[Regression] The zoomLayer-functionality is broken after PR 17817

[Snuffleupagus]

Attach (recommended) or Link to PDF file

wuppertal_2012.pdf

Web browser and its version

N/A

Operating system and its version

N/A

PDF.js version

master, or any version after PR #17817

Is the bug present in the latest PDF.js version?

Yes

Is a browser extension

No

Steps to reproduce the problem

1. Load the attached PDF document in the viewer.
2. Wait until initial rendering is complete.
3. Change the zoom level to e.g. page-width. (It must be a zoom operation that triggers immediately, i.e. not using defaultZoomDelay.)

What is the expected behavior?

That the previously rendered canvas, as stored in this.zoomLayer on the PDFPageView-instance, is visible while the new canvas renders in the background.

Note that you need a fairly slow rendering page to easily spot this, which is probably why the issue has gone unnoticed.

What went wrong?

The new canvas renders visibly, which this.zoomLayer is intended to avoid (such that the page is "usable" while re-rendering occurs.)

Link to a viewer

No response

Additional context

git bisect gave the following output, i.e. this points to PR #17817:

918b500ca5075f8b03167ef276c990e6987190ca is the first bad commit
commit 918b500ca5075f8b03167ef276c990e6987190ca
Author: Calixte Denizet <[email protected]>
Date:   Thu Mar 21 12:51:08 2024 +0100

    Avoid wrong scrolling when calling zoomReset

    The goal of this patch is to fix the test:
    https://searchfox.org/mozilla-central/source/toolkit/components/pdfjs/test/browser_pdfjs_zoom.js

    It's a regression due to #17790.

 test/integration/viewer_spec.mjs       | 32 ++++++++++++++++++++++++++++++++
 web/annotation_editor_layer_builder.js |  1 -
 web/pdf_page_view.js                   |  7 ++++++-
 3 files changed, 38 insertions(+), 2 deletions(-)

/cc @calixteman