flutter_triangle_painter.dart

class CustomTrianglePainter extends CustomPainter {
  final Color color;
  late Paint _paint;

  CustomTrianglePainter(this.color) {
    _paint = Paint()
      ..color = color
      ..style = PaintingStyle.fill;
  }

  @override
  void paint(Canvas canvas, Size size) {
    var path = Path();
    path.moveTo(size.width / 2, 0);
    path.lineTo(0, size.height);
    path.lineTo(size.width, size.height);
    path.close();
    canvas.drawPath(path, _paint);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    return false;
  }
}