[cairo-bugs] [Bug 69796] New: HiDPI scaling not working with quartz cairo_surface_create_similar() implementation

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=69796

          Priority: medium
            Bug ID: 69796
          Assignee: vladimir at pobox.com
           Summary: HiDPI scaling not working with quartz
                    cairo_surface_create_similar() implementation
        QA Contact: cairo-bugs at cairographics.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: alexl at redhat.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: quartz backend
           Product: cairo

Gtk+ 3.10 uses a back-buffer surface for doing scrolling, rather than clipping
and self-surface copying. This causes problems on the Quartz backend, because
the back buffer (created by cairo_surface_create_similar()) does not inherit
the NSWindow.backingScaleFactor of the window surface passed to
create_similar().

This means that the offscreen buffer will be a lower resolution than the actual
window resolution and when we draw it to the window it will be upscaled and
blurry.

In the cairo master cairo_surface_create_similar() already inherits the
device-scale from the other surface, and the quartz backend need to do this
similarly, by allocating a larger CGBitmap, and either setting the cairo device
scale, or pushing the device scale to a lower quartz level (CGContext?).

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