From 5b50a5055932b70de33b18e6d68d73ad024d8e87 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Sun, 31 Jul 2022 13:59:37 +0200
Subject: [PATCH] Ignore too small page-canvases in `PDFThumbnailView.setImage`

It doesn't make sense to use a page-canvas that's *smaller* than the resulting thumbnail, since that causes the image to be upscaled which results in a blurry thumbnail. Note that this doesn't normally happen, unless a very small zoom-level is used in the viewer.
---
 web/pdf_thumbnail_view.js | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/web/pdf_thumbnail_view.js b/web/pdf_thumbnail_view.js
index 2cf3f6c5c..c990cc467 100644
--- a/web/pdf_thumbnail_view.js
+++ b/web/pdf_thumbnail_view.js
@@ -352,13 +352,17 @@ class PDFThumbnailView {
     if (this.renderingState !== RenderingStates.INITIAL) {
       return;
     }
-    const { thumbnailCanvas: canvas, pdfPage } = pageView;
+    const { thumbnailCanvas: canvas, pdfPage, scale } = pageView;
     if (!canvas) {
       return;
     }
     if (!this.pdfPage) {
       this.setPdfPage(pdfPage);
     }
+    if (scale < this.scale) {
+      // Avoid upscaling the image, since that makes the thumbnail look blurry.
+      return;
+    }
     this.renderingState = RenderingStates.FINISHED;
     this._convertCanvasToImage(canvas);
   }