I am very happy to announce a new version of Casilda!

A simple Wayland compositor widget for Gtk 4.

This release comes with several new features, bug fixes and extra polish that it is making it start to feel like a proper compositor.

It all started with a quick 1.2 release to port it to wlroots 0.19 because 0.18 was removed from Debian, while doing this on my new laptop I was able to reproduce a texture leak crash which lead to 1.2.1 and a fix in Gtk by Benjamin to support Vulkan drivers that return dmabufs with less fd than planes.

At this point I was invested to I decided to fix the rest of issues in the backlog…

Fractional scale

Casilda only supported integer scales not fractional scale so you could set your display scale to 200% but not 125%.

For reference this is how gtk4-demo looks like at 100% or scale 1 where 1 application/logical pixel corresponds to one device/display pixel.

*** Keep in mind its preferable to see all the following images without fractional scale itself and at full size ***

Clients would render at the next round scale if the application was started with a fractional scale set…

Or the client would render at scale 1 and look blurry if you switched from 1 to a fractional scale.

In both cases the input did not matched with the renderer window making the application really broken.

So if the client application draws a 4 logical pixel border, it will be 5 pixels in the backing texture this means that 1 logical pixel correspond to 1.25 device pixels. So in order for things to look sharp CasildaCompositor needs to make sure the coordinates it uses for position the client window will match to the device pixel grid.

My first attempt was to do

((int)x * scale) / scale

but that still looked blurry, and that is because I assumed window coordinate 0,0 was the same as its backing surface coordinates 0,0 but that is not the case because I forgot about the window shadow. Luckily there is API to get the offset, then all you have to do is add the logical position of the compositor widget and you get the surface origin coordinates

gtk_native_get_surface_transform (GTK_NATIVE (root), &surface_origin_x, &surface_origin_y);

/* Add widget offset */
if (gtk_widget_compute_point (self, GTK_WIDGET (root), &GRAPHENE_POINT_INIT (0, 0), &out_point))
  {
    surface_origin_x += out_point.x;
    surface_origin_y += out_point.y;
  }

Once I had that I could finally calculate the right position

/* Snap logical coordinates to device pixel grid */
if (scale > 1.0)
  {
    x = floorf ((x + surface_origin_x) * scale) / scale - surface_origin_x;
    y = floorf ((y + surface_origin_y) * scale) / scale - surface_origin_y;
  }

And this is how it looks now with 1.25 fractional scale.

Keyboard layouts

Another missing feature was support for different keyboard layouts so switching layouts would work on clients too. Not really important for Cambalache but definitely necessary for a generic compositor.

Popups positioners

Casilda now send clients all the necessary information for positioning popups in a place where they do not get cut out of the display area which is a nice thing to have.

Cursor shape protocol

Current versions of Gtk 4 requires cursor shape protocol on wayland otherwise it fallback to 32×32 pixel size cursors which might not be the same size of your system cursors and look blurry with fractional scales.

In this case the client send an cursor id instead of a pixel buffer when it wants to change the cursor.

This was really easy to implement as all I had to do is call

gtk_widget_set_cursor_from_name (compositor, wlr_cursor_shape_v1_name (event->shape));

Greetings

As usual this would not be possible without the help of the community, special thanks to emersion, Matthias and Benjamin for their help and support.

Release Notes

• • Add fractional scale support
  • Add viewporter support
  • Add support for cursor shape
  • Forward keyboard layout changes to clients.
  • Improve virtual size calculation
  • Fix maximized/fullscreen auto resize on compositor size allocation
  • Add support for popups reposition
  • Fix GdkTexture leak

Fixed Issues

• • #5 “Track keymap layout changes”
  • #12 “Support for wlroots-0.19”
  • #13 “Wrong cursor size on client windows”
  • #14 “Support for fractional scaling snap to device grid”
  • #19 Add support for popups reposition
  • #16 Firefox GTK backdrop/shadow not scaled correctly

Where to get it?

Source code lives on GNOME gitlab here

git clone https://gitlab.gnome.org/jpu/casilda.git

Matrix channel

Have any question? come chat with us at #cambalache:gnome.org

Mastodon

Follow me in Mastodon @xjuan to get news related to Casilda and Cambalache development.

Happy coding!