With Plasma 5 a change regarding auto-hiding panels was introduced. The complete interaction was moved from Plasma to KWin. This was an idea which we had in mind for a long time. The main idea is to have only one process to reserve the interaction with the screen edges (which is needed to show the panel when hidden) and to prevent conflicts there. Also it allowed to have only one place for providing the hint that there is the panel.
On an implementation level that uses an x11-property protocol between KWin and Plasma to indicate when the panel should be hidden. KWin then does the interaction to hide it and to show on screen edge activation.
Unfortunately from a visual perspective this created a regression. In Plasma 4 the auto-hiding panel was animated with our Sliding-Popups effect, but in Plasma 5 this doesn’t work any more. The reason for that is that our effect system can only animate when a window gets mapped and unmapped. With the new protocol the window doesn’t get unmapped when hidden and not mapped when shown, so our effects are not able to react on it. Technically our Client object is kept instead of being released on unmapped.
Thanks to Wayland this will be working again starting with Plasma 5.8. For Wayland windows KWin keeps the object around when a window gets unmapped and uses the same object when it gets shown again. KWin keeps more state for Wayland windows than for X11 windows. But this also means that our animations are not working for Wayland windows. Last week I addressed this and extended the internal effects API to also support hiding/showing again of Wayland windows. As the effects API does not differentiate between Wayland and X11 windows this change also enables the auto-hiding panel animation. All that was needed was emitting two signals at the right place.
Here Wayland shows another strength: not only does it help to bring features to X11 it also allows us to automate the testing. With a pure X11 system we would have had a hard time to properly auto-test this. But for Wayland we have a nice isolated integration test-framework which allowed to add a test-case for auto-hiding panels.