The screen grabber was a workaround for an extremely slow path in Mesa
when reading back pixel data from the frame buffer. It was using pixel
buffer objects by directly calling into GL to hit a fast blit path in
Intel's driver. This should no longer be necessary with the latest
Mesa because the normal read pixels path now has a fast path to just
memcpy the data. Using PBOs in that case just adds an extra
indirection because the data is read into an intermediate buffer and
then copied back out again.
We want to be able to remove the dependency on linking against libGL
directly from Gnome Shell because that will not work if Cogl is
actually using GLES. Also libGL includes GLX which means gnome-shell
ends up with a hard dependency on Xlib which hinders the goal of
getting Gnome Shell to be a Wayland compositor.
https://bugs.freedesktop.org/show_bug.cgi?id=46631https://bugzilla.gnome.org/show_bug.cgi?id=685915
We've been dangling on the edge of unsafety, unnoticed, for a little while
about the reference count safety of ShellScreenshot. GJS owns the entire
reference count, so as soon as it goes out of scope it could die, causing
GJS to try and fetch the corresponding wrapper object for a stale pointer.
We haven't seen any crashes because of luck -- SpiderMonkey tries to group
together deallocations to limit GC pauses, and there isn't really a lot
of GC pressure in the duration that a screenshot happens, so we tend to
be mostly stable. But in the case that you create a lot of objects while
a screenshot is going on, by hammering the "Print Screen" button, for
example, you can destroy the GObject before the callback finishes.
https://bugzilla.gnome.org/show_bug.cgi?id=672775
