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UXAndroidGraphics

UXAndroidGraphics is the Android realization of UXGraphics.

#use <UXKit>            // or #import "UXAndroidGraphics.xc"

The Canvas of the draw in flight

Section titled “The Canvas of the draw in flight”

The operations act on the android.graphics.Canvas for the current draw, reached through JNI in libUXAndroid.c.

Incoming coordinates are bounds-relative, and the bound origin makes them absolute. Android’s Canvas grows y down, so nothing needs flipping. The same is true on cairo, Canvas2D and UIKit.

Two Canvases, one vocabulary

Section titled “Two Canvases, one vocabulary”

The drawing surface is not always a window:

UXDrawView.onDrawthe real thing, on screen
the offscreen Bitmap rigthe same drawing, into a buffer that can be read back

The vocabulary does not know which surface it has. Both are a Canvas, so the same code path produces the pixels in either case.

This allows visual checking on Android without a screen: draw into a Bitmap, read it back, and compare. If offscreen rendering used a different path, the checks would test something other than what ships.

Every call crosses JNI

Section titled “Every call crosses JNI”

Unlike the in-process vocabularies, each primitive here is a JNI call. Each call has a real cost, so the primitive set is small and coarse: fill a rectangle, fill a polygon, draw text, draw a line.

A protocol with a per-pixel or per-vertex entry point would be unusable across this boundary. Designing for the narrowest backend keeps the same protocol viable on all of them.

UXCanvasGraphics has the same constraint, with a wasm-to-JS boundary in place of native-to-Java.

It strokes natively

Section titled “It strokes natively”
strokesNatively()      // true

Canvas strokes paths with joins and caps, so a path goes to it directly and not through the neutral offsetter. Arrowheads stay neutral, as on every backend.

See also

Section titled “See also”