Gui development is broken.

This afternoon I sat down to write a mini text editor.

And I wanted to do it in OCaml. Here’s what I found.

Option 1: The Web

By far the most widely used graphics toolkit in history is HTML and CSS. It comes with its own scripting language, and tens of thousands of developers willing to lend support. Hundreds of companies exist solely to make it easier to make websites.

And it’s definitely the easiest option. It’s the first thing I learned as a programmer and it’s ridiculous how much better designed, documented, and implemented it is than all the alternatives I tried later.

But it turns out that all that power comes at some cost! It takes an enormously complex browser to render a webpage, and it’s not the most efficient situation. Atom has been widely criticized for being slow, in part due to its reliance on javascript and the DOM.

All in all, I decided I didn’t want to write or compile to javascript, and I didn’t want to have a browser as a dependency for my text editor. (I wouldn’t have been able to open new instances of the editor quickly.)

What other GUI options did I have?

Option 2: Writing to the framebuffer

I only considered this because of a really interesting blogpost that outlines writing to the framebuffer.

This strategy, writing pixels directly to the screen, is as low-level as I can imagine and I whole-heartedly support any courageous soul who attempts to write a text editor this way. I’m not sure how user-input would work; maybe reading directly from a keyboard?

One huge disadvantage to this option is that it doesn’t fit within a window manager. I wouldn’t be able to use different workspaces or alt-tab or anything. Alas! It was a fun thought.

Option 3: The Terminal

Okay, simple. You want to make a text editor, make it like vim or nano and run it in a terminal. That’s got to be easy, right?


Terminals communicate with their program through a text-based protocol and most allow everything from mouse input to colorful ascii-based animation. Specifically, terminals do a lot more than just printing text. (Refer to this fantastic talk that goes into ANSI terminals in much more depth.)

The protocol is “simple”, see, the program just outputs text and that text is rendered on the screen. Except if one of those pieces of text happens to look like \[033\[3;9H] or like /x1b[31m, in which case any number of things could happen… from changing the title of the terminal window, to requesting the mouse’s current location. But thankfully you wouldn’t have to do much stuff like that… unless you’re writing a text editor.

Plus, I’d still have to choose a terminal emulator. And terminals are not simple pieces of software. Xterm is over 65 thousand lines of code. Even suckless’s terminal is 2619 lines of code. Why so complex? Oh right, terminals use an archaic textual interface to render a program graphically.

Still don’t think that terminals expose a graphical interface? Consider alacritty, a terminal that uses the GPU to accelerate this rendering process.

You can definitely make a case for terminals and they have their place, but I don’t think calling them broken for anything more interactive than ed is at all a longshot. And writing an interactive terminal-based text editor, even a simple one, would not be easy.

Option 4: the X server

Ah the X server! (Well known for being kind and gentle.) I’ll be honest, I don’t know how the X server works or what its protocol looks like. I tried using several different OCaml bindings to Xlib, which is the main C interface to the X server.

These worked with varying degrees of success. It certainly took more than a few lines of HTML and CSS to display some colourful text. My largest issue is that any textual display supported by X11 is restricted to bitmap fonts. (Fonts that cannot be scaled up or down; each pixel is determined by the font.)

Since I have a high resolution screen, this was kind of a deal-breaker for me. Bitmapped fonts look pretty small on it. I briefly considered making my own bitmap font before taking a look into how most applications use modern, scalable fonts.

There is a library called “FreeType” that turns vector glyphs into pixels. This can be combined with a bare-bones X11 interface to create the whole glyph set and then try to draw each glyph in the right spot. I’d much rather have something do that for me…

Option 5: A Drawing toolkit!

Yes! There’s a toolkit for making drawings Cairo, more abstract than the X server, but less complicated than most GUI libraries. Cairo calls FreeType itself to render text, and gives you all the drawing primitives I would need. This works pretty well! And is probably what I will end up using. :D

But let’s say you also want a button.

A button?

Yeah, a button. Or a scrollbar. Or, dare I say, a drop-down menu? A drawing toolkit aint gonna work for long.

Option 6: A GUI library

“Why,” you say, “no need to speak to the X-server directly — there are plenty of libraries designed for just this purpose! GUI libraries!”

Yes! The best set of bindings in OCaml are LablGTK for GTK 2.

LablGTK is actually quite impressive. I believe it’s the most extensive use of OCaml objects in history. OCaml’s objects were the result of a 2002 research paper on type inference. LablGTK provided a safely-typed interface to the highly dynamic GTK API.

But GTK is so complicated! It’s great when you want to make something like Gimp, but if you just want a few buttons and some text, using GTK is like mowing a lawn with a helicopter.

And I got lucky that OCaml had this great set of bindings. What if I wanted to write a GUI in an even more obscure language? What, I’ve just got to link to C libraries and write the bindings myself? This seems a bit ridiculous.

What are we missing?

Why is this so hard? I just want low-level access to write a simple graphical interface in a somewhat obscure language.

Okay maybe I get why it’s hard.

But seriously, we’ve made lots of language-independent systems; why can’t this be one? Tons of people must want language-agnostic graphics interfaces!

I think GUI libraries are going down the wrong path. That’s not to say they don’t have a place, but they only expose a C interface. This leaves each programming language to figure out its own bindings, resulting in poor support and incomplete documentation.

We can do better:

Imagine, if you will, a procedural json interface to the screen. Run with the fictitious command graphical python

(This is similar to the web, really, but it’s procedural instead of declarative, and the scripting is done server-side.)

import json

def out(a): print(json.dumps(a))
def get(): json.parse(input())

out({command: "new_window",
     background: "black",
     title: "example!"})

window_id = get()

out({command: "new_text_box",
     border: "grey",
     content: "hi there!"})

text_box = get()

out({add: text_box, to: window_id})

out({command: "draw_triangle",
     color: "pink",
     coordinates: ... })

out({command: "pop_event_queue"})

event = get() # respond to event...

I don’t care about the particulars. Maybe not stdin and stdout. Maybe it communicates with the graphical process over sockets. Point is, I want something simpler and higher-level than X11, with a json protocol.

Imagine the advantages.

  1. All languages speak json fluently.
  2. One set of documentation for all languages.
  3. It would be lower-level and faster than manipulating a DOM, without the need for a browser.
  4. Unit testing for graphical commands would suddenly be easy.
  5. You’d get readable and searchable json for debugging.

Graphical user interfaces are truly awesome. They’re so awesome we don’t do anything without them. Let’s make them easy and fun to write.

PS. Now I really want to write GUIs with jq.
Thanks to Laura Lindsey, Paul Gowder, Tom Ballinger, Tobin Yehle, and Kevin Lynagh for their feedback on this post!

Charles, etc