Windows desktop PDF viewer scrolling lag & Local fixes

What version of the Codex App are you using (From “About Codex” dialog)?

26.915.31029

What subscription do you have?

ChatGPT Pro 20x

What platform is your computer?

Microsoft Windows 11 x64

What issue are you seeing?

When scrolling with mouse or dragging the sidebar quickly in PDF viewer, the pages are being loaded slowly. Since the page loading is being delayed, sometimes the PDF reader would show no page (i.e., Codex theme colour) or blank page. The PDF reading experience is much worse than that in Adobe Acrobat Reader. Therefore, I asked Codex to fix the problem for a smoother PDF viewing experience.

What steps can reproduce the bug?

Simply use scrolling wheel on your mouse to scroll a (large) PDF file, or drag the sidebar quickly up and down to reproduce the laggy feeling.

Additional information

I used Codex to fix the problem. Below is a version I feel comfortable to work with Codex and has been patched for my own local Codex client.

Final reporter submission: V2.4 (local S2.4)

All earlier submissions, including S2 and held-image variants, are withdrawn
as current proposals and superseded by V2.4. Older GitHub revisions may remain
accessible for history; they are not the recommended implementation.

• Final V2.4 submission
• Frozen V2.4 original source, tests and limitations

The reporter approved the current integrated reader for shipping and requested
this replacement submission. This is not an official OpenAI release or a claim
of maintainer acceptance. Keep the issue open pending product resolution.

Environment and reproduction

• Windows desktop package OpenAI.Codex 26.908.4834.0, x64.
• A 221-page illustrated A4 PDF, approximately 46 MiB; private document omitted.
• Rapid scrolling, scrollbar dragging, reversals and repeated Next/Previous
  could produce blank intervals, delayed presentation and high CPU activity.
• Selection, links, annotations and Ask for change must remain available;
  rewriting the PDF is not a remedy.

Open a long illustrated PDF, rapidly navigate in both directions, then stop and
check selection, links and annotation actions. Test cold loading separately
from a prepared cache. Also test direct page entry, Enter/Escape, invalid bounds
and preservation of the final reading position after closing/reopening.

Final proposal and evidence boundary

Use native continuous scrolling of persistent page canvases. Coalesce obsolete
scroll and navigation bookkeeping, retain prepared pixels, prioritize visible
pages, preserve annotation contracts, and provide editable direct page entry.
There is no held-image/front-buffer overlay. The existing four-process rendering
pool was retained; V2.4 does not introduce another backend or GPU experiment.

The frozen public bundle contains seven original helper modules, eight portable
synthetic test files, a README, test summary and file hashes. Its test summary
provides the exact reproducible public result. A separate local packaging check
passed 87 focused navigation/input tests. Historical tests have different scopes
and are not additive. Qualitative reporter acceptance is not a cross-device
benchmark, guaranteed rendering latency or an end-to-end annotation audit.

No private PDF, document hash, screenshots, recordings, transcripts, raw logs,
credentials, machine paths, extracted app source, app archive, privileged IPC
or installer is published. The helpers are for source-level maintainer review,
not a standalone reader. Prepared with Codex assistance; official adoption,
licensing review and release timing remain maintainer decisions.

Start with the PDF viewer entry points and the frozen V2.4 bundle linked in the issue, including its seven helper modules and eight portable synthetic test files. Reproduce rapid scrolling, dragging, navigation, direct page entry, invalid bounds, and reopen behavior on a long PDF; done means smooth continuous presentation while preserving selection, links, annotations, and Ask for change.