[api-minor] Add basic support for PageLayout in the API and the viewer

Please see the specification, https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/PDF32000_2008.pdf#G6.2393749, and refer to the inline comments for additional details.

src/core/obj.js

@@ -376,6 +376,27 @@ class Catalog {
     return pageLabels;
   }
 
+  get pageLayout() {
+    const obj = this.catDict.get('PageLayout');
+    // Purposely use a non-standard default value, rather than 'SinglePage', to
+    // allow differentiating between `undefined` and /SinglePage since that does
+    // affect the Scroll mode (continuous/non-continuous) used in Adobe Reader.
+    let pageLayout = '';
+
+    if (isName(obj)) {
+      switch (obj.name) {
+        case 'SinglePage':
+        case 'OneColumn':
+        case 'TwoColumnLeft':
+        case 'TwoColumnRight':
+        case 'TwoPageLeft':
+        case 'TwoPageRight':
+          pageLayout = obj.name;
+      }
+    }
+    return shadow(this, 'pageLayout', pageLayout);
+  }
+
   get pageMode() {
     const obj = this.catDict.get('PageMode');
     let pageMode = 'UseNone'; // Default value.

src/core/worker.js

@@ -517,6 +517,10 @@ var WorkerMessageHandler = {
       }
     );
 
+    handler.on('GetPageLayout', function wphSetupGetPageLayout(data) {
+      return pdfManager.ensureCatalog('pageLayout');
+    });
+
     handler.on('GetPageMode', function wphSetupGetPageMode(data) {
       return pdfManager.ensureCatalog('pageMode');
     });

src/display/api.js

@@ -657,6 +657,14 @@ class PDFDocumentProxy {
     return this._transport.getPageLabels();
   }
 
+  /**
+   * @return {Promise} A promise that is resolved with a {string} containing
+   *   the page layout name.
+   */
+  getPageLayout() {
+    return this._transport.getPageLayout();
+  }
+
   /**
    * @return {Promise} A promise that is resolved with a {string} containing
    *   the page mode name.
@@ -2214,6 +2222,10 @@ class WorkerTransport {
     return this.messageHandler.sendWithPromise('GetPageLabels', null);
   }
 
+  getPageLayout() {
+    return this.messageHandler.sendWithPromise('GetPageLayout', null);
+  }
+
   getPageMode() {
     return this.messageHandler.sendWithPromise('GetPageMode', null);
   }

test/unit/api_spec.js

@@ -610,6 +610,24 @@ describe('api', function() {
       }).catch(done.fail);
     });
 
+    it('gets default page layout', function(done) {
+      var loadingTask = getDocument(buildGetDocumentParams('tracemonkey.pdf'));
+
+      loadingTask.promise.then(function(pdfDocument) {
+        return pdfDocument.getPageLayout();
+      }).then(function(mode) {
+        expect(mode).toEqual('');
+
+        loadingTask.destroy().then(done);
+      }).catch(done.fail);
+    });
+    it('gets non-default page layout', function(done) {
+      doc.getPageLayout().then(function(mode) {
+        expect(mode).toEqual('SinglePage');
+        done();
+      }).catch(done.fail);
+    });
+
     it('gets default page mode', function(done) {
       var loadingTask = getDocument(buildGetDocumentParams('tracemonkey.pdf'));
 

web/app.js

@@ -889,6 +889,8 @@ let PDFViewerApplication = {
 
     // Since the `setInitialView` call below depends on this being resolved,
     // fetch it early to avoid delaying initial rendering of the PDF document.
+    const pageLayoutPromise = pdfDocument.getPageLayout().catch(
+      function() { /* Avoid breaking initial rendering; ignoring errors. */ });
     const pageModePromise = pdfDocument.getPageMode().catch(
       function() { /* Avoid breaking initial rendering; ignoring errors. */ });
     const openActionDestPromise = pdfDocument.getOpenActionDestination().catch(
@@ -934,8 +936,8 @@ let PDFViewerApplication = {
       }).catch(() => { /* Unable to read from storage; ignoring errors. */ });
 
       Promise.all([
-        storePromise, pageModePromise, openActionDestPromise,
-      ]).then(async ([values = {}, pageMode, openActionDest]) => {
+        storePromise, pageLayoutPromise, pageModePromise, openActionDestPromise,
+      ]).then(async ([values = {}, pageLayout, pageMode, openActionDest]) => {
         const viewOnLoad = AppOptions.get('viewOnLoad');
 
         this._initializePdfHistory({
@@ -974,6 +976,9 @@ let PDFViewerApplication = {
         if (pageMode && sidebarView === SidebarView.UNKNOWN) {
           sidebarView = apiPageModeToSidebarView(pageMode);
         }
+        if (pageLayout && spreadMode === SpreadMode.UNKNOWN) {
+          spreadMode = apiPageLayoutToSpreadMode(pageLayout);
+        }
 
         this.setInitialView(hash, {
           rotation, sidebarView, scrollMode, spreadMode,
@@ -2434,6 +2439,29 @@ function webViewerKeyDown(evt) {
   }
 }
 
+/**
+ * Converts API PageLayout values to the format used by `PDFViewer`.
+ * NOTE: This is supported to the extent that the viewer implements the
+ *       necessary Scroll/Spread modes (since SinglePage, TwoPageLeft,
+ *       and TwoPageRight all suggests using non-continuous scrolling).
+ * @param {string} mode - The API PageLayout value.
+ * @returns {number} A value from {SpreadMode}.
+ */
+function apiPageLayoutToSpreadMode(layout) {
+  switch (layout) {
+    case 'SinglePage':
+    case 'OneColumn':
+      return SpreadMode.NONE;
+    case 'TwoColumnLeft':
+    case 'TwoPageLeft':
+      return SpreadMode.ODD;
+    case 'TwoColumnRight':
+    case 'TwoPageRight':
+      return SpreadMode.EVEN;
+  }
+  return SpreadMode.NONE; // Default value.
+}
+
 /**
  * Converts API PageMode values to the format used by `PDFSidebar`.
  * NOTE: There's also a "FullScreen" parameter which is not possible to support,