Add spread modes to web viewer

This builds on the scrolling mode work to add three buttons for joining
page spreads together: one for the default view, with no page spreads,
and two for spreads starting on odd-numbered or even-numbered pages.

l10n/en-US/viewer.properties

@@ -72,6 +72,13 @@ scroll_horizontal_label=Horizontal Scrolling
 scroll_wrapped.title=Use Wrapped Scrolling
 scroll_wrapped_label=Wrapped Scrolling
 
+spread_none.title=Do not join page spreads
+spread_none_label=No Spreads
+spread_odd.title=Join page spreads starting with odd-numbered pages
+spread_odd_label=Odd Spreads
+spread_even.title=Join page spreads starting with even-numbered pages
+spread_even_label=Even Spreads
+
 # Document properties dialog box
 document_properties.title=Document Properties…
 document_properties_label=Document Properties…

web/app.js

@@ -1386,6 +1386,7 @@ let PDFViewerApplication = {
     eventBus.on('rotatecw', webViewerRotateCw);
     eventBus.on('rotateccw', webViewerRotateCcw);
     eventBus.on('switchscrollmode', webViewerSwitchScrollMode);
+    eventBus.on('switchspreadmode', webViewerSwitchSpreadMode);
     eventBus.on('documentproperties', webViewerDocumentProperties);
     eventBus.on('find', webViewerFind);
     eventBus.on('findfromurlhash', webViewerFindFromUrlHash);
@@ -1453,6 +1454,7 @@ let PDFViewerApplication = {
     eventBus.off('rotatecw', webViewerRotateCw);
     eventBus.off('rotateccw', webViewerRotateCcw);
     eventBus.off('switchscrollmode', webViewerSwitchScrollMode);
+    eventBus.off('switchspreadmode', webViewerSwitchSpreadMode);
     eventBus.off('documentproperties', webViewerDocumentProperties);
     eventBus.off('find', webViewerFind);
     eventBus.off('findfromurlhash', webViewerFindFromUrlHash);
@@ -1965,6 +1967,9 @@ function webViewerRotateCcw() {
 function webViewerSwitchScrollMode(evt) {
   PDFViewerApplication.pdfViewer.setScrollMode(evt.mode);
 }
+function webViewerSwitchSpreadMode(evt) {
+  PDFViewerApplication.pdfViewer.setSpreadMode(evt.mode);
+}
 function webViewerDocumentProperties() {
   PDFViewerApplication.pdfDocumentProperties.open();
 }

web/base_viewer.js

@@ -35,6 +35,12 @@ const ScrollMode = {
   WRAPPED: 2,
 };
 
+const SpreadMode = {
+  NONE: 0, // The default value.
+  ODD: 1,
+  EVEN: 2,
+};
+
 /**
  * @typedef {Object} PDFViewerOptions
  * @property {HTMLDivElement} container - The container for the viewer element.
@@ -71,6 +77,10 @@ const ScrollMode = {
  *   document pages should be laid out within the scrolling container. The
  *   constants from {ScrollMode} should be used. The default value is
  *   `ScrollMode.VERTICAL`.
+ * @property {number} spreadMode - (optional) If not `SpreadMode.NONE`, groups
+ *   pages into spreads, starting with odd- or even-numbered pages. The
+ *   constants from {SpreadMode} should be used. The default value is
+ *   `SpreadMode.NONE`.
  */
 
 function PDFPageViewBuffer(size) {
@@ -153,6 +163,7 @@ class BaseViewer {
     this.maxCanvasPixels = options.maxCanvasPixels;
     this.l10n = options.l10n || NullL10n;
     this.scrollMode = options.scrollMode || ScrollMode.VERTICAL;
+    this.spreadMode = options.spreadMode || SpreadMode.NONE;
 
     this.defaultRenderingQueue = !options.renderingQueue;
     if (this.defaultRenderingQueue) {
@@ -428,6 +439,9 @@ class BaseViewer {
         bindOnAfterAndBeforeDraw(pageView);
         this._pages.push(pageView);
       }
+      if (this.spreadMode !== SpreadMode.NONE) {
+        this._regroupSpreads();
+      }
 
       // Fetch all the pages since the viewport is needed before printing
       // starts to create the correct size canvas. Wait until one page is
@@ -1020,9 +1034,20 @@ class BaseViewer {
     classList.toggle('scrollHorizontal', mode === ScrollMode.HORIZONTAL);
     classList.toggle('scrollWrapped', mode === ScrollMode.WRAPPED);
   }
+
+  setSpreadMode(mode) {
+    if (mode !== this.spreadMode) {
+      this.spreadMode = mode;
+      this.eventBus.dispatch('spreadmodechanged', { mode, });
+      this._regroupSpreads();
+    }
+  }
+
+  _regroupSpreads() {}
 }
 
 export {
   BaseViewer,
   ScrollMode,
+  SpreadMode,
 };

web/pdf_viewer.css

@@ -46,29 +46,40 @@
   border: none;
 }
 
-.pdfViewer.scrollHorizontal, .pdfViewer.scrollWrapped {
+.pdfViewer.scrollHorizontal, .pdfViewer.scrollWrapped, .spread {
   margin-left: 3.5px;
   margin-right: 3.5px;
   text-align: center;
 }
 
-.pdfViewer.scrollHorizontal {
+.pdfViewer.scrollHorizontal, .spread {
   white-space: nowrap;
 }
 
-.pdfViewer.removePageBorders {
+.pdfViewer.removePageBorders,
+.pdfViewer.scrollHorizontal .spread,
+.pdfViewer.scrollWrapped .spread {
   margin-left: 0;
   margin-right: 0;
 }
 
+.spread .page,
 .pdfViewer.scrollHorizontal .page,
-.pdfViewer.scrollWrapped .page {
+.pdfViewer.scrollWrapped .page,
+.pdfViewer.scrollHorizontal .spread,
+.pdfViewer.scrollWrapped .spread {
   display: inline-block;
-  margin-left: -3.5px;
-  margin-right: -3.5px;
   vertical-align: middle;
 }
 
+.spread .page,
+.pdfViewer.scrollHorizontal .page,
+.pdfViewer.scrollWrapped .page {
+  margin-left: -3.5px;
+  margin-right: -3.5px;
+}
+
+.pdfViewer.removePageBorders .spread .page,
 .pdfViewer.removePageBorders.scrollHorizontal .page,
 .pdfViewer.removePageBorders.scrollWrapped .page {
   margin-left: 5px;
@@ -99,7 +110,8 @@
   margin-right: 0;
 }
 
-.pdfPresentationMode .pdfViewer .page {
+.pdfPresentationMode .pdfViewer .page,
+.pdfPresentationMode .pdfViewer .spread {
   display: block;
 }
 

web/pdf_viewer.js

@@ -13,7 +13,7 @@
  * limitations under the License.
  */
 
-import { BaseViewer, ScrollMode } from './base_viewer';
+import { BaseViewer, ScrollMode, SpreadMode } from './base_viewer';
 import { getVisibleElements, scrollIntoView } from './ui_utils';
 import { shadow } from 'pdfjs-lib';
 
@@ -23,9 +23,15 @@ class PDFViewer extends BaseViewer {
   }
 
   _scrollIntoView({ pageDiv, pageSpot = null, }) {
-    if (!pageSpot && this.scrollMode === ScrollMode.HORIZONTAL) {
+    if (!pageSpot) {
+      const left = pageDiv.offsetLeft + pageDiv.clientLeft;
+      const right = left + pageDiv.clientWidth;
+      const { scrollLeft, clientWidth, } = this.container;
+      if (this.scrollMode === ScrollMode.HORIZONTAL ||
+          left < scrollLeft || right > scrollLeft + clientWidth) {
         pageSpot = { left: 0, top: 0, };
       }
+    }
     scrollIntoView(pageDiv, pageSpot);
   }
 
@@ -80,6 +86,34 @@ class PDFViewer extends BaseViewer {
       location: this._location,
     });
   }
+
+  _regroupSpreads() {
+    const container = this._setDocumentViewerElement, pages = this._pages;
+    while (container.firstChild) {
+      container.firstChild.remove();
+    }
+    if (this.spreadMode === SpreadMode.NONE) {
+      for (let i = 0, iMax = pages.length; i < iMax; ++i) {
+        container.appendChild(pages[i].div);
+      }
+    } else {
+      const parity = this.spreadMode - 1;
+      let spread = null;
+      for (let i = 0, iMax = pages.length; i < iMax; ++i) {
+        if (spread === null) {
+          spread = document.createElement('div');
+          spread.className = 'spread';
+          container.appendChild(spread);
+        } else if (i % 2 === parity) {
+          spread = spread.cloneNode(false);
+          container.appendChild(spread);
+        }
+        spread.appendChild(pages[i].div);
+      }
+    }
+    this.scrollPageIntoView({ pageNumber: this._currentPageNumber, });
+    this.update();
+  }
 }
 
 export {

web/secondary_toolbar.js

@@ -13,9 +13,9 @@
  * limitations under the License.
  */
 
+import { ScrollMode, SpreadMode } from './base_viewer';
 import { CursorTool } from './pdf_cursor_tools';
 import { SCROLLBAR_PADDING } from './ui_utils';
-import { ScrollMode } from './base_viewer';
 
 /**
  * @typedef {Object} SecondaryToolbarOptions
@@ -83,6 +83,12 @@ class SecondaryToolbar {
         eventDetails: { mode: ScrollMode.HORIZONTAL, }, close: true, },
       { element: options.scrollWrappedButton, eventName: 'switchscrollmode',
         eventDetails: { mode: ScrollMode.WRAPPED, }, close: true, },
+      { element: options.spreadNoneButton, eventName: 'switchspreadmode',
+        eventDetails: { mode: SpreadMode.NONE, }, close: true, },
+      { element: options.spreadOddButton, eventName: 'switchspreadmode',
+        eventDetails: { mode: SpreadMode.ODD, }, close: true, },
+      { element: options.spreadEvenButton, eventName: 'switchspreadmode',
+        eventDetails: { mode: SpreadMode.EVEN, }, close: true, },
       { element: options.documentPropertiesButton,
         eventName: 'documentproperties', close: true, },
     ];
@@ -102,10 +108,12 @@ class SecondaryToolbar {
 
     this.reset();
 
-    // Bind the event listeners for click, cursor tool, and scroll mode actions.
+    // Bind the event listeners for click, cursor tool, and scroll/spread mode
+    // actions.
     this._bindClickListeners();
     this._bindCursorToolsListener(options);
     this._bindScrollModeListener(options);
+    this._bindSpreadModeListener(options);
 
     // Bind the event listener for adjusting the 'max-height' of the toolbar.
     this.eventBus.on('resize', this._setMaxHeight.bind(this));
@@ -191,6 +199,17 @@ class SecondaryToolbar {
     });
   }
 
+  _bindSpreadModeListener(buttons) {
+    this.eventBus.on('spreadmodechanged', function(evt) {
+      buttons.spreadNoneButton.classList.toggle('toggled',
+        evt.mode === SpreadMode.NONE);
+      buttons.spreadOddButton.classList.toggle('toggled',
+        evt.mode === SpreadMode.ODD);
+      buttons.spreadEvenButton.classList.toggle('toggled',
+        evt.mode === SpreadMode.EVEN);
+    });
+  }
+
   open() {
     if (this.opened) {
       return;

web/ui_utils.js

@@ -316,9 +316,10 @@ function getPageSizeInches({ view, userUnit, rotate, }) {
  */
 function backtrackBeforeAllVisibleElements(index, views, top) {
   // binarySearchFirstItem's assumption is that the input is ordered, with only
-  // one index where the conditions flips from false to true:
-  // [false ..., true...]. With wrapped scrolling, it is possible to have
-  // [false ..., true, false, true ...].
+  // one index where the conditions flips from false to true: [false ...,
+  // true...]. With vertical scrolling and spreads, it is possible to have
+  // [false ..., true, false, true ...]. With wrapped scrolling we can have a
+  // similar sequence, with many more mixed true and false in the middle.
   //
   // So there is no guarantee that the binary search yields the index of the
   // first visible element. It could have been any of the other visible elements
@@ -451,10 +452,11 @@ function getVisibleElements(scrollEl, views, sortByVisibility = false,
                                               isElementBottomAfterViewTop);
 
   if (views.length > 0 && !horizontal) {
-    // In wrapped scrolling, with some page sizes, isElementBottomAfterViewTop
-    // doesn't satisfy the binary search condition: there can be pages with
-    // bottoms above the view top between pages with bottoms below. This
-    // function detects and corrects that error; see it for more comments.
+    // In wrapped scrolling (or vertical scrolling with spreads), with some page
+    // sizes, isElementBottomAfterViewTop doesn't satisfy the binary search
+    // condition: there can be pages with bottoms above the view top between
+    // pages with bottoms below. This function detects and corrects that error;
+    // see it for more comments.
     firstVisibleElementInd =
       backtrackBeforeAllVisibleElements(firstVisibleElementInd, views, top);
   }
@@ -462,11 +464,11 @@ function getVisibleElements(scrollEl, views, sortByVisibility = false,
   // lastEdge acts as a cutoff for us to stop looping, because we know all
   // subsequent pages will be hidden.
   //
-  // When using wrapped scrolling, we can't simply stop the first time we reach
-  // a page below the bottom of the view; the tops of subsequent pages on the
-  // same row could still be visible. In horizontal scrolling, we don't have
-  // that issue, so we can stop as soon as we pass `right`, without needing the
-  // code below that handles the -1 case.
+  // When using wrapped scrolling or vertical scrolling with spreads, we can't
+  // simply stop the first time we reach a page below the bottom of the view;
+  // the tops of subsequent pages on the same row could still be visible. In
+  // horizontal scrolling, we don't have that issue, so we can stop as soon as
+  // we pass `right`, without needing the code below that handles the -1 case.
   let lastEdge = horizontal ? right : -1;
 
   for (let i = firstVisibleElementInd, ii = views.length; i < ii; i++) {

web/viewer.css

@@ -978,6 +978,18 @@ html[dir="rtl"] .secondaryToolbarButton > span {
   content: url(images/secondaryToolbarButton-scrollWrapped.png);
 }
 
+.secondaryToolbarButton.spreadNone::before {
+  content: url(images/secondaryToolbarButton-spreadNone.png);
+}
+
+.secondaryToolbarButton.spreadOdd::before {
+  content: url(images/secondaryToolbarButton-spreadOdd.png);
+}
+
+.secondaryToolbarButton.spreadEven::before {
+  content: url(images/secondaryToolbarButton-spreadEven.png);
+}
+
 .secondaryToolbarButton.documentProperties::before {
   content: url(images/secondaryToolbarButton-documentProperties.png);
 }
@@ -1713,6 +1725,18 @@ html[dir='rtl'] #documentPropertiesOverlay .row > * {
     content: url(images/secondaryToolbarButton-scrollWrapped@2x.png);
   }
 
+  .secondaryToolbarButton.spreadNone::before {
+    content: url(images/secondaryToolbarButton-spreadNone@2x.png);
+  }
+
+  .secondaryToolbarButton.spreadOdd::before {
+    content: url(images/secondaryToolbarButton-spreadOdd@2x.png);
+  }
+
+  .secondaryToolbarButton.spreadEven::before {
+    content: url(images/secondaryToolbarButton-spreadEven@2x.png);
+  }
+
   .secondaryToolbarButton.documentProperties::before {
     content: url(images/secondaryToolbarButton-documentProperties@2x.png);
   }

web/viewer.html

@@ -180,7 +180,19 @@ See https://github.com/adobe-type-tools/cmap-resources
 
             <div class="horizontalToolbarSeparator"></div>
 
-            <button id="documentProperties" class="secondaryToolbarButton documentProperties" title="Document Properties…" tabindex="65" data-l10n-id="document_properties">
+            <button id="spreadNone" class="secondaryToolbarButton spreadNone toggled" title="Do not join page spreads" tabindex="65" data-l10n-id="spread_none">
+              <span data-l10n-id="spread_none_label">No Spreads</span>
+            </button>
+            <button id="spreadOdd" class="secondaryToolbarButton spreadOdd" title="Join page spreads starting with odd-numbered pages" tabindex="66" data-l10n-id="spread_odd">
+              <span data-l10n-id="spread_odd_label">Odd Spreads</span>
+            </button>
+            <button id="spreadEven" class="secondaryToolbarButton spreadEven" title="Join page spreads starting with even-numbered pages" tabindex="67" data-l10n-id="spread_even">
+              <span data-l10n-id="spread_even_label">Even Spreads</span>
+            </button>
+
+            <div class="horizontalToolbarSeparator"></div>
+
+            <button id="documentProperties" class="secondaryToolbarButton documentProperties" title="Document Properties…" tabindex="68" data-l10n-id="document_properties">
               <span data-l10n-id="document_properties_label">Document Properties…</span>
             </button>
           </div>

web/viewer.js

@@ -99,6 +99,9 @@ function getViewerConfiguration() {
       scrollVerticalButton: document.getElementById('scrollVertical'),
       scrollHorizontalButton: document.getElementById('scrollHorizontal'),
       scrollWrappedButton: document.getElementById('scrollWrapped'),
+      spreadNoneButton: document.getElementById('spreadNone'),
+      spreadOddButton: document.getElementById('spreadOdd'),
+      spreadEvenButton: document.getElementById('spreadEven'),
       documentPropertiesButton: document.getElementById('documentProperties'),
     },
     fullscreen: {