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  1. Qt
  2. QTBUG-95336

CFF fonts appear emboldened on high-resolution displays due to stem darkening

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Details

    • Bug
    • Resolution: Unresolved
    • P2: Important
    • None
    • 5.9, 6.2.0 Beta1
    • GUI: Font handling
    • None
    • Linux/X11

    Description

      Since Qt 5.9, Qt enables Freetype's "stem darkening" of CFF fonts (https://code.qt.io/cgit/qt/qtbase.git/tree/src/gui/text/freetype/qfontengine_ft.cpp#n151). This may improve rendering on low-resolution displays, but makes fonts appear emboldened on high-resolution displays. It should thus be enabled on low-resolution displays only in my opinion.

      Normal rendering without stem darkening:

      Artificial emboldening by Freetype's stem darkening:

      The Freetype documentation also states that stem darkening is intended for low-resolution displays, see  https://www.freetype.org/freetype2/docs/reference/ft2-properties.html:

      Stem darkening emboldens glyphs at smaller sizes to make them more readable on common low-DPI screens when using linear alpha blending and gamma correction, see FT_Render_Glyph.

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        1. 288dpi_1170.png
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          Joshua Krämer
        2. 288dpi_1171.png
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        3. 96dpi_1170.png
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          Joshua Krämer
        4. 96dpi_1171.png
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        5. comparison.png
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          Joshua Krämer
        6. image-2021-07-22-23-52-35-073.png
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          Joshua Krämer
        7. image-2021-07-22-23-52-46-523.png
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          Joshua Krämer
        For Gerrit Dashboard: QTBUG-95336
        # Subject Branch Project Status CR V

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            esabraha Eskil Abrahamsen Blomfeldt
            jkraemer Joshua Krämer
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            Dates

              Created:
              Updated:

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