockly.Scrollbar.prototype.resizeViewHorizontal = function(hostMetrics) {
    var viewSize = hostMetrics.viewWidth - 1;
    if (this.pair_) {
      // Shorten the scrollbar to make room for the corner square.
      viewSize -= Blockly.Scrollbar.scrollbarThickness;
    }
    this.setScrollViewSize_(Math.max(0, viewSize));
  
    var xCoordinate = hostMetrics.absoluteLeft + 0.5;
    if (this.pair_ && this.workspace_.RTL) {
      xCoordinate += Blockly.Scrollbar.scrollbarThickness;
    }
  
    // Horizontal toolbar should always be just above the bottom of the workspace.
    var yCoordinate = hostMetrics.absoluteTop + hostMetrics.viewHeight -
        Blockly.Scrollbar.scrollbarThickness - 0.5;
    this.setPosition(xCoordinate, yCoordinate);
  
    // If the view has been resized, a content resize will also be necessary.  The
    // reverse is not true.
    this.resizeContentHorizontal(hostMetrics);
  };
  
  /**
   * Recalculate a horizontal scrollbar's location within its path and length.
   * This should be called when the contents of the workspace have changed.
   * @param {!Object} hostMetrics A data structure describing all the
   *     required dimensions, possibly fetched from the host object.
   */
  Blockly.Scrollbar.prototype.resizeContentHorizontal = function(hostMetrics) {
    if (!this.pair_) {
      // Only show the scrollbar if needed.
      // Ideally this would also apply to scrollbar pairs, but that's a bigger
      // headache (due to interactions with the corner square).
      this.setVisible(this.scrollViewSize_ < hostMetrics.contentWidth);
    }
  
    this.ratio_ = this.scrollViewSize_ / hostMetrics.contentWidth;
    if (this.ratio_ == -Infinity || this.ratio_ == Infinity ||
        isNaN(this.ratio_)) {
      this.ratio_ = 0;
    }
  
    var handleLength = hostMetrics.viewWidth * this.ratio_;
    this.setHandleLength_(Math.max(0, handleLength));
  
    var handlePosition = (hostMetrics.viewLeft - hostMetrics.contentLeft) *
        this.ratio_;
    this.setHandlePosition(this.constrainHandle_(handlePosition));
  };
  
  /**
   * Recalculate a vertical scrollbar's location and length.
   * @param {!Object} hostMetrics A data structure describing all the
   *     required dimensions, possibly fetched from the host object.
   * @private
   */
  Blockly.Scrollbar.prototype.resizeVertical_ = function(hostMetrics) {
    // TODO: Inspect metrics to determine if we can get away with just a content
    // resize.
    this.resizeViewVertical(hostMetrics);
  };
  
  /**
   * Recalculate a vertical scrollbar's location on the screen and path length.
   * This should be called when the layout or size of the window has changed.
   * @param {!Object} hostMetrics A data structure describing all the
   *     required dimensions, possibly fetched from the host object.
   */
  Blockly.Scrollbar.prototype.resizeViewVertical = function(hostMetrics) {
    var viewSize = hostMetrics.viewHeight - 1;
    if (this.pair_) {
      // Shorten the scrollbar to make room for the corner square.
      viewSize -= Blockly.Scrollbar.scrollbarThickness;
    }
    this.setScrollViewSize_(Math.max(0, viewSize));
  
    var xCoordinate = hostMetrics.absoluteLeft + 0.5;
    if (!this.workspace_.RTL) {
      xCoordinate += hostMetrics.viewWidth -
          Blockly.Scrollbar.scrollbarThickness - 1;
    }
    var yCoordinate = hostMetrics.absoluteTop + 0.5;
    this.setPosition(xCoordinate, yCoordinate);
  
    // If the view has been resized, a content resize will also be necessary.  The
    // reverse is not true.
    this.resizeContentVertical(hostMetrics);
  };
  
  /**
   * Recalculate a vertical scrollbar's location within its path and length.
   * This should be called when the contents of the workspace have changed.
   * @param {!Object} hostMetrics A data structure describing all the
   *     required dimensions, possibly fetched from the host object.
   */
  Blockly.Scrollbar.prototype.resizeContentVertical = function(hostMetrics) {
    if (!this.pair_) {
      // Only show the scrollbar if needed.
      this.setVisible(this.scrollViewSize_ < hostMetrics.contentHeight);
    }
  
    this.ratio_ = this.scrollViewSize_ / hostMetrics.contentHeight;
    if (this.ratio_ == -Infinity || this.ratio_ == Infinity ||
        isNaN(this.ratio_)) {
      this.ratio_ = 0;
    }
  
    var handleLength = hostMetrics.viewHeight * this.ratio_;
    this.setHandleLength_(Math.max(0, handleLength));
  
    var handlePosition = (hostMetrics.viewTop - hostMetrics.contentTop) *
        this.ratio_;
    this.setHandlePosition(this.constrainHandle_(handlePosition));
  };
  
  /**
   * Create all the DOM elements required for a scrollbar.
   * The resulting widget is not sized.
   * @private
   */
  Blockly.Scrollbar.prototype.createDom_ = function() {
    /* Create the following DOM:
    <g class="blocklyScrollbarHorizontal">
      <rect class="blocklyScrollbarBackground" />
      <rect class="blocklyScrollbarHandle" rx="8" ry="8" />
    </g>
    */
    var className = 'blocklyScrollbar' +
        (this.horizontal_ ? 'Horizontal' : 'Vertical');
    this.svgGroup_ = Blockly.createSvgElement('g', {'class': className}, null);
    this.svgBackground_ = Blockly.createSvgElement('rect',
        {'class': 'blocklyScrollbarBackground'}, this.svgGroup_);
    var radius = Math.floor((Blockly.Scrollbar.scrollbarThickness - 5) / 2);
    this.svgHandle_ = Blockly.createSvgElement('rect',
        {'class': 'blocklyScrollbarHandle', 'rx': radius, 'ry': radius},
        this.svgGroup_);
    Blockly.Scrollbar.insertAfter_(this.svgGroup_,
                                   this.workspace_.getBubbleCanvas());
  };
  
  /**
   * Is the scrollbar visible.  Non-paired scrollbars disappear when they aren't
   * needed.
   * @return {boolean} True if visible.
   */
  Blockly.Scrollbar.prototype.isVisible = function() {
    return this.isVisible_;
  };
  
  /**
   * Set whether the scrollbar is visible.
   * Only applies to non-paired scrollbars.
   * @param {boolean} visible True if visible.
   */
  Blockly.Scrollbar.prototype.setVisible = function(visible) {
    if (visible == this.isVisible()) {
      return;
    }
    // Ideally this would also apply to scrollbar pairs, but that's a bigger
    // headache (due to interactions with the corner square).
    if (this.pair_) {
      throw 'Unable to toggle visibility of paired scrollbars.';
    }
  
    this.isVisible_ = visible;
  
    if (visible) {
      this.svgGroup_.setAttribute('display', 'block');
    } else {
      // Hide the scrollbar.
      this.workspace_.setMetrics({x: 0, y: 0});
      this.svgGroup_.setAttribute('display', 'none');
    }
  };
  
  /**
   * Scroll by one pageful.
   * Called when scrollbar background is clicked.
   * @param {!Event} e Mouse down event.
   * @private
   */
  Blockly.Scrollbar.prototype.onMouseDownBar_ = function(e) {
    this.workspace_.markFocused();
    Blockly.Touch.clearTouchIdentifier();  // This is really a click.
    this.cleanUp_();
    if (Blockly.isRightButton(e)) {
      // Right-click.
      // Scrollbars have no context menu.
      e.stopPropagation();
      return;
    }
    var mouseXY = Blockly.mouseToSvg(e, this.workspace_.getParentSvg(),
        this.workspace_.getInverseScreenCTM());
    var mouseLocation = this.horizontal_ ? mouseXY.x : mouseXY.y;
  
    var handleXY = Blockly.getSvgXY_(this.svgHandle_, this.workspace_);
    var handleStart = this.horizontal_ ? handleXY.x : handleXY.y;
    var handlePosition = this.handlePosition_;
  
    var pageLength = this.handleLength_ * 0.95;
    if (mouseLocation <= handleStart) {
      // Decrease the scrollbar's value by a page.
      handlePosition -= pageLength;
    } else if (mouseLocation >= handleStart + this.handleLength_) {
      // Increase the scrollbar's value by a page.
      handlePosition += pageLength;
    }
  
    this.setHandlePosition(this.constrainHandle_(handlePosition));
  
    this.onScroll_();
    e.stopPropagation();
    e.preventDefault();
  };
  
  /**
   * Start a dragging operation.
   * Called when scrollbar handle is clicked.
   * @param {!Event} e Mouse down event.
   * @private
   */
  Blockly.Scrollbar.prototype.onMouseDownHandle_ = function(e) {
    this.workspace_.markFocused();
    this.cleanUp_();
    if (Blockly.isRightButton(e)) {
      // Right-click.
      // Scrollbars have no context menu.
      e.stopPropagation();
      return;
    }
    // Look up the current translation and record it.
    this.startDragHandle = this.handlePosition_;
    // Record the current mouse position.
    this.startDragMouse = this.horizontal_ ? e.clientX : e.clientY;
    Blockly.Scrollbar.onMouseUpWrapper_ = Blockly.bindEventWithChecks_(document,
        'mouseup', this, this.onMouseUpHandle_);
    Blockly.Scrollbar.onMouseMoveWrapper_ = Blockly.bindEventWithChecks_(document,
        'mousemove', this, this.onMouseMoveHandle_);
    e.stopPropagation();
    e.preventDefault();
  };
  
  /**
   * Drag the scrollbar's handle.
   * @param {!Event} e Mouse up event.
   * @private
   */
  Blockly.Scrollbar.prototype.onMouseMoveHandle_ = function(e) {
    var currentMouse = this.horizontal_ ? e.clientX : e.clientY;
    var mouseDelta = currentMouse - this.startDragMouse;
    var handlePosition = this.startDragHandle + mouseDelta;
    // Position the bar.
    this.setHandlePosition(this.constrainHandle_(handlePosition));
    this.onScroll_();
  };
  
  /**
   * Release the scrollbar handle and reset state accordingly.
   * @private
   */
  Blockly.Scrollbar.prototype.onMouseUpHandle_ = function() {
    Blockly.Touch.clearTouchIdentifier();
    this.cleanUp_();
  };
  
  /**
   * Hide chaff and stop binding to mouseup and mousemove events.  Call this to
   * wrap up lose ends associated with the scrollbar.
   * @private
   */
  Blockly.Scrollbar.prototype.cleanUp_ = function() {
    Blockly.hideChaff(true);
    if (Blockly.Scrollbar.onMouseUpWrapper_) {
      Blockly.unbindEvent_(Blockly.Scrollbar.onMouseUpWrapper_);
      Blockly.Scrollbar.onMouseUpWrapper_ = null;
    }
    if (Blockly.Scrollbar.onMouseMoveWrapper_) {
      Blockly.unbindEvent_(Blockly.Scrollbar.onMouseMoveWrapper_);
      Blockly.Scrollbar.onMouseMoveWrapper_ = null;
    }
  };
  
  /**
   * Constrain the handle's position within the minimum (0) and maximum
   * (length of scrollbar) values allowed for the scrollbar.
   * @param {number} value Value that is potentially out of bounds.
   * @return {number} Constrained value.
   * @private
   */
  Blockly.Scrollbar.prototype.constrainHandle_ = function(value) {
    if (value <= 0 || isNaN(value) || this.scrollViewSize_ < this.handleLength_) {
      value = 0;
    } else {
      value = Math.min(value, this.scrollViewSize_ - this.handleLength_);
    }
    return value;
  };
  
  /**
   * Called when scrollbar is moved.
   * @private
   */
  Blockly.Scrollbar.prototype.onScroll_ = function() {
    var ratio = this.handlePosition_ / this.scrollViewSize_;
    if (isNaN(ratio)) {
      ratio = 0;
    }
    var xyRatio = {};
    if (this.horizontal_) {
      xyRatio.x = ratio;
    } else {
      xyRatio.y = ratio;
    }
    this.workspace_.setMetrics(xyRatio);
  };
  
  /**
   * Set the scrollbar slider's position.
   * @param {number} value The distance from the top/left end of the bar.
   */
  Blockly.Scrollbar.prototype.set = function(value) {
    this.setHandlePosition(this.constrainHandle_(value * this.ratio_));
    this.onScroll_();
  };
  
  /**
   * Insert a node after a reference node.
   * Contrast with node.insertBefore function.
   * @param {!Element} newNode New element to insert.
   * @param {!Element} refNode Existing element to precede new node.
   * @private
   */
  Blockly.Scrollbar.insertAfter_ = function(newNode, refNode) {
    var siblingNode = refNode.nextSibling;
    var parentNode = refNode.parentNode;
    if (!parentNode) {
      throw 'Reference node has no parent.';
    }
    if (siblingNode) {
      parentNode.insertBefore(newNode, siblingNode);
    } else {
      parentNode.appendChild(newNode);
    }
  };
  