denise-macos

An embeddable Cocoa view backend for Denise, a direct-rendering UI toolkit in Rust for embedded Linux and systems without a desktop environment.

Not a way to ship Denise on a Mac. denise-winit already previews on one, and a desktop application should use a desktop toolkit. This exists for the same reason the Win32 control does: an existing Cocoa application that wants a Denise panel inside it, next to its own views, with the host owning the window and the run loop.

# #[cfg(target_os = "macos")]
# fn demo() -> Result<(), denise_macos::Error> {
use denise::Size;
use denise_macos::ViewSurface;

// The host has a view; Denise has a surface the size of its backing store.
let mut surface = ViewSurface::new(Size::new(800, 480), 2.0)?;
# let _ = &mut surface;
# Ok(())
# }

DeniseView is the NSView subclass, ViewDelegate is what the host implements to drive it, and ViewSurface is the denise::Surface behind a layer-backed context.

What is different from the bare-metal backends

• The host owns the run loop. There is no run function here. AppKit decides when to draw and Denise answers — the opposite of the DRM backend, where Denise decides and the display follows.
• Damage is real. setNeedsDisplayInRect: genuinely limits what gets composited, unlike a page flip where the whole buffer goes regardless. So the rectangles the tree produces are worth passing on rather than rounding up to the whole view.
• Points are not pixels. A Retina view is 2 physical pixels per point. Denise lays out in physical pixels throughout — the conversion happens once, at this edge, and nothing above it needs the scale factor to hit-test.
• There is already a cursor. The host's window system draws one, so the composited sprite stays off: Ui::show_cursor(false), a decision that sticks rather than one the next mouse move overrides.

Platform

macOS only; elsewhere the crate compiles to almost nothing. Built on objc2, so the Objective-C bridging is checked rather than hand-rolled. unsafe is necessarily permitted here; every block carries a // SAFETY: comment.

examples/embed.rs is a complete host — a window, a view and the run loop:

cargo run -p denise-macos --example embed

Where this sits

Wraps denise-ui. The Windows equivalents are denise-win32 and denise-activex.

Status

M5 complete, run on real hardware. Part of Denise — see the repository README for the whole picture.

MIT licensed.