Don't update the visible canvas at 60 fps (bug 1936605)

Instead, we update the visible canvas every 500ms.
With large canvas, updating at 60fps lead to a lot gfx transactions and it can take a lot of time.
For example, with wuppertal_2012.pdf on Windows, displaying it at 150% takes around 14 min !!! without
this patch when it takes only around 14 sec with. Even at 30% it helps to improve the performance
by around 20%.

web/app.js

@@ -326,8 +326,6 @@ const PDFViewerApplication = {
       }
     }
     if (params.has("pdfbug")) {
-      AppOptions.setAll({ pdfBug: true, fontExtraProperties: true });
-
       const enabled = params.get("pdfbug").split(",");
       try {
         await loadPDFBug();
@@ -335,6 +333,12 @@ const PDFViewerApplication = {
       } catch (ex) {
         console.error("_parseHashParams:", ex);
       }
+
+      const debugOpts = { pdfBug: true, fontExtraProperties: true };
+      if (globalThis.StepperManager?.enabled) {
+        debugOpts.minDurationToUpdateCanvas = 0;
+      }
+      AppOptions.setAll(debugOpts);
     }
     // It is not possible to change locale for the (various) extension builds.
     if (
@@ -519,6 +523,7 @@ const PDFViewerApplication = {
       enableHWA,
       supportsPinchToZoom: this.supportsPinchToZoom,
       enableAutoLinking: AppOptions.get("enableAutoLinking"),
+      minDurationToUpdateCanvas: AppOptions.get("minDurationToUpdateCanvas"),
     }));
 
     renderingQueue.setViewer(pdfViewer);

web/app_options.js

@@ -299,6 +299,11 @@ const defaultOptions = {
     value: 2 ** 25,
     kind: OptionKind.VIEWER,
   },
+  minDurationToUpdateCanvas: {
+    /** @type {number} */
+    value: 500, // ms
+    kind: OptionKind.VIEWER,
+  },
   forcePageColors: {
     /** @type {boolean} */
     value: false,

web/base_pdf_page_view.js

@@ -21,12 +21,18 @@ class BasePDFPageView {
 
   #loadingId = null;
 
+  #minDurationToUpdateCanvas = 0;
+
   #renderError = null;
 
   #renderingState = RenderingStates.INITIAL;
 
   #showCanvas = null;
 
+  #startTime = 0;
+
+  #tempCanvas = null;
+
   canvas = null;
 
   /** @type {null | HTMLDivElement} */
@@ -51,6 +57,7 @@ class BasePDFPageView {
     this.id = options.id;
     this.pageColors = options.pageColors || null;
     this.renderingQueue = options.renderingQueue;
+    this.#minDurationToUpdateCanvas = options.minDurationToUpdateCanvas ?? 500;
   }
 
   get renderingState() {
@@ -71,6 +78,9 @@ class BasePDFPageView {
     switch (state) {
       case RenderingStates.PAUSED:
         this.div.classList.remove("loading");
+        // Display the canvas as it has been drawn.
+        this.#startTime = 0;
+        this.#showCanvas?.(false);
         break;
       case RenderingStates.RUNNING:
         this.div.classList.add("loadingIcon");
@@ -82,10 +92,12 @@ class BasePDFPageView {
           this.div.classList.add("loading");
           this.#loadingId = null;
         }, 0);
+        this.#startTime = Date.now();
         break;
       case RenderingStates.INITIAL:
       case RenderingStates.FINISHED:
         this.div.classList.remove("loadingIcon", "loading");
+        this.#startTime = 0;
         break;
     }
   }
@@ -100,10 +112,41 @@ class BasePDFPageView {
     // have a final flash we just display it once all the drawing is done.
     const updateOnFirstShow = !prevCanvas && !hasHCM && !hideUntilComplete;
 
-    const canvas = (this.canvas = document.createElement("canvas"));
+    let canvas = (this.canvas = document.createElement("canvas"));
 
     this.#showCanvas = isLastShow => {
       if (updateOnFirstShow) {
+        let tempCanvas = this.#tempCanvas;
+        if (!isLastShow && this.#minDurationToUpdateCanvas > 0) {
+          // We draw on the canvas at 60fps (in using `requestAnimationFrame`),
+          // so if the canvas is large, updating it at 60fps can be a way too
+          // much and can cause some serious performance issues.
+          // To avoid that we only update the canvas every
+          // `this.#minDurationToUpdateCanvas` ms.
+
+          if (Date.now() - this.#startTime < this.#minDurationToUpdateCanvas) {
+            return;
+          }
+          if (!tempCanvas) {
+            tempCanvas = this.#tempCanvas = canvas;
+            canvas = this.canvas = canvas.cloneNode(false);
+            onShow(canvas);
+          }
+        }
+
+        if (tempCanvas) {
+          const ctx = canvas.getContext("2d", {
+            alpha: false,
+          });
+          ctx.drawImage(tempCanvas, 0, 0);
+          if (isLastShow) {
+            this.#resetTempCanvas();
+          } else {
+            this.#startTime = Date.now();
+          }
+          return;
+        }
+
         // Don't add the canvas until the first draw callback, or until
         // drawing is complete when `!this.renderingQueue`, to prevent black
         // flickering.
@@ -152,6 +195,14 @@ class BasePDFPageView {
     canvas.remove();
     canvas.width = canvas.height = 0;
     this.canvas = null;
+    this.#resetTempCanvas();
+  }
+
+  #resetTempCanvas() {
+    if (this.#tempCanvas) {
+      this.#tempCanvas.width = this.#tempCanvas.height = 0;
+      this.#tempCanvas = null;
+    }
   }
 
   async _drawCanvas(options, onCancel, onFinish) {

web/pdf_viewer.js

@@ -139,6 +139,8 @@ function isValidAnnotationEditorMode(mode) {
  *   The default value is `true`.
  * @property {boolean} [enableAutoLinking] - Enable creation of hyperlinks from
  *   text that look like URLs. The default value is `true`.
+ * @property {number} [minDurationToUpdateCanvas] - Minimum duration to wait
+ *   before updating the canvas. The default value is `500`.
  */
 
 class PDFPageViewBuffer {
@@ -243,6 +245,8 @@ class PDFViewer {
 
   #eventAbortController = null;
 
+  #minDurationToUpdateCanvas = 0;
+
   #mlManager = null;
 
   #scrollTimeoutId = null;
@@ -342,6 +346,7 @@ class PDFViewer {
     this.#enableHWA = options.enableHWA || false;
     this.#supportsPinchToZoom = options.supportsPinchToZoom !== false;
     this.#enableAutoLinking = options.enableAutoLinking !== false;
+    this.#minDurationToUpdateCanvas = options.minDurationToUpdateCanvas ?? 500;
 
     this.defaultRenderingQueue = !options.renderingQueue;
     if (
@@ -1003,6 +1008,7 @@ class PDFViewer {
             layerProperties: this._layerProperties,
             enableHWA: this.#enableHWA,
             enableAutoLinking: this.#enableAutoLinking,
+            minDurationToUpdateCanvas: this.#minDurationToUpdateCanvas,
           });
           this._pages.push(pageView);
         }