Implement viewporting for the out of process PDF plugin.

chrome/browser/resources/pdf/viewport.js

+// Copyright 2013 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.
+
+/**
+ * Predefined zoom factors to be used when zooming in/out. These are in
+ * ascending order.
+ */
+var ZOOM_FACTORS = [0.25, 0.333, 0.5, 0.666, 0.75, 0.9, 1,
+                    1.1, 1.25, 1.5, 1.75, 2, 2.5, 3, 4, 5];
+
+/**
+ * Returns the area of the intersection of two rectangles.
+ * @param {Object} rect1 the first rect
+ * @param {Object} rect2 the second rect
+ * @return {number} the area of the intersection of the rects
+ */
+function getIntersectionArea(rect1, rect2) {
+  var xOverlap = Math.max(0,
+      Math.min(rect1.x + rect1.width, rect2.x + rect2.width) -
+      Math.max(rect1.x, rect2.x));
+  var yOverlap = Math.max(0,
+      Math.min(rect1.y + rect1.height, rect2.y + rect2.height) -
+      Math.max(rect1.y, rect2.y));
+  return xOverlap * yOverlap;
+}
+
+/**
+ * @return {number} width of a scrollbar in pixels
+ */
+function getScrollbarWidth() {
+  var parentDiv = document.createElement('div');
+  parentDiv.style.visibility = 'hidden';
+  var parentDivWidth = 500;
+  parentDiv.style.width = parentDivWidth + 'px';
+  document.body.appendChild(parentDiv);
+  parentDiv.style.overflow = 'scroll';
+  var childDiv = document.createElement('div');
+  childDiv.style.width = '100%';
+  parentDiv.appendChild(childDiv);
+  var childDivWidth = childDiv.offsetWidth;
+  parentDiv.parentNode.removeChild(parentDiv);
+  return parentDivWidth - childDivWidth;
+}
+
+/**
+ * Create a new viewport.
+ * @param {Window} window the window
+ * @param {Object} sizer is the element which represents the size of the
+ *     document in the viewport
+ * @param {Function} fitToPageEnabledFunction returns true if fit-to-page is
+ *     enabled
+ * @param {Function} viewportChangedCallback is run when the viewport changes
+ */
+function Viewport(window,
+                  sizer,
+                  fitToPageEnabledFunction,
+                  viewportChangedCallback) {
+  this.window_ = window;
+  this.sizer_ = sizer;
+  this.fitToPageEnabledFunction_ = fitToPageEnabledFunction;
+  this.viewportChangedCallback_ = viewportChangedCallback;
+  this.zoom_ = 1;
+  this.documentDimensions_ = {};
+  this.pageDimensions_ = [];
+  this.scrollbarWidth_ = getScrollbarWidth();
+
+  window.addEventListener('scroll', this.updateViewport_.bind(this));
+}
+
+Viewport.prototype = {
+  /**
+   * @private
+   * Returns true if the document needs scrollbars at the given zoom level.
+   * @param {number} zoom compute whether scrollbars are needed at this zoom
+   * @return {Object} with 'x' and 'y' keys which map to bool values
+   *     indicating if the horizontal and vertical scrollbars are needed
+   *     respectively.
+   */
+  documentNeedsScrollbars_: function(zoom) {
+    return {
+      x: this.documentDimensions_.width * zoom > this.window_.innerWidth,
+      y: this.documentDimensions_.height * zoom > this.window_.innerHeight
+    };
+  },
+
+  /**
+   * Returns true if the document needs scrollbars at the current zoom level.
+   * @return {Object} with 'x' and 'y' keys which map to bool values
+   *     indicating if the horizontal and vertical scrollbars are needed
+   *     respectively.
+   */
+  documentHasScrollbars: function() {
+    return this.documentNeedsScrollbars_(this.zoom_);
+  },
+
+  /**
+   * @private
+   * Helper function called when the zoomed document size changes.
+   */
+  contentSizeChanged_: function() {
+    this.sizer_.style.width =
+        this.documentDimensions_.width * this.zoom_ + 'px';
+    this.sizer_.style.height =
+        this.documentDimensions_.height * this.zoom_ + 'px';
+  },
+
+  /**
+   * Sets the zoom of the viewport.
+   * @param {number} newZoom the zoom level to zoom to
+   */
+  setZoom: function(newZoom) {
+    var oldZoom = this.zoom_;
+    this.zoom_ = newZoom;
+    // Record the scroll position (relative to the middle of the window).
+    var currentScrollPos = [
+      (this.window_.scrollX + this.window_.innerWidth / 2) / oldZoom,
+      (this.window_.scrollY + this.window_.innerHeight / 2) / oldZoom
+    ];
+    this.contentSizeChanged_();
+    // Scroll to the scaled scroll position.
+    this.window_.scrollTo(
+        currentScrollPos[0] * newZoom - this.window_.innerWidth / 2,
+        currentScrollPos[1] * newZoom - this.window_.innerHeight / 2);
+  },
+
+  /**
+   * @private
+   * Called when the viewport should be updated.
+   */
+  updateViewport_: function() {
+    // Shift the toolbar so that it doesn't move when the scrollbars display
+    var needsScrollbars = this.documentHasScrollbars();
+    this.viewportChangedCallback_(this.zoom_,
+                                  this.window_.pageXOffset,
+                                  this.window_.pageYOffset,
+                                  this.scrollbarWidth_,
+                                  needsScrollbars);
+  },
+
+  /**
+   * @private
+   * Returns a rect representing the current viewport.
+   * @return {Object} a rect representing the current viewport.
+   */
+  getCurrentViewportRect_: function() {
+    return {
+      x: this.window_.pageXOffset / this.zoom_,
+      y: this.window_.pageYOffset / this.zoom_,
+      width: this.window_.innerWidth / this.zoom_,
+      height: this.window_.innerHeight / this.zoom_,
+    };
+  },
+
+  /**
+   * Returns the page with the most pixels in the current viewport.
+   * @return {int} the index of the most visible page.
+   */
+  getMostVisiblePage: function() {
+    // TODO(raymes): Do a binary search here.
+    var mostVisiblePage = {'number': 0, 'area': 0};
+    for (var i = 0; i < this.pageDimensions_.length; i++) {
+      var area = getIntersectionArea(this.pageDimensions_[i],
+                                     this.getCurrentViewportRect_());
+      if (area > mostVisiblePage.area) {
+        mostVisiblePage.area = area;
+        mostVisiblePage.number = i;
+      }
+    }
+    return mostVisiblePage.number;
+  },
+
+  /**
+   * @private
+   * Compute the zoom level for fit-to-page or fit-to-width. |pageDimensions| is
+   * the dimensions for a given page and if |widthOnly| is true, it indicates
+   * that fit-to-page zoom should be computed rather than fit-to-page.
+   * @param {Object} pageDimensions the dimensions of a given page
+   * @param {boolean} widthOnly a bool indicating whether fit-to-page or
+   *     fit-to-width should be computed.
+   * @return {number} the zoom to use
+   */
+  computeFittingZoom_: function(pageDimensions, widthOnly) {
+    // First compute the zoom without scrollbars.
+    var zoomWidth = this.window_.innerWidth / pageDimensions.width;
+    var zoom;
+    if (widthOnly) {
+      zoom = zoomWidth;
+    } else {
+      var zoomHeight = this.window_.innerHeight / pageDimensions.height;
+      zoom = Math.min(zoomWidth, zoomHeight);
+    }
+    // Check if there needs to be any scrollbars.
+    var needsScrollbars = this.documentNeedsScrollbars_(zoom);
+
+    // If the document fits, just return the zoom.
+    if (!needsScrollbars.x && !needsScrollbars.y)
+      return zoom;
+
+    var zoomedDimensions = {
+      width: this.documentDimensions_.width * zoom,
+      height: this.documentDimensions_.height * zoom
+    };
+
+    // Check if adding a scrollbar will result in needing the other scrollbar.
+    var scrollbarWidth = this.scrollbarWidth_;
+    if (needsScrollbars.x &&
+        zoomedDimensions.height > this.window_.innerHeight - scrollbarWidth) {
+      needsScrollbars.y = true;
+    }
+    if (needsScrollbars.y &&
+        zoomedDimensions.width > this.window_.innerWidth - scrollbarWidth) {
+      needsScrollbars.x = true;
+    }
+
+    // Compute available window space.
+    var windowWithScrollbars = {
+      width: this.window_.innerWidth,
+      height: this.window_.innerHeight
+    };
+    if (needsScrollbars.x)
+      windowWithScrollbars.height -= scrollbarWidth;
+    if (needsScrollbars.y)
+      windowWithScrollbars.width -= scrollbarWidth;
+
+    // Recompute the zoom.
+    zoomWidth = windowWithScrollbars.width / pageDimensions.width;
+    if (widthOnly) {
+      zoom = zoomWidth;
+    } else {
+      var zoomHeight = windowWithScrollbars.height / pageDimensions.height;
+      zoom = Math.min(zoomWidth, zoomHeight);
+    }
+    return zoom;
+  },
+
+  /**
+   * Zoom the viewport so that the page-width consumes the entire viewport.
+   */
+  fitToWidth: function() {
+    var page = this.getMostVisiblePage();
+    this.setZoom(this.computeFittingZoom_(this.pageDimensions_[page], true));
+    this.window_.scrollTo(this.pageDimensions_[page].x * this.zoom_,
+                          this.window_.scrollY);
+    this.updateViewport_();
+  },
+
+  /**
+   * Zoom the viewport so that a page consumes the entire viewport. Also scrolls
+   * to the top of the most visible page.
+   */
+  fitToPage: function() {
+    var page = this.getMostVisiblePage();
+    this.setZoom(this.computeFittingZoom_(this.pageDimensions_[page], false));
+    this.window_.scrollTo(this.pageDimensions_[page].x * this.zoom_,
+                          this.pageDimensions_[page].y * this.zoom_);
+    this.updateViewport_();
+  },
+
+  /**
+   * Zoom out to the next predefined zoom level.
+   */
+  zoomOut: function() {
+    var nextZoom = ZOOM_FACTORS[0];
+    for (var i = 0; i < ZOOM_FACTORS.length; i++) {
+      if (ZOOM_FACTORS[i] < this.zoom_)
+        nextZoom = ZOOM_FACTORS[i];
+    }
+    this.setZoom(nextZoom);
+    this.updateViewport_();
+  },
+
+  /**
+   * Zoom in to the next predefined zoom level.
+   */
+  zoomIn: function() {
+    var nextZoom = ZOOM_FACTORS[ZOOM_FACTORS.length - 1];
+    for (var i = ZOOM_FACTORS.length - 1; i >= 0; i--) {
+      if (ZOOM_FACTORS[i] > this.zoom_)
+        nextZoom = ZOOM_FACTORS[i];
+    }
+    this.setZoom(nextZoom);
+    this.updateViewport_();
+  },
+
+  /**
+   * Go to the given page index.
+   * @param {number} page the index of the page to go to
+   */
+  goToPage: function(page) {
+    if (page < 0)
+      page = 0;
+    var dimensions = this.pageDimensions_[page];
+    this.window_.scrollTo(dimensions.x * this.zoom_, dimensions.y * this.zoom_);
+  },
+
+  /**
+   * Set the dimensions of the document.
+   * @param {Object} documentDimensions the dimensions of the document
+   */
+  setDocumentDimensions: function(documentDimensions) {
+    this.documentDimensions_ = documentDimensions;
+    this.pageDimensions_ = this.documentDimensions_.pageDimensions;
+    this.contentSizeChanged_();
+    this.updateViewport_();
+  }
+};