Lately I have been asked a lot about using Vulkan in KWin: in fact almost every blog post in the last few months has questions about it and that seems to me there is something to write about it.
So the quick tldr: I don’t have any plans on adding support for Vulkan. Over the last years I ported to so many new technologies, including at least 3 incompatible OpenGL versions. I am not looking forward to another incompatible OpenGL version (whether it’s called Vulkan or OpenGL doesn’t matter to me on that).
Now let’s look at the strength of Vulkan: going closer to the hardware and doing multi-threaded rendering. KWin still performs the rendering in the main GUI thread. Qt tried to do rendering in an off-thread for QtQuick’s scene-graph, in case of KWin we also do that in the main-gui thread. Reworking our compositor to use threading is a lot of work and would also probably improve the performance with OpenGL. Anyway as long as KWin doesn’t support threaded rendering this improvement by Vulkan is rather moot.
Now let’s look on the closer to hardware: yesterday I did a blog post on how I want to use e.g. KMS Planes to get closer to hardware and bypass the OpenGL compositing. Vulkan will allow us to perform rendering closer to hardware, but if we don’t render at all, we don’t benefit from it. Vulkan is probably more power saving, but not using the rendering will save even more.
So Vulkan can only improve when the scene needs to be rendered: e.g. when you wobble a window or spin the desktop cube. I don’t think that those effects are what we should optimize for and spend our time on and even if: there are low-hanging fruits to optimize using OpenGL, we do not yet use OpenGL 3 or 4 features to improve these effects.
Overall Vulkan looks to me like a lot of work as once again we would have to add a new compositing backend, write a new low level interaction, rewrite all shaders, etc. etc. Going to Vulkan early would mean introducing more complexity to KWin, more different code paths our users might use. It sounds like a mood exercise to do so. But I also doubt that there will be useable Vulkan drivers any time soon.
Vulkan is a great technology which will make graphics much better. But I doubt that an application like KWin is the use-case it was developed for.
Now to something else!
KDE is currently running a fundraiser for the Randa Meetings with the topic “Bring Touch to KDE!”. I personally will not participate in the Randa Meetings, but many other KDE developers will go there and we need your support for it. Please help and make the Randa Meetings possible.
