Chart

I’m starting, or more specifically re-starting, a project that I envisioned a couple years ago. In some of the apps I’ve created, I’ve found it useful – sometimes critical to what I want – to provide small charts (visualizations) of data from the app. One example of this is a series of histograms that show the network latencies to each step in a route from my machine to a location on the internet. There’s some great CLI tools that display the raw data in a terminal window (mtr, if you’re curious), but I think it’s easier to understand viewing the data as a series histograms. In the case of mtr, you can see where network traffic slows down or doesn’t get past.

Looking at the example above, you can see a fairly consistent latency through to the end point, with the majority of the variability at that first step (in this example, it is my wifi router hub). The down side is that the code to display just that – not even getting to labels, axis, etc – was pretty heavy.

A year ago, I tried coming up with drawing this kind of graph in SwiftUI, including displaying axis and labels. Turns out that with SwiftUI’s constraints, and the “every expanding” side effect of using GeometryReader in a SwiftUI layout, it was darned tricky to get it working. I got something working, on which I could overlay SwiftUI shape objects with explicit offsets. The downside was that it wasn’t flexible and small changes could break the layout dramatically. Last year, Apple updated SwiftUI with Canvas, which I used when generating the series of histograms above. That really opened the doors for me. Now I’d like to do the same using a SwiftUI like syntax. It seems like it would be a natural fit, and it would make creating those little sequences of visualizations a hell of a lot easier.

I know there’s other charting libraries out there – and good ones. The “ole standby” that many people use is Daniel Gindi’s Charts, but even a quick search on Swift Package Index shows other folks offering their own takes on some of these libraries, several of which are interesting for the number of stars they’ve collected. (Majid’s SwiftUICharts in particular looks interesting to me, fits in well with SwiftUI, and appears to be stable).

I’ve cobbled previous charts and plots with anything from Excel to using the D3.js library in javascript (which is a really amazing library). That background had me following a trend towards describing charts more declaratively, which fits in well with how SwiftUI works. I dug into Observable’s Plot and the Vega-lite project, and the research papers behind them. Both of have a very declarative style of describing a chart, the style of which fits in wonderfully well with the kind of declarative syntax that SwiftUI uses. Seeing what I can do to enable that kind of functionality, but using Swift, is what I’m after, and what I’d really like to be able to use.

Part of my goal in setting this up is to learn the “ins and outs” of what it takes to enable this kind of thing using result builders. I don’t feel like have a solid understanding right now, and the way I learn best is by doing – so I’m aiming to learn and do in public. I’d like to work out how to tell someone else how they could solve this kind of problem, and right now I’m far from it. I’m guessing the solution likely includes not only result builders, but careful use and design with generics and protocols as well. I’m planning on writing about my development process (and my learning!) as I tackle this. Rather than waiting for when it’s all “good and done” (assuming I get there), I have set this up to develop completely in the open. I do expect it’ll get messy, and it may never come to anything, but I figured it was worth a shot.

If you think tackling something like this might be fun, or just want to poke your head in to watch how I tackle it, you’re welcome to join in. I would love to have others to bounce ideas off of, or help with the coding if you’re so inclined. If you’re interested in following along, I’m starting with some of Github’s community tools on a repository. I set up an organization called SwiftViz, and made the repository Chart to house this project. I’ve enabled Chart Discussions – no idea how well or crappy that will work out – as a starting point. I do expect to evolve as it goes. I thought about just writing about the efforts on this blog, but a blog doesn’t really end up being very interactive – can’t have much of a discussion on it – and I’d like to at least entertain the possibility that someone else might want to collaborate with me on this.

It’s early days, and it will undoubtably get messy, but if you’re interested, drop into the repository discussions and say hello, or reach out to me on twitter if that’s easier.