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) {
  final paint = Paint()
    ..color = color
    ..strokeWidth = strokeWidth
    ..style = PaintingStyle.stroke
    ..strokeCap = StrokeCap.round;

  final path = Path();

  final startX = source.dx;
  final startY = source.dy;
  final endX = target.dx;
  final endY = target.dy;

  final verticalDistance = (endY - startY).abs();
  final horizontalDistance = (endX - startX).abs();

  final verticalThreshold = 5;

  // Only draw steps if vertical distance is above threshold
  final enableSteps = verticalDistance > verticalThreshold;

  if (!enableSteps) {
    path.moveTo(startX, startY);
    path.lineTo(endX, endY);
  } else {
    final isGoingRight = (endX - startX) >= 0;
    final isGoingDown = (endY - startY) >= 0;

    // Calculate dynamic step sizes based on percentages of distances
    final horizontalStep =
        horizontalDistance * horizontalStepPercent * (isGoingRight ? 1 : -1);
    final verticalStep =
        verticalDistance * verticalStepPercent * (isGoingDown ? 1 : -1);

    // Clamp corner radius to reasonable range (e.g. no more than min(horizontalStep, verticalStep))
    final maxCorner = [
      horizontalStep.abs(),
      verticalStep.abs(),
    ].reduce((a, b) => a < b ? a : b);
    final corner = cornerRadius.clamp(0.0, maxCorner);

    path.moveTo(startX, startY);

    // Horizontal segment before corner
    path.lineTo(
      startX + horizontalStep - corner * (isGoingRight ? 1 : -1),
      startY,
    );

    // Quadratic bezier corner (horizontal to vertical)
    path.quadraticBezierTo(
      startX + horizontalStep,
      startY,
      startX + horizontalStep,
      startY + verticalStep * 0.5,
    );

    // Vertical segment
    path.lineTo(startX + horizontalStep, endY - verticalStep * 0.5);

    // Quadratic bezier corner (vertical to horizontal)
    path.quadraticBezierTo(
      startX + horizontalStep,
      endY,
      startX + horizontalStep + corner * (isGoingRight ? 1 : -1),
      endY,
    );

    // Final horizontal segment to target
    path.lineTo(endX, endY);
  }

  if (isDashed) {
    _drawDashedPath(canvas, path, paint);
  } else {
    canvas.drawPath(path, paint);
  }
}