paint method

@override void paint(Canvas canvas, Size size)

Called whenever the object needs to paint. The given Canvas has its coordinate space configured such that the origin is at the top left of the box. The area of the box is the size of the size argument.

Paint operations should remain inside the given area. Graphical operations outside the bounds may be silently ignored, clipped, or not clipped. It may sometimes be difficult to guarantee that a certain operation is inside the bounds (e.g., drawing a rectangle whose size is determined by user inputs). In that case, consider calling Canvas.clipRect at the beginning of paint so everything that follows will be guaranteed to only draw within the clipped area.

Implementations should be wary of correctly pairing any calls to Canvas.save/Canvas.saveLayer and Canvas.restore, otherwise all subsequent painting on this canvas may be affected, with potentially hilarious but confusing results.

To paint text on a Canvas, use a TextPainter.

To paint an image on a Canvas:

1. Obtain an ImageStream, for example by calling ImageProvider.resolve on an AssetImage or NetworkImage object.

2. Whenever the ImageStream's underlying ImageInfo object changes (see ImageStream.addListener), create a new instance of your custom paint delegate, giving it the new ImageInfo object.

3. In your delegate's paint method, call the Canvas.drawImage, Canvas.drawImageRect, or Canvas.drawImageNine methods to paint the ImageInfo.image object, applying the ImageInfo.scale value to obtain the correct rendering size.

Implementation

@override
void paint(Canvas canvas, Size size) {
  if (data.isEmpty) return;

  // Calculate the maximum radius that will fit in the canvas
  // considering we need space for the amplitude bars
  if (radius == -1) {
    double minDimension = size.height < size.width ? size.height : size.width;
    // Use 1/3 of the minimum dimension for the base circle radius
    // This leaves room for the amplitude bars to stay within bounds
    radius = minDimension / 6;
    double circumference = 2 * pi * radius;
    wavePaint.strokeWidth = circumference / (data.length * 2);
    wavePaint.style = PaintingStyle.stroke;
  }

  // Center point
  final center = Offset(size.width / 2, size.height / 2);

  // Draw base circle
  canvas.drawCircle(
    center,
    radius.toDouble(),
    wavePaint,
  );

  if (points == null || points!.length < data.length * 4) {
    points = Float32List(data.length * 4);
  }

  // Find the maximum value in the data for scaling
  double maxValue = data.reduce((curr, next) => curr > next ? curr : next);
  if (maxValue == 0) maxValue = 1; // Prevent division by zero

  double angle = 0;
  double angleIncrement = 360 / data.length;

  // Calculate maximum safe amplitude that won't exceed canvas bounds
  // This ensures bars won't extend beyond the smaller dimension of the canvas
  double maxAmplitude = min(
      (size.width / 2 - radius) * 0.8, // 80% of available width space
      (size.height / 2 - radius) * 0.8 // 80% of available height space
      );

  for (int i = 0; i < data.length; i++) {
    // Scale the value relative to the maximum value and the safe amplitude
    double normalizedValue = data[i] / maxValue;
    double barHeight = normalizedValue * maxAmplitude;

    // Calculate points for this bar
    double angleRad = angle * pi / 180.0;
    double cosAngle = cos(angleRad);
    double sinAngle = sin(angleRad);

    // Start point (on the base circle)
    points![i * 4] = center.dx + radius * cosAngle;
    points![i * 4 + 1] = center.dy + radius * sinAngle;

    // End point (extended by bar height)
    points![i * 4 + 2] = center.dx + (radius + barHeight) * cosAngle;
    points![i * 4 + 3] = center.dy + (radius + barHeight) * sinAngle;

    angle += angleIncrement;
  }

  canvas.drawRawPoints(PointMode.lines, points!, wavePaint);
}