From 3402b727eeab7ae3f2ba3ebf4a97adf578efa771 Mon Sep 17 00:00:00 2001
From: Calixte Denizet <calixte.denizet@gmail.com>
Date: Mon, 9 Dec 2024 19:55:31 +0100
Subject: [PATCH] Make sure the canvas is always the first child of its wrapper

While drawing, in zooming fast enough, it's possible, intermittently, to have the canvas
after the svg which makes the svg invisible.
So this patch makes sure to have the canvas at the right position.
---
 web/pdf_page_view.js | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/web/pdf_page_view.js b/web/pdf_page_view.js
index 13b18e433c26f..83766a78ad442 100644
--- a/web/pdf_page_view.js
+++ b/web/pdf_page_view.js
@@ -975,6 +975,10 @@ class PDFPageView {
 
     const hasHCM = !!(pageColors?.background && pageColors?.foreground);
     const prevCanvas = this.canvas;
+
+    // In HCM, a final filter is applied on the canvas which means that
+    // before it's applied we've normal colors. Consequently, to avoid to
+    // have a final flash we just display it once all the drawing is done.
     const updateOnFirstShow = !prevCanvas && !hasHCM;
     this.canvas = canvas;
     this.#originalViewport = viewport;
@@ -984,7 +988,13 @@ class PDFPageView {
         // Don't add the canvas until the first draw callback, or until
         // drawing is complete when `!this.renderingQueue`, to prevent black
         // flickering.
-        canvasWrapper.append(canvas);
+        // In whatever case, the canvas must be the first child.
+        const { firstChild } = canvasWrapper;
+        if (firstChild) {
+          firstChild.before(canvas);
+        } else {
+          canvasWrapper.append(canvas);
+        }
         showCanvas = null;
         return;
       }
@@ -996,10 +1006,12 @@ class PDFPageView {
         prevCanvas.replaceWith(canvas);
         prevCanvas.width = prevCanvas.height = 0;
       } else {
-        // In HCM, a final filter is applied on the canvas which means that
-        // before it's applied we've normal colors. Consequently, to avoid to
-        // have a final flash we just display it once all the drawing is done.
-        canvasWrapper.append(canvas);
+        const { firstChild } = canvasWrapper;
+        if (firstChild) {
+          firstChild.before(canvas);
+        } else {
+          canvasWrapper.append(canvas);
+        }
       }
 
       showCanvas = null;