Android

Android is the one platform where a CGO-free process cannot own a window: every path to a drawable surface goes through JNI, and JNI needs cgo. There is no wire protocol to speak instead, the way X11 and Wayland have one.

So go-widgets/android is two processes:

The Java host stands where the X server stands on Linux. Pixels travel through a memfd the application creates and hands to the host over the socket; the Go side writes RGBA_8888, which is byte for byte Android’s ARGB_8888, so the blit is a copy with no conversion, of the damaged rectangle only. Input, insets, IME text and the accessibility tree cross a framed protocol over an abstract LocalSocket.

c, err := android.Dial("my app", nil) // nil theme: toolkit.DefaultDark()
if errors.Is(err, android.ErrUnsupported) {
	return nil // not under a host
}
defer c.Close()
return c.Run(myWidgetTree())

Client satisfies window’s Backend, so an application moves between Android and the desktop back-ends without changing a line above the window — and window.Open picks it by itself when the host’s socket is there.

arm64 only

android/arm64 is the only Android target Go links without cgo; arm, amd64 and 386 require external linking. CI asserts both halves — the one that builds and the three that do not — so the day Go lifts the restriction, the build says so.

Accessibility

A screen reader would see the SurfaceView as one opaque rectangle. The host gives it a virtual view hierarchy instead: one node per accessible widget, with the android.widget.* class Android chooses its announcements from, the text, the bounds, and an activation action. The tree is pulled when something reads it, never pushed, so an app with no accessibility service attached never builds one. An activation comes back as an ordinary click at the element’s centre, through the same code a touch takes.

Touch and animation

Each touch sample reaches the tree as a touch event, then a mouse event: the first for gesture-aware widgets, the second for the many that only listen for clicks. Animated widgets advance on a frame loop that starts when something begins animating and stops when nothing does.