Re: Heads-up: Potentially breaking changes to the GDK drawing model pushed

["Jasper St. Pierre" <jstpierre mecheye net>]

Hey everyone again

I wasn't expecting this much fallout from the change. I was hoping most of the GTK+ applications were only using widgets and draw signals. I was wrong.

I've effectively pushed a revert of these changes:

https://git.gnome.org/browse/gtk+/commit/?id=984e811c16891cb4945a090bea8ec9e81ce3dba6
https://git.gnome.org/browse/gtk+/commit/?id=24b9e91f470d2f355c6e19013f302295151baacf

Note that gtk_widget_set_double_buffered is still deprecated, and calling gdk_cairo_create outside of a begin_paint_region / end_paint is still considered legacy and isn't guaranteed to work on any backends other than X11. Everything should be functioning correctly. So, we're choosing to make these things work for X11, but new backends like Wayland, Broadway and Mir might not work with them.

If your application still has flickering or prints runtime warnings or crashes, *please* let me know. We should be back to where we were beforehand, but things do sometimes slip through the cracks.

Thanks to everyone who gave me feedback -- it's been a frustrating past few days for everyone, and I'm sorry for the breakage I caused. I have a much better handle on the situation now and the way applications are using our toolkit.

If you have any other feedback about modern drawing in GTK+, please let us know. We're always trying to support application developers, even if it may not seem like it, and if our existing APIs aren't suiting your use cases, we need to know.

On Fri, Jun 20, 2014 at 9:00 PM, Jasper St. Pierre <jstpierre mecheye net> wrote:

To better support Wayland with fewer copies and less drawing artifacts, I've pushed some potentially breaking changes to GDK, namely around gdk_cairo_create and gdk_window_begin_paint_region.

https://git.gnome.org/browse/gtk+/commit/?id=d48adf9cee7e340acd7f8b9a5f9716695352b848
https://git.gnome.org/browse/gtk+/commit/?id=be30e440c350f0f3e0f2572f7f3eab54ef96af0e

With these changes, it is now illegal to call gdk_cairo_create outside of a begin_paint / end_paint. This was always sketchy, and would never work on Wayland anyway. If your code does this, we will print a warning and return a dummy surface which won't ever be composited back into the main surface.

Additionally, it is now forbidden to call gdk_window_begin_paint_region more than once. Previously, the code had a "paint stack" which tracked paints, but since GTK+ never used this codepath it was never actually tested and was indeed broken on Wayland due to the way the Wayland backend was written. Again, we will print a warning in this case and return.

As part of these changes, gtk_widget_set_double_buffered was deprecated and removed. Again, it will never work on Wayland, as that is natively double-buffered, and it would simply break there.

I tested with some local big applications like Ardour and the GNOME applications, but don't have a GTK+3 build of Firefox, LibreOffice, Eclipse, or any big GTK+ apps like Inkscape or The GIMP.

Please double-check to make sure your apps still work fine. If you have a problem with any of this or I broke your apps by accident, please reply and I'll try to fix it.

Thanks!

--
  Jasper

--
  Jasper