[Wayland-bugs] [Bug 101436] Screen size cannot rely on wl_output scale and geometry

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101436

            Bug ID: 101436
           Summary: Screen size cannot rely on wl_output scale and
                    geometry
           Product: Wayland
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: XWayland
          Assignee: wayland-bugs at lists.freedesktop.org
          Reporter: jadahl at gmail.com
        QA Contact: xorg-team at lists.x.org

Currently, Xwayland will configure its screen and monitors given the
wl_output's it sees being advertised.

It uses the dimensions of the current mode, together with its x/y coordinate,
where each wl_output is treated as a separate monitor. The wl_output.scale
event is completely ignored.

In practice, the actual screen size and monitor sizes that Xwayland should
have, may thus be something else.

Some examples:

* A compositor may advertise a wl_output with scale 2, and have a logical pixel
coordinate space it places windows on where the content wl_output region is
also scaled by 2. Here Xwayland should treat a 1024x768 wl_output with scale 2
as  512x384 large internal monitor.

* A compositor may advertise a wl_output with scale 2 in the same way as above,
but in fact its logical representation of the output scaled with a fractional
scale, which is not advertised at all. In this case, Xwayland has no way to
know the expected screen and monitor size.

* A compositor may advertise a wl_output with scale 2, but its logical
coordinate space is always identical to the physical pixel coordinate space,
meaning Xwayland should as it does now completely ignore the wl_output scale.

To solve this, we need to introduce a protocol (Xwayland specific or not) that
communicates the logical geometry of each wl_output.

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