[Libreoffice-bugs] [Bug 134275] New: Skia: Windows ClearType settings not observed causing poor font rendering

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=134275

            Bug ID: 134275
           Summary: Skia: Windows ClearType settings not observed causing
                    poor font rendering
           Product: LibreOffice
           Version: 7.0.0.0.beta1+
          Hardware: x86-64 (AMD64)
                OS: Windows (All)
            Status: UNCONFIRMED
          Severity: minor
          Priority: medium
         Component: graphics stack
          Assignee: libreoffice-bugs at lists.freedesktop.org
          Reporter: josh.lackey at gmail.com

Description:
Color subpixel antialiasing with Skia+Vulkan rendering is inaccurate on BGR
ordered display, making text difficult to read. 

Steps to Reproduce:
1. Options > View > Graphics Output > Use Skia for all rendering CHECKED
2. Have a display that is not compatible (i.e. BGR) with the default settings
Skia assumes

Actual Results:
All text rendering, including UI elements as well as in documents, lacks
clarity due to being iridescent around the edges

https://i.imgur.com/nJS9ntK.png

Expected Results:
Fonts should render the same with Skia as they do with "Use Skia for all
rendering" unchecked

https://i.imgur.com/CU9Uj6Z.png

The differences in the screenshots will either not be apparent or seem
*reversed* on a typical RGB monitor. e.g. on a standard RGB screen, the Skia
*off* might appear iridescent or blurry, while Skia *on* look fine. Trust me
when I say that is not the case on my display!

For more info see: http://www.lagom.nl/lcd-test/subpixel.php


Reproducible: Always


User Profile Reset: Yes



Additional Info:
Technical note: 

Skia requires a preprocessor directive in order to read the ClearType
parameters from system settings, which includes pixel order as well as contrast
and gamma.

https://skia.googlesource.com/skia/+/refs/heads/master/src/ports/SkTypeface_win_dw.cpp#395

https://docs.microsoft.com/en-us/dotnet/framework/wpf/advanced/cleartype-registry-settings

This might explain the SK_GAMMA_APPLY_TO_A8 issue described in this commit:

https://cgit.freedesktop.org/libreoffice/core/commit/external/skia?id=1ad3f6b8d9e0ef1e921c3ed5526ea352d67265cf

Adding #define SK_FONT_HOST_USE_SYSTEM_SETTINGS 1 to config_skia.h.in would
probably solve the issue.

https://cgit.freedesktop.org/libreoffice/core/tree/config_host/config_skia.h.in

Then the user could tune the level of ClearType antialiasing using Windows
built-in the "Adjust ClearType Text" Control Panel applet if it was not
satisfactory. However, Windows usually sets the correct subpixel order by
default.

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