paintPathStroke static method

void paintPathStroke(Canvas canvas, Path path, Color color, { required double strokeWidth, double strokeAlign = 0.0, StrokeCap strokeCap = .butt, StrokeJoin strokeJoin = .miter, double strokeMiterLimit = 4.0, })

Implementation

static void paintPathStroke(
  Canvas canvas,
  Path path,
  Color color, {
  required double strokeWidth,
  double strokeAlign = 0.0,
  StrokeCap strokeCap = .butt,
  StrokeJoin strokeJoin = .miter,
  double strokeMiterLimit = 4.0,
}) {
  // Early return if the stroke would be invisible.
  if (strokeWidth == 0.0 || color.a <= 0.0) return;

  // Explicitly set miter limit to 0 if not using miter.
  if (strokeJoin != .miter) strokeMiterLimit = 0.0;

  final paint = Paint()
    ..style = .stroke
    ..color = color
    ..strokeCap = strokeCap
    ..strokeJoin = strokeJoin
    ..strokeMiterLimit = strokeMiterLimit;

  // The most optimal path is when the stroke is center-aligned.
  // BorderSide.strokeAlignCenter is explicitly not used here.
  if (strokeAlign == 0.0) {
    paint.strokeWidth = strokeWidth;
    canvas.drawPath(path, paint);
    return;
  }

  // Inlined from [BorderSide].
  final strokeInset = strokeWidth * (1.0 - (1.0 + strokeAlign) / 2.0);
  final strokeOutset = strokeWidth * (1.0 + strokeAlign) / 2.0;

  final minOffset = math.min(strokeInset, strokeOutset);
  final maxOffset = math.max(strokeInset, strokeOutset);

  // Compute the minimum safe bounds for the layer and clip path.
  final maxMiterLength = math.max(maxOffset, maxOffset * strokeMiterLimit);
  final bounds = path.getBounds().inflate(maxMiterLength);

  // Save layer is needed for compound strokes with a translucent color.
  final needsSaveLayer =
      color.a < 1.0 && strokeInset > 0.0 && strokeOutset > 0.0;

  // Apply opacity to everything.
  if (needsSaveLayer) {
    canvas.saveLayer(
      bounds,
      Paint()..color = color.withValues(red: 0.0, green: 0.0, blue: 0.0),
    );
    paint.color = color.withValues(alpha: 1.0);
  }

  // Paint the lesser offset.
  if (minOffset > 0.0) {
    paint.strokeWidth = 2.0 * minOffset;
    canvas.drawPath(path, paint);
  }

  // Paint the greater offset.
  paint.strokeWidth = 2.0 * maxOffset;
  if (strokeInset > strokeOutset) {
    // Clip the inside of the path.
    canvas
      ..save()
      ..clipPath(path)
      ..drawPath(path, paint)
      ..restore();
  } else {
    // Clip the outside of the path.
    canvas
      ..save()
      ..clipPath(.combine(.difference, Path()..addRect(bounds), path))
      ..drawPath(path, paint)
      ..restore();
  }

  // Don't forget to restore the canvas if needed.
  if (needsSaveLayer) {
    canvas.restore();
  }
}