[Webkit-unassigned] [Bug 205187] New: [GTK] WebKitTestRunner should enable gtk-xft-rgba

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=205187

            Bug ID: 205187
           Summary: [GTK] WebKitTestRunner should enable gtk-xft-rgba
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebKitGTK
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: clopez at igalia.com
                CC: bugs-noreply at webkitgtk.org
        Depends on: 204671

When starting WebKitTestRunner we are disabling gtk-xft-rgba, and it seems that without this setting enabled Cairo ignores the fontconfig setting regarding subpixel rendering and prefers to use CAIRO_ANTIALIAS_GRAY instead of CAIRO_ANTIALIAS_SUBPIXEL.

That means that when running layout tests, the rendered of all the fonts that don't force a specific antialiasing via -webkit-font-smoothing are antialiased with CAIRO_ANTIALIAS_GRAY. However on a real use case (a desktop of a user) those fonts would be antialiased with CAIRO_ANTIALIAS_SUBPIXEL.

Other platforms (Mac) also default to CAIRO_ANTIALIAS_SUBPIXEL.

This causes the test compositing/contents-format/subpixel-antialiased-text.html to fail (after enabling support for -webkit-font-smoothing in bug 54763). Before that this test was doing nothing (passing, but not actually testing anything).

The issue is that simply flipping the bit to enable gtk-xft-rgba is problematic since it causes news thousands of failures related to the Ahem font, that seems were passing with CAIRO_ANTIALIAS_GRAY but would fail with CAIRO_ANTIALIAS_SUBPIXEL.

So, before enabling this we should always disable antialiasing for Ahem font in bug 204671


Referenced Bugs:

https://bugs.webkit.org/show_bug.cgi?id=204671
[Bug 204671] [GTK] Several tests failing after r252701 "Turn off antialiasing when rendering with Ahem, for testing"
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