drawText method

void drawText(Canvas canvas, Offset position, TextStyle style, int angle,)

Draws the context (label) of a plotband.

Allows a complete customization of bespoke typography, dynamic positioning, drop shadows, or interactive effects.

position represents the top-left origin of the text. angle is the clockwise rotation angle in degrees.

Example – render a rotated label with a pill-shaped highlight:

class RibbonLabelPlotBand extends PlotBand {
  const RibbonLabelPlotBand()
      : super(text: 'Target Range', textAngle: 45);

  @override
  void drawText(Canvas canvas, Offset position, TextStyle style,
    int angle) {
    final TextPainter painter = TextPainter(
      text: TextSpan(text: text),
      textAlign: TextAlign.center,
      textDirection: TextDirection.ltr,
    )..layout();
    final Offset center =
        position + Offset(painter.width / 2, painter.height / 2);

    canvas.save();
    canvas.translate(center.dx, center.dy);
    canvas.rotate(angle * (pi / 180));
    final Rect capsule = Rect.fromCenter(
      center: Offset.zero,
      width: painter.width + 12,
      height: painter.height + 8,
    );
    canvas.drawRRect(
      RRect.fromRectAndRadius(capsule, const Radius.circular(12)),
      Paint()..color = Colors.deepPurple.withAlpha(115),
    );
    painter.paint(canvas,
      Offset(-painter.width / 2, -painter.height / 2));
    canvas.restore();
  }
}

Implementation

void drawText(Canvas canvas, Offset position, TextStyle style, int angle) {
  if (text == null || text!.isEmpty) {
    return;
  }
  final TextSpan span = TextSpan(text: text, style: style);
  final TextPainter textPainter = TextPainter(
    text: span,
    textAlign: TextAlign.center,
    textDirection: TextDirection.ltr,
  );
  textPainter.layout();
  if (angle == 0) {
    textPainter.paint(canvas, position);
  } else {
    final double halfWidth = textPainter.width / 2;
    final double halfHeight = textPainter.height / 2;
    canvas
      ..save()
      ..translate(position.dx + halfWidth, position.dy + halfHeight)
      ..rotate(degreesToRadians(angle.toDouble()));
    textPainter.paint(canvas, Offset(-halfWidth, -halfHeight));
    canvas.restore();
  }
}