From af8df207bb04687b746833c93cb71342362a4d66 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Thu, 1 Jun 2023 17:44:14 +0200
Subject: [PATCH 1/2] Don't dispatch "pagerendered"-events on the *temporary*
 CSS-only zooming done when `drawingDelay` is used (PR 15812 follow-up)

We shouldn't dispatch a "pagerendered"-event when doing *temporary* CSS-only zooming, but simply wait until the actual rendering is done.
While I don't believe that this regression has caused any actual bugs, dispatching *duplicate* events is nonetheless inconsistent and should be fixed.
---
 web/pdf_page_view.js | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/web/pdf_page_view.js b/web/pdf_page_view.js
index 234f71ba8..47d6c39d7 100644
--- a/web/pdf_page_view.js
+++ b/web/pdf_page_view.js
@@ -616,6 +616,11 @@ class PDFPageView {
           hideTextLayer: postponeDrawing,
         });
 
+        if (postponeDrawing) {
+          // The "pagerendered"-event will be dispatched once the actual
+          // rendering is done, hence don't dispatch it here as well.
+          return;
+        }
         this.eventBus.dispatch("pagerendered", {
           source: this,
           pageNumber: this.id,

From a60bb5f93694ff7f8d3ff2079af8b8ebfe32d760 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Thu, 1 Jun 2023 18:46:50 +0200
Subject: [PATCH 2/2] Don't use partially rendered pages to generate thumbnails
 when `drawingDelay` is used (PR 15812 follow-up)

While it's slightly difficult to trigger in practice, unless the `defaultZoomDelay`-value is increased, it's currently possible to generate thumbnails from *partially* rendered pages when doing *temporary* CSS-only zooming.
---
 web/pdf_page_view.js | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/web/pdf_page_view.js b/web/pdf_page_view.js
index 47d6c39d7..e5f1e7eb0 100644
--- a/web/pdf_page_view.js
+++ b/web/pdf_page_view.js
@@ -125,6 +125,7 @@ class PDFPageView {
   #textLayerMode = TextLayerMode.ENABLE;
 
   #useThumbnailCanvas = {
+    directDrawing: true,
     initialOptionalContent: true,
     regularAnnotations: true,
   };
@@ -552,6 +553,7 @@ class PDFPageView {
           optionalContentConfig.hasInitialVisibility;
       });
     }
+    this.#useThumbnailCanvas.directDrawing = true;
 
     const totalRotation = (this.rotation + this.pdfPageRotate) % 360;
     this.viewport = this.viewport.clone({
@@ -605,6 +607,9 @@ class PDFPageView {
           // the rendering state to INITIAL, hence the next call to
           // PDFViewer.update() will trigger a redraw (if it's mandatory).
           this.renderingState = RenderingStates.FINISHED;
+          // Ensure that the thumbnails won't become partially (or fully) blank,
+          // if the sidebar is opened before the actual rendering is done.
+          this.#useThumbnailCanvas.directDrawing = false;
         }
 
         this.cssTransform({
@@ -1033,9 +1038,11 @@ class PDFPageView {
    * @ignore
    */
   get thumbnailCanvas() {
-    const { initialOptionalContent, regularAnnotations } =
+    const { directDrawing, initialOptionalContent, regularAnnotations } =
       this.#useThumbnailCanvas;
-    return initialOptionalContent && regularAnnotations ? this.canvas : null;
+    return directDrawing && initialOptionalContent && regularAnnotations
+      ? this.canvas
+      : null;
   }
 }