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web/pdf_rendering_queue.js

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+/* Copyright 2012 Mozilla Foundation
+ *
+ * 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.
+ */
+
+/** @typedef {import("./interfaces").IRenderableView} IRenderableView */
+/** @typedef {import("./pdf_viewer").PDFViewer} PDFViewer */
+// eslint-disable-next-line max-len
+/** @typedef {import("./pdf_thumbnail_viewer").PDFThumbnailViewer} PDFThumbnailViewer */
+
+import { RenderingCancelledException } from "pdfjs-lib";
+import { RenderingStates } from "./ui_utils.js";
+
+const CLEANUP_TIMEOUT = 30000;
+
+/**
+ * Controls rendering of the views for pages and thumbnails.
+ */
+class PDFRenderingQueue {
+  constructor() {
+    this.pdfViewer = null;
+    this.pdfThumbnailViewer = null;
+    this.onIdle = null;
+    this.highestPriorityPage = null;
+    /** @type {number} */
+    this.idleTimeout = null;
+    this.printing = false;
+    this.isThumbnailViewEnabled = false;
+
+    if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
+      Object.defineProperty(this, "hasViewer", {
+        value: () => !!this.pdfViewer,
+      });
+    }
+  }
+
+  /**
+   * @param {PDFViewer} pdfViewer
+   */
+  setViewer(pdfViewer) {
+    this.pdfViewer = pdfViewer;
+  }
+
+  /**
+   * @param {PDFThumbnailViewer} pdfThumbnailViewer
+   */
+  setThumbnailViewer(pdfThumbnailViewer) {
+    this.pdfThumbnailViewer = pdfThumbnailViewer;
+  }
+
+  /**
+   * @param {IRenderableView} view
+   * @returns {boolean}
+   */
+  isHighestPriority(view) {
+    return this.highestPriorityPage === view.renderingId;
+  }
+
+  /**
+   * @param {Object} currentlyVisiblePages
+   */
+  renderHighestPriority(currentlyVisiblePages) {
+    if (this.idleTimeout) {
+      clearTimeout(this.idleTimeout);
+      this.idleTimeout = null;
+    }
+
+    // Pages have a higher priority than thumbnails, so check them first.
+    if (this.pdfViewer.forceRendering(currentlyVisiblePages)) {
+      return;
+    }
+    // No pages needed rendering, so check thumbnails.
+    if (
+      this.isThumbnailViewEnabled &&
+      this.pdfThumbnailViewer?.forceRendering()
+    ) {
+      return;
+    }
+
+    if (this.printing) {
+      // If printing is currently ongoing do not reschedule cleanup.
+      return;
+    }
+
+    if (this.onIdle) {
+      this.idleTimeout = setTimeout(this.onIdle.bind(this), CLEANUP_TIMEOUT);
+    }
+  }
+
+  /**
+   * @param {Object} visible
+   * @param {Array} views
+   * @param {boolean} scrolledDown
+   * @param {boolean} [preRenderExtra]
+   * @param {boolean} [ignoreDetailViews]
+   */
+  getHighestPriority(
+    visible,
+    views,
+    scrolledDown,
+    preRenderExtra = false,
+    ignoreDetailViews = false
+  ) {
+    /**
+     * The state has changed. Figure out which page has the highest priority to
+     * render next (if any).
+     *
+     * Priority:
+     * 1. visible pages
+     * 2. zoomed-in partial views of visible pages, unless `ignoreDetailViews`
+     * 3. if last scrolled down, the page after the visible pages, or
+     *    if last scrolled up, the page before the visible pages
+     */
+    const visibleViews = visible.views,
+      numVisible = visibleViews.length;
+
+    if (numVisible === 0) {
+      return null;
+    }
+    for (let i = 0; i < numVisible; i++) {
+      const view = visibleViews[i].view;
+      if (!this.isViewFinished(view)) {
+        return view;
+      }
+    }
+
+    if (!ignoreDetailViews) {
+      for (let i = 0; i < numVisible; i++) {
+        const { detailView } = visibleViews[i].view;
+        if (detailView && !this.isViewFinished(detailView)) {
+          return detailView;
+        }
+      }
+    }
+
+    const firstId = visible.first.id,
+      lastId = visible.last.id;
+
+    // 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;
+        if (visibleIds.has(holeId)) {
+          continue;
+        }
+        const holeView = views[holeId - 1];
+        if (!this.isViewFinished(holeView)) {
+          return holeView;
+        }
+      }
+    }
+
+    // All the visible views have rendered; try to render next/previous page.
+    // (IDs start at 1, so no need to add 1 when `scrolledDown === true`.)
+    let preRenderIndex = scrolledDown ? lastId : firstId - 2;
+    let preRenderView = views[preRenderIndex];
+
+    if (preRenderView && !this.isViewFinished(preRenderView)) {
+      return preRenderView;
+    }
+    if (preRenderExtra) {
+      preRenderIndex += scrolledDown ? 1 : -1;
+      preRenderView = views[preRenderIndex];
+
+      if (preRenderView && !this.isViewFinished(preRenderView)) {
+        return preRenderView;
+      }
+    }
+    // Everything that needs to be rendered has been.
+    return null;
+  }
+
+  /**
+   * @param {IRenderableView} view
+   * @returns {boolean}
+   */
+  isViewFinished(view) {
+    return view.renderingState === RenderingStates.FINISHED;
+  }
+
+  /**
+   * Render a page or thumbnail view. This calls the appropriate function
+   * based on the views state. If the view is already rendered it will return
+   * `false`.
+   *
+   * @param {IRenderableView} view
+   */
+  renderView(view) {
+    switch (view.renderingState) {
+      case RenderingStates.FINISHED:
+        return false;
+      case RenderingStates.PAUSED:
+        this.highestPriorityPage = view.renderingId;
+        view.resume();
+        break;
+      case RenderingStates.RUNNING:
+        this.highestPriorityPage = view.renderingId;
+        break;
+      case RenderingStates.INITIAL:
+        this.highestPriorityPage = view.renderingId;
+        view
+          .draw()
+          .finally(() => {
+            this.renderHighestPriority();
+          })
+          .catch(reason => {
+            if (reason instanceof RenderingCancelledException) {
+              return;
+            }
+            console.error("renderView:", reason);
+          });
+        break;
+    }
+    return true;
+  }
+}
+
+export { PDFRenderingQueue };