How do I draw a vector shape in Flutter?

Question

We are trying to build a custom shape vector in Flutter that can be changed at runtime.

For example, we need a pizza shape vector widget that we can change the slice color base on a variable value.

We tried to use the canvas and painter in Flutter but they don't have a clear and good doc.

We tried SVG too but unfortunately Flutter doesn't support SVG tag and SVG view too.

Solution

You can create a widget that extends CustomPainter

class Sky extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    var rect = Offset.zero & size;
    var gradient = new RadialGradient(
      center: const Alignment(0.7, -0.6),
      radius: 0.2,
      colors: [const Color(0xFFFFFF00), const Color(0xFF0099FF)],
      stops: [0.4, 1.0],
    );
    canvas.drawRect(
      rect,
      new Paint()..shader = gradient.createShader(rect),
    );
  }

  @override
  SemanticsBuilderCallback get semanticsBuilder {
    return (Size size) {
      // Annotate a rectangle containing the picture of the sun
      // with the label "Sun". When text to speech feature is enabled on the
      // device, a user will be able to locate the sun on this picture by
      // touch.
      var rect = Offset.zero & size;
      var width = size.shortestSide * 0.4;
      rect = const Alignment(0.8, -0.9).inscribe(new Size(width, width), rect);
      return [
        new CustomPainterSemantics(
          rect: rect,
          properties: new SemanticsProperties(
            label: 'Sun',
            textDirection: TextDirection.ltr,
          ),
        ),
      ];
    };
  }

  // Since this Sky painter has no fields, it always paints
  // the same thing and semantics information is the same.
  // Therefore we return false here. If we had fields (set
  // from the constructor) then we would return true if any
  // of them differed from the same fields on the oldDelegate.
  @override
  bool shouldRepaint(Sky oldDelegate) => false;
  @override
  bool shouldRebuildSemantics(Sky oldDelegate) => false;
}

See also

• https://pub.dartlang.org/packages/flutter_svg (limited SVG support for Flutter)
• https://github.com/flutter/flutter/tree/master/dev/tools/vitool
• https://github.com/simolus3/fluttie (not sure this is working already)