I have been away from wayland system for a while because of work, but I still remember back in the day the pain to manage the window frame (as known as decorations) in wayland system. Surprisingly quite a lot of server work shifted to client side to manage, eg, you need to implement key repeat event in the client applications.
There are two ways right now to do the client decorations.
I hate every single line of xwayland code I wrote, it is ugly, long and hard to maintain. Now I know very well why there is wayland in the first place, sadly a complete wayland compositor has to bring a piece of crap of X with it. I just finished the selection handling in xwayland by mimicing weston code. After finally understand that 1000 lines of confusing code, I just found out I can’t do any better.
In the first blog of libdrm, we went through the
repainting loop using the libdrm. Now we move on to the topic of
framebuffers. A framebuffer is a piece of memory (could be on main memory or on
GPU) for repainting every frame. It is like a canvas, represents what you would
finally see on screen. Framebuffer is already a familiar concept to rendering
programmers, in OpenGL, We have GL_FRAMEBUFFER_0 for presenting the
surface, additional framebuffers for roles like G-Buffer and
post-processing. In GPU programming, framebuffer is also a broader concept,
“abstraction of a collection of attachments”, the underlining attachments
corresponds to actual pieces of memory we talk about here.
You need a wayland compositor library to create a wayland server. Wayland is a
protocol, itself, cannot do much, long time ago I used to think the server-side
wl_resource represents some structure you can operate on, well it turned out
all you do with it is handling messages between client and server. All the logic
you need to implement yourself.
There were a few attempts to wayland compositing library created. The first sucessful one is wlc. I think its existence is that weston (the twin of the wayland project, now maintained by Pekka Paalanen). was a monolith application for a long time. Weston looks pretty and quite fast and beautiful but not very useful to anyone else. The developers maybe realized that they want to get more people to use weston, so they managed to strip libweston out of weston itself. It was a good attempt, although I doubt their true intention was to creating a reusable compositing library. Nonetheless, to some extent, it helped the birth of the third library by Drew Devault, the wlroots.
wl_data_device interface in the base wayland protocol is the most complex one,
in my opinion, wayland.xml explains it fairly well, but every pieces are
scattered in the file, here I serialize it together, give you quick run through.
In brief, data device in wayland consists of four interfaces: The first is
wl_data_device_manager, it is the global. The second is wl_data_device,
can be created from wl_data_device_manager for a given seat, it is used to
set selection(ctrl-c ctrl-v) and drag-n-drop. The 3rd is wl_data_source,
also created from wl_data_device_manager, this source will be either a
selection source or drag-n-drop source. The last is wl_data_offer, which is
used for copying data from wl_data_source.
The last post I laid out the story of me with wayland. Technology is fascinating isn’t it? Every once a while, there are plenty of new projects that aim to start an revolution, getting people excited. Projects like systemd, Wayland, Vulkan make us think how come we did not think of those before, they seemed perfect at the moment. Technologies always work like a rush of hot wave, our sights are limited at the moment we are in, maybe 5 years from now, even vulkan is not sexy anymore. For ten years, community has been urging everyone to jump on the boat of wayland. Some major platform adopted it, just there is no money in it. Major platforms like GNOME and KDE are not even mature yet, KDE developers also worries about the future of the wayland, will it last 30 years like X window?
It was a good will.
5 years ago, I read a blog about the future of linux desktop, I was using a
window manager called Awesome (one of my friend introduced it to me, I was
enchanted by how he opened two terminals side-by-side, one for coding and one
for compiling). A voice about next generation desktop was just raised in the
linux community , a group of hackers demod the weston project, where you can
rotate the application windows. They also pointed out the existing problems in
the x server architecture(basically it is too old, let us just replace it). It
is cumbersome, too many components, easily dead after package upgrade.