canvas绘制椭圆

canvas和paiter搭配使用；

class DrawPainter extends CustomPainter {
  final Rect? rect;
  DrawPainter(this.rect,);
  @override
  void paint(Canvas canvas, Size size) {
    // TODO: implement paint
    Paint paint = Paint();
    paint.color = Colors.white;
    paint.style = PaintingStyle.stroke;
    paint.strokeWidth = 5;
    canvas.drawOval(Rect.fromLTWH(rect!.left, rect!.top, rect!.width, rect!.height), paint);
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    // TODO: implement shouldRepaint
    return false;
  }
}

调用：

Positioned(
     child: CustomPaint(
       painter: DrawPainter(Rect.fromLTWH(0, 5, width - 10, height)),
    ),
)