Clip Container inside CustomPainter

Question

i made this shape using CustumPainter Class , i want the container color to fill only the shape , like a full charged battery

this is how i made the shape

void paint(Canvas canvas, Size size) {
    var paint = Paint();

    var path = Path();
    paint.color = Colors.black;
    paint.style = PaintingStyle.stroke;
    paint.strokeWidth = 4.0;
    var posX;
    var posY;
    
    path.lineTo(size.width*0.75, 0);


    path.lineTo(size.width*0.75, size.height*0.25);

    path.lineTo(size.width*0.75, size.height);
    path.lineTo(0, size.height);
    path.lineTo(0, 0);
    path.moveTo(size.width*0.75, size.height*0.25);
    path.lineTo(size.width*0.80, size.height*0.25);
    path.lineTo(size.width*0.80, size.height*0.75);
    path.lineTo(size.width*0.75, size.height*0.75);



    canvas.drawPath(path, paint);
  }

and this is my widget

return ClipRRect(
      child: Container(
        width: 100,
        color: Colors.red,
        height: 50,
        child: CustomPaint(
          child: Container(
          ),
          painter: BatteryPainter(),
        ),
      ),
    );

Answer 1

Create another Path/rect inside Painter to handle fill color property , Also include Paint()..strokeCap = StrokeCap.round for better look on outer side.

, pass the value to control fill color.

class BatteryPainter extends CustomPainter {
  final Color fillColor;
  final double value;
  BatteryPainter({
    required this.value,
    this.fillColor = Colors.red,
  });

  @override
  void paint(Canvas canvas, Size size) {
    var paint = Paint()..strokeCap = StrokeCap.round;

    var path = Path();
    paint.color = Colors.black;
    paint.style = PaintingStyle.stroke;
    paint.strokeWidth = 4.0;

    path.lineTo(size.width * 0.75, 0);

    path.lineTo(size.width * 0.75, size.height * 0.25);

    path.lineTo(size.width * 0.75, size.height);
    path.lineTo(0, size.height);
    path.lineTo(0, 0);
    path.moveTo(size.width * 0.75, size.height * 0.25);
    path.lineTo(size.width * 0.80, size.height * 0.25);
    path.lineTo(size.width * 0.80, size.height * 0.75);
    path.lineTo(size.width * 0.75, size.height * 0.75);

    Rect rect = Rect.fromLTWH(0, 0, size.width * 0.75 * value, size.height);
    canvas.drawPath(path, paint);

    canvas.drawRect(
        rect,
        Paint()
          ..color = fillColor
          ..style = PaintingStyle.fill);
  }

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

Use

Container(
  width: 100,
  height: 50,
  child: CustomPaint(
    painter: BatteryPainter(value: value),
  ),
),