Painting a full-screen circle

gistfile1.dart

import "dart:sky";

Screen screen = window.screen;
double width = screen.availableWidth;
double height = screen.availableHeight;
PaintingContext ctx = new PaintingContext(width, height);
double radius = min(width, height) * .9;
Paint paint;
paint.setARGB(1, 0, 1, 0);
ctx.drawCircle(width / 2, height / 2, radius, paint);

window.rootDisplayList = ctx;