Let getVisibleElements return a Set containing the visible element ids

Note how in `PDFPageViewBuffer.resize` we're manually iterating through the visible pages in order to build a Set of the visible page `id`s. By instead moving the building of this Set into the `getVisibleElements` helper function, as part of the existing parsing, this code becomes *ever so slightly* more efficient.

Furthermore, more direct access to the visible page `id`s also come in handy in other parts of the viewer as well.
In the `BaseViewer.isPageVisible` method we no longer need to loop through the visible pages, but can instead directly check if the pageNumber is visible.
In the `PDFRenderingQueue.getHighestPriority` method, when checking for "holes" in the page layout, we can also avoid some unnecessary look-ups this way.

test/unit/ui_utils_spec.js

@@ -497,7 +497,8 @@ describe("ui_utils", function () {
     // This is a reimplementation of getVisibleElements without the
     // optimizations.
     function slowGetVisibleElements(scroll, pages) {
-      const views = [];
+      const views = [],
+        ids = new Set();
       const { scrollLeft, scrollTop } = scroll;
       const scrollRight = scrollLeft + scroll.clientWidth;
       const scrollBottom = scrollTop + scroll.clientHeight;
@@ -535,9 +536,10 @@ describe("ui_utils", function () {
             percent,
             widthPercent: (fractionWidth * 100) | 0,
           });
+          ids.add(view.id);
         }
       }
-      return { first: views[0], last: views[views.length - 1], views };
+      return { first: views[0], last: views[views.length - 1], views, ids };
     }
 
     // This function takes a fixed layout of pages and compares the system under
@@ -699,6 +701,7 @@ describe("ui_utils", function () {
         first: undefined,
         last: undefined,
         views: [],
+        ids: new Set(),
       });
     });
 
@@ -715,6 +718,7 @@ describe("ui_utils", function () {
         first: undefined,
         last: undefined,
         views: [],
+        ids: new Set(),
       });
     });
 

web/base_viewer.js

@@ -104,22 +104,19 @@ function PDFPageViewBuffer(size) {
       data.shift().destroy();
     }
   };
+
   /**
-   * After calling resize, the size of the buffer will be newSize. The optional
+   * After calling resize, the size of the buffer will be `newSize`.
-   * parameter pagesToKeep is, if present, an array of pages to push to the back
+   * The optional parameter `idsToKeep` is, if present, a Set of page-ids to
-   * of the buffer, delaying their destruction. The size of pagesToKeep has no
+   * push to the back of the buffer, delaying their destruction. The size of
-   * impact on the final size of the buffer; if pagesToKeep has length larger
+   * `idsToKeep` has no impact on the final size of the buffer; if `idsToKeep`
-   * than newSize, some of those pages will be destroyed anyway.
+   * is larger than `newSize`, some of those pages will be destroyed anyway.
    */
-  this.resize = function (newSize, pagesToKeep) {
+  this.resize = function (newSize, idsToKeep = null) {
     size = newSize;
-    if (pagesToKeep) {
+    if (idsToKeep) {
-      const pageIdsToKeep = new Set();
-      for (let i = 0, iMax = pagesToKeep.length; i < iMax; ++i) {
-        pageIdsToKeep.add(pagesToKeep[i].id);
-      }
       moveToEndOfArray(data, function (page) {
-        return pageIdsToKeep.has(page.id);
+        return idsToKeep.has(page.id);
       });
     }
     while (data.length > size) {
@@ -1145,7 +1142,7 @@ class BaseViewer {
       return;
     }
     const newCacheSize = Math.max(DEFAULT_CACHE_SIZE, 2 * numVisiblePages + 1);
-    this._buffer.resize(newCacheSize, visiblePages);
+    this._buffer.resize(newCacheSize, visible.ids);
 
     this.renderingQueue.renderHighestPriority(visible);
 
@@ -1231,7 +1228,9 @@ class BaseViewer {
       y: element.offsetTop + element.clientTop,
       view: pageView,
     };
-    return { first: view, last: view, views: [view] };
+    const ids = new Set([pageView.id]);
+
+    return { first: view, last: view, views: [view], ids };
   }
 
   _getVisiblePages() {
@@ -1273,16 +1272,14 @@ class BaseViewer {
       console.error(`isPageVisible: "${pageNumber}" is not a valid page.`);
       return false;
     }
-    return this._getVisiblePages().views.some(function (view) {
+    return this._getVisiblePages().ids.has(pageNumber);
-      return view.id === pageNumber;
-    });
   }
 
   /**
    * @param {number} pageNumber
    */
   isPageCached(pageNumber) {
-    if (!this.pdfDocument || !this._buffer) {
+    if (!this.pdfDocument) {
       return false;
     }
     if (
@@ -1296,9 +1293,6 @@ class BaseViewer {
       return false;
     }
     const pageView = this._pages[pageNumber - 1];
-    if (!pageView) {
-      return false;
-    }
     return this._buffer.has(pageView);
   }
 

web/pdf_rendering_queue.js

@@ -133,9 +133,13 @@ class PDFRenderingQueue {
     // All the visible views have rendered; try to handle any "holes" in the
     // page layout (can happen e.g. with spreadModes at higher zoom levels).
     if (lastId - firstId + 1 > numVisible) {
+      const visibleIds = visible.ids;
       for (let i = 1, ii = lastId - firstId; i < ii; i++) {
-        const holeId = scrolledDown ? firstId + i : lastId - i,
+        const holeId = scrolledDown ? firstId + i : lastId - i;
-          holeView = views[holeId - 1];
+        if (visibleIds.has(holeId)) {
+          continue;
+        }
+        const holeView = views[holeId - 1];
         if (!this.isViewFinished(holeView)) {
           return holeView;
         }

web/ui_utils.js

@@ -473,6 +473,7 @@ function getVisibleElements({
   }
 
   const visible = [],
+    ids = new Set(),
     numViews = views.length;
   let firstVisibleElementInd = binarySearchFirstItem(
     views,
@@ -558,6 +559,7 @@ function getVisibleElements({
       percent,
       widthPercent: (fractionWidth * 100) | 0,
     });
+    ids.add(view.id);
   }
 
   const first = visible[0],
@@ -572,7 +574,7 @@ function getVisibleElements({
       return a.id - b.id; // ensure stability
     });
   }
-  return { first, last, views: visible };
+  return { first, last, views: visible, ids };
 }
 
 /**