Architecture
About 34,000 lines of Zig on top of a thin C layer. The rule that shapes everything: the UI never changes data directly.
Data flow
UI → Action → app → Command → gateway → Event → Store → UIThe UI only reads the Store and requests actions. The app turns them into commands for the gateway, which runs on its own thread, and events come back through a queue into the Store. That's why swapping the demo gateway for the real one doesn't touch the UI.
Source tree
src/
core/ pure data, no window: types (snowflakes), Store, markdown, events,
inbox, saved messages, filters, search queries, cache format
net/ the real gateway (Discord) and the demo one, queues, voice,
settings protobuf, message cache, proxy, media URLs
theme/ KDL parser, colors, theme loader, layout engine, manager + inotify
ui/ components, rich text, palette, settings, animations, images, video
plugins/ the Lua engine and its host
platform/ window, renderer, waking the loop, FFmpeg loading. The only
place that knows about SDL's windowing
themes/ the built-in themes (also compiled into the binary)
third_party/ vendored code: Dear ImGui, dear_bindings, Lua, stb_image, libdave,
MLSpp, nlohmann/json
tools/ QA, memory benchmark, screenshots, logo and site generatorsThreads
| Thread | When it exists | Job |
|---|---|---|
| UI | Always | The main loop, sleeping in SDL_WaitEvent when nothing happens |
| Plugins | With a plugin on | All Lua runs here. It talks to the UI through two queues and sleeps when nothing happens |
| Gateway | With a token | WebSocket with heartbeat, RESUME, zlib-stream and reconnects, plus REST, one request at a time |
| Demo gateway | Without a token | Fake servers, people and messages |
| Media | Always, mostly asleep | Downloads and decodes images at low priority, at most 2 decodes at a time |
| Theme watcher | Unless disabled | Waits on inotify for changes to theme files and pywal colors |
| Video | While playing | One thread downloads, another decodes into a 3-frame ring |
| Voice | During a call | Voice gateway, UDP, Opus and DAVE |
Talking to Discord
The gateway uses WebSocket (v=10, JSON, zlib-stream) with heartbeat, session RESUME and reconnects. It connects the way the web client does. REST handles history, sending, editing, deleting, reactions and "typing", one request at a time and respecting rate limits.
The rendering
Everything is drawn with Dear ImGui's ImDrawList over SDL_Renderer, and FreeType renders the text. ImGui is an immediate-mode library, so its usual cost is redrawing all the time. Here, the loop only draws when something changes:
- Input, network, inotify and the clock wake the loop through events.
- Animations ask for frames only while they're running.
- Lists use binary search to find the first visible item and draw only what's on screen.
- Markdown is parsed once, when the message arrives, with a height cache per width.
Themes as data
A theme is parsed into colors, styles and a tree of nodes. The layout engine computes rectangles from row, column, stack, flex and sizes, then a table in src/ui/root.zig maps component names to draw functions. A component it doesn't know appears with a red border and the file's line number.
Writing themes documents the language, and the playground on the home page lets you try it in your browser.
How it stays light
See Performance.