[konsole] [Bug 463600] New: Some font glyphs cast a "shadow" on the previous cell and/or render at the wrong size

[illode]

https://bugs.kde.org/show_bug.cgi?id=463600

            Bug ID: 463600
           Summary: Some font glyphs cast a "shadow" on the previous cell
                    and/or render at the wrong size
    Classification: Applications
           Product: konsole
           Version: 22.12.0
          Platform: Archlinux
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: font
          Assignee: konsole-devel at kde.org
          Reporter: illode at illode.io
  Target Milestone: ---

Created attachment 154887
  --> https://bugs.kde.org/attachment.cgi?id=154887&action=edit
Both issues on Konsole, Kitty, and Alacritty with both black and white
backgrounds

SUMMARY
Some glpyhs cast a "shadow" (aliasing?) on the previous cell. The effect is
more pronounced with small font sizes, and disappears with huge font sizes. The
top/bottom of some glyphs also don't appear to align with the top/bottom of the
cell, see the attachment for obvious examples.


STEPS TO REPRODUCE
1. Install and use a font with powerline + powerline-extra glyphs (any nerd
font)
2. Print buggy glyphs:
echo -e "nf-pl-left_hard_divider
\x1b[45m\x1b[35m\xee\x82\xb0\x1b[0m\x1b[35m\xee\x82\xb0
\x1b[0m
nf-ple-right_half_circle_thick
\x1b[45m\x1b[35m\xee\x82\xb4\x1b[0m\x1b[35m\xee\x82\xb4"
# Escape codes are: background magenta -> foreground magenta ->
'nf-pl-left_hard_divider' nerd font glyph -> reset colors -> foreground magenta
->  nf-pl-left_hard_divider  -> reset colors -> repeat using
nf-ple-right_half_circle_thick instead


OBSERVED RESULT
At font size 11 a ~1px shadow is cast on the border of the previous cell. The
second glyph(s) don't align with the edges of the previous cells.

EXPECTED RESULT
There is no shadow and the glyphs are aligned.
SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.26.4
KDE Frameworks Version:  5.101.0
Qt Version: 5.15.7

ADDITIONAL INFORMATION
Out of the 3 terminals tested, Konsole was the most jarring, with Kitty being
the only one with no visible problems.
Possibly related to bug https://bugs.kde.org/show_bug.cgi?id=453086 and merge
request https://invent.kde.org/utilities/konsole/-/merge_requests/722, although
this seems like it might be more of an aliasing issue.

Screenshot setup:
* Terminals using JetBrainsMonoNL Nerd Font Mono (works with all nerd fonts I
tested)
* Terminals using size 11 font
* Terminal windows set to be fully transparent
* Background wallpaper set to #000000 and #ffffff
* Example used #06969A as the main font color via starship to avoid having to
recreate the same color scheme in all 3. The issue applies regardless of
whether escape codes or fixed colors were used, though.

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