A long long time ago, when a program wanted to draw something to the screen, it could just write to a certain spot in RAM. The screen was a wild west and anyone could draw anywhere anytime.

Nowadays, display access is coordinated by a special program called the Display Server, which "coordinates the input and output of its clients to and from the rest of the operating system, the hardware and each other". With input being mouse/keyboard/etc and output being graphics, images, anything you see in a "window".

On modern linux, for display servers most systems use either the Wayland (protocol) or x11. We're going to focus on Wayland, mostly because it's newer and there are systems in place to run older x11 apps in wayland for backwards compatibility.

Notice that it's Wayland protocol not wayland display-server. That's because Wayland is not a display server. It's a protocol; it'a a way for programs to communicate to a hypothetical display server. When people say that their system is running Wayland, what they really mean is that their system is running a display server that speaks the wayland protocol.

What's even better is that Wayland does not have a set Rendering Model, the programs decide entirely on their own how they will draw their "windows" or other graphics, then they just hand it over to the display server.

The wayland protocol actually has no opinion on what you do with the graphics the programs give you. Sure, they probably expect that you will use Kernel Mode Setting, but really if you wanted to, you could print out the graphics and give them to a league of crochet grandmas to individually tie together every single pixel into the afghan of legend! The programs would never be the wiser.

Again, the main benefit of wayland is that the programs don't care how they get input as long as it gets input, and it doesn't care what happens to its output.

So, this means we can do anything we want, so let's output to the terminal!

I take the output given to us by the client and convert the images to terminal output, the utf8 characters with ansi escape codes via the chafa library. For input, I take the keyboard and mouse (yes terminals support mice) from the stdin. And that's it! Of course, there are about 10K lines of code needed to actually do this in practice, but if you're interested in that I invite you to check out the source code.

I have many other crazy ideas of what else to do custom wayland display server, so stay tuned.