https://bugs.kde.org/show_bug.cgi?id=497819
Bug ID: 497819
Summary: Full hinting (byte code interpreter) for fonts does
not work
Classification: I don't know
Product: kde
Version: unspecified
Platform: Fedora RPMs
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: unassigned-b...@kde.org
Reporter: and...@eastfarthing.com
Target Milestone: ---
Created attachment 176842
--> https://bugs.kde.org/attachment.cgi?id=176842&action=edit
FontForge source for a TTF test font with byte code hinting instructions to
clearly test hinting
SUMMARY
When I select full hinting from the Fonts panel in System Settings, KDE
applications do not actually appear to use full hints, or at least not to use
the hints in the byte code within TTF fonts.
STEPS TO REPRODUCE
1. Use the System Settings to set hinting to full
1a. Verify that /etc/fonts/conf.d is set to full hinting
1b. Verify that ~/.config/fontconfig has nothing that overrides this
2. Run KDE Plasma on Wayland
3. Set Konsole, Kwrite, or other to KDE app to use a TTF font that includes
byte code instructions for hinting (e.g., attached)
OBSERVED RESULT
The KDE app does not display text with hinting according to the byte code
within the font. Strongly-hinted fonts still appear blurry.
EXPECTED RESULT
KDE apps display text with hinting using the byte code within the font.
SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 41
KDE Plasma Version: 6.2.4
KDE Frameworks Version: 6.9.0
Qt Version: 6.8.1
Kernel Version: 6.12.5-200.fc41.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 32 × AMD Ryzen 9 7950X 16-Core Processor
Memory: 62.5 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 4090/PCIe/SSE2
ADDITIONAL INFORMATION
I first noticed this when I realized that Konsole, when set to my own coding
font, was not using the hinting instructions that I had laboriously programmed
in. This was despite hinting being set to Full in the System Setting,
/etc/fonts/conf.d/ being set to full hinting, ~/.Xresources being set to
Xft.hintstyle: hintfull, and everything else that I could think of.
Graphical Emacs, built against GTK3 and using XWayland, correctly renders the
full hinting. The FreeType tool, ftview, also correctly displays fonts with
byte code hinting, so this does not seem to be at the level of FreeType.
Since the effect of font hinting can be subtle, I have created the attached
test font to clearly verify whether byte code hinting is working or not. It
has two glyphs:
- The `x` glyph has a glyph outline that displays an N (for not hinting), but
uses byte code instructions to reposition the diagonal to a horizontal stem,
making an H to demonstrate that byte code hinting is working.
- The `o` glyph displays three nested squares. If byte code hinting is
working, each square and the spaces between them should be exactly one pixel in
thickness, regardless of font size. (There may be some variation here
horizontally depending on sub-pixel alignment settings, but certainly they
should be aligned vertically to the pixel grid.) Otherwise, if the squares are
significantly thicker than a pixel at larger sizes, byte code hinting is not
working.
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