Clay: a UI toolkit in CeeSafe

Clay is ClayWind ported to CeeSafe, with no C code and no dependencies. ClayWind is a Tailwind-flavoured immediate-mode UI toolkit built on the layout model of Clay by Nic Barker. The port is about 18,000 lines. It is a working example of what CeeSafe is for: a program that does everything itself, from layout to pixels, and still runs on every desktop.

What it does

• Layout: a port of Clay 0.14's layout engine, checked against the C original by a differential fuzzer. Flex rows and columns, grow and fit sizing, wrapping, floating elements, scrolling and transforms.
• Rendering: a software renderer written to match ThorVG's output.
  • Anti-aliased paths, gradients, images, shadows, blur, filters and every CSS blend mode.
  • TrueType text, read and rasterized by the toolkit itself.
• Speed:
  • Retina: frames are drawn at the display's pixel ratio.
  • Incremental: only what changed between frames is redrawn, and the result is byte-identical to a full redraw. A 2× frame costs 2–4 ms instead of 64.
• Controls: buttons, text input, sliders, tabs, dropdowns, lists, a context menu and tooltips, with focus and transitions.

What it uses in CeeSafe

• Native windows: lib/std's Window (type-system.md §26.13), with AppKit on macOS, Win32 on Windows and X11 on Linux. ClayWind's desktop host presents only the boxes that changed (Window.presentChanged). The program itself has no extern "C".
• Regions: the renderer and the UI borrow their memory from a FixedBufferAllocator, and the borrow checker tracks those loans across the whole frame.
• Generic methods and dyn interfaces: Ui.endFrame<M: TextMetrics> takes any text measurer, including the renderer's own font engine, and every host's Platform is passed as a dyn Platform.
• Hosts on the standard library: sockets and async I/O for a browser host (HTTP and WebSocket servers written in CeeSafe), and the console for a terminal host.

Several language changes came from this port, or from work it started:

• The port's own findings: generic methods, arrays of views and dyn I as a bound.
• Follow-ups: static view tables, and, found while testing them, a soundness fix for static mut and stricter rules for static in signatures.
• What the hosts needed: native windows and presentChanged.

Each has a decision record, ADRs 0063 to 0070.

Running it

With ceesafec 0.14.0 or later:

git clone https://github.com/CeeSafe/Clay.git
cd Clay/claywind-hosts/desktop
ceesafec build
./out/desktop

The same demo also runs headless (for screenshots and tests), in a browser (claywind-hosts/browser) and in a terminal (claywind-hosts/terminal). The repository's README describes each host and the test suite.