1868308 - Unexpected text selection offset in plain text and view-source mode when viewing very-long lines

Status: RESOLVED DUPLICATE of bug 1827778

(Core :: Layout: Text and Fonts, defect)

Description

[Zhai Can]

Attachment: Screenshot_2023-12-05_17-01-17.png

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:120.0) Gecko/20100101 Firefox/120.0

Steps to reproduce:

1. Goto view-source:https://raw.githubusercontent.com/MaoJianwei/eAIP-2015-Nr.13/master/Download_eAIP_2015_Nr.13.py
2. Drag the bottom scrollbar to the end, and the right scrollbar to about the mid.
3. Select some text.

Actual results:

The actual selected text is not as the page displays. See the screenshot attachment.

Also, the selection is of a wrong offset. Notice the "进" character in the screenshot.

The long line actually ends with .encode("utf-8"), but the page shows incorrectly, like the line is truncated.

Expected results:

Not so.

Additional info
If "Wrap Long Lines" in the right-click menu is enabled, things will become normal.

Issue is also present in plaintext viewing mode:

1. Save that py file
2. Change its extension to .txt
3. Set plain_text.wrap_long_lines config to false
4. Open the txt file
5. Do the same as the above

Tested Firefox versions: 120.0.1 and 122.0a1.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Layout: Text and Fonts' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Jonathan Kew [:jfkthame]]

This is a known issue where text display starts to become inaccurately positioned when the page is extremely wide and/or tall. Dup'ing to bug 1827778, which specifically talks about selection issues, though there are other related reports as well.