`Image fromView:` and `Image fromScreen` fails in XWayland sessions

[Jan Vrany]

When running Smalltalk/X under Wayland (via XWayland since there's no native Wayland support yet). reading the contents of a screen or of a (smalltalk) window fails. To reproduce:

Image fromScreen

Image fromView: Transcript topView grab: false

The problem is that ​XGetImage() fails with BadMatch. It seems that XGetImage() is simply not supported by XWayland [1].

To capture whole screen (i.e., to support #fromScreen:) under GNOME we may use D-BUS interface to generate a screen capture to a .png and read it back [2], [3], [4]. Under KDE or other Wayland compositors, who knows...

[1]: ​https://github.com/LibVNC/x11vnc/issues/5
[2]: ​https://github.com/LibVNC/x11vnc/commit/528baf729f300de12c963e09d509d29d4f44ec1f
[3]: ​https://mail.gnome.org/archives/commits-list/2013-January/msg00410.html
[4]: ​http://www.matthew.ath.cx/misc/dbus

[Jan Vrany]

More resources on the problem:

[1]: ​https://fedoraproject.org/wiki/How_to_debug_Wayland_problems#Screen_capture_is_not_available_with_usual_apps
[2]: ​https://www.reddit.com/r/linux/comments/3y786p/eli5_why_wont_screen_recording_and_screenshot/
[3]: ​https://github.com/kwhat/libscreenshot/tree/master/src

[Jan Vrany]

Since XGetImage() is not supported at all by XWayland by design,
capture the screen we have to use compositor-specific way. Sigh.

Commit 8599cc6c703d/stx.libview added support for GNOME Shell
using external dbus-send command.

This is a temporary solution to keep going, we should have
proper DBus support and use that. We also need to test other
environments and properly reify desktop environment.

Since this is a workaround, I keep the ticket open but no longer
schedule it to 8.0.0 since it no longer "crashes".