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Status update, October 2022

Hi!

This month I’ve done a lot of cleanup and bugfixing in wlroots, especially in the DRM backend, the Vulkan renderer and screencopy protocol implementation. There are still a few DRM backend bugs which need to be ironed out, but we’re getting there!

Jonas Ådahl has released wayland-protocols 1.27, which features two new protocols I’ve been working on with the KDE folks. idle-notify-v1 is a standard replacement for the old KDE idle protocol we’ve been using so far. It allows clients to be notified when the user is idle for a while. This is used by swayidle to blank the screens or lock the session after a delay, for instance. Patches for wlroots, Sway and swayidle have been merged.

The other protocol is content-type-v1 and adds a way for clients to attach a content type (such as “video” or “game”) to a surface. With this, compositors can implement generic rules for all video players or all games. I plan to make this available in Sway for_window rules.

Joshua Ashton has been working on improving the way a Wayland compositor will handle Xwayland surfaces. Up until now it was using a racy mechanism, and we could indeed hit the race in gamescope. We’re working on a proper solution to fix the race: xwayland-shell-v1.

To continue with the “fix old stuff which we believe was working fine but definitely isn’t” trend, I re-implemented wl_shm in wlroots. wl_shm is the interface used by Wayland clients to share CPU buffers (as opposed to GPU buffers). Until now we were using the libwayland implementation but defects in its API makes it a better way forward to just do everything ourselves. Implementing wl_shm is fun: in particular we need to handle SIGBUS shenanigans which the client can trigger by shrinking files mmap’ed by the compositor. And signal handlers being what they are, this results in a lot of complications.

In other graphics news, I’ve been doing more kernel work. I’ve tracked down some DisplayPort Multi-Stream Transport (DP-MST) issues with Jonas and Lyude, and sent out a fix which doesn’t break Mutter. I’ll need to send follow-up patches to address a common issue: the docs and the code don’t match. I’ve also sent another patch to make it less annoying to implement explicit synchronization in Wayland compositors: a new IOCTL to allow user-space to integrate a drm_syncobj wait with an event loop.

Together with Pekka and Sebastian, we’ve continued out work on libdisplay-info. A new website contains documentation (built via gyosu), more DisplayID bits and GTF mode generation have been merged, and Pekka is working on the high-level API.

Another unrelated small improvement worth mentioning: goguma now supports UnifiedPush! Google Play Services no longer are a required dependency to get support for push notifications.

The NPotM is go-jsonschema, a Go code generator for JSON Schema. JSON Schema can describe the structure of JSON documents, and go-jsonschema will generate matching Go structures. This is useful to avoid maintaining glue code for each and every JSON consumer. I plan to write a C code generator as well. Right now go-jsonschema can handle almost all of the drm_info schema, however many features are still missing and schemas need to be written in a specific way to make the most of go-jsonschema.

See you next time!


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