[Libreoffice-bugs] [Bug 139296] scrolling document canvas down & up can cause a line of text to "tear" with loss of registration, it clears when the line moves out of view far enough or view passes to a new page

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=139296

--- Comment #50 from spokanemagneto at gmail.com ---
Significant new clues on the text tearing issue when scrolling or editing text: 
    • It does not seem to occur with the zoom factor set to ≤100% (with or
without the sidebar displayed).
    • It does randomly occur with the zoom factor set to >100% (with or without
the sidebar displayed).
    • It does occur with the zoom factor set to Fit Width (156% with the
sidebar hidden, or 117% with the sidebar displayed). The former is my usual,
preferred setting, as per all my previous postings on this issue.
    • It does occur, albeit far less frequently and far less dramatically, with
the zoom factor set to Optimal (197% with hidden sidebar), but it also does not
seem to occur under those conditions with the sidebar displayed (148%).

The last three points are curious. Why would enlarging the workspace to Fit
Width (156% with the sidebar hidden, or 117% with the sidebar displayed) cause
the issue but using the Optimal setting (197% with the sidebar hidden, or 148%
with the sidebar displayed) seem not cause it?

Verified previous means of manifesting the problem:
    • It can be replicated most easily by using the scroll up/down buttons,
although it also does it using the scroll bar grab handle, the mouse scroll
wheel, and/or the laptop touch pad.

Verified means of correcting the torn text problem (not a fix, a band-aid):
    • It can be made to correct itself by clicking on either the Toggle
Automatic Spell Checking or Toggle Formatting Marks buttons, Reloading the
page, scrolling the page up/down until the damaged text is off-screen, or by
Viewing the sidebar if it was previously hidden.

Means of seemingly limiting the frequency and severity of the issue (not a fix,
a band-aid):
    • Do not use the default templates in the United States because the
templates use A4 paper instead of the correct Letter size (8½ ʺ×11ʺ). This was
another reported bug that has yet to be addressed.
    • Do not use the Page Format Margins setting of Normal (0.75ʺ) because the
right margin is inexplicably set to 0.79ʺ instead of 0.75ʺ. This bug was
reported as part of the aforementioned one about the Letter size issue.
    • Increase the font size above 10 point.
    • Increase the line spacing beyond the preset single or 1.15 settings
(prefer using the Fixed Custom Line Spacing to be at least 2 pts > the font
size).
    • Do not use the bizarre, non-integer default Heading sizes (e.g., Heading1
of 18.2 pt and Heading2 of 16.1 pt). Instead, use integer (non-fractional) font
sizes and line spacing.
    • Do not use Smooth Scroll as it operates opposite of what’s indicated by
the checkbox. This was 100% repeatable under the circumstances I indicated in
yet another bug report, but it was dismissed as unverifiable. In this case, it
seems to have a minor affect on the text tearing as well, as without it the
problem seems to occurred less frequently and produces far less distortion of
the characters. 

So, the overall analysis seems to be that the larger the zoom setting, the
worse the problem gets—except most notably when using the Optimal setting. It
may be that the problem exists with negative zoom increments, but it’s simply
too hard to see. Also, the larger the font size and line spacing the less
frequent and severe the issue seems to be. Other factors, as outlined in the
bullet list directly above, may also play some role in the occurrence and
repeatability of the issue.

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