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) {
  const distance = Distance();
  final rect = Offset.zero & size;
  canvas.clipRect(rect);

  // Let's calculate all the points grouped by color and radius
  final points = <Color, Map<double, List<Offset>>>{};
  final pointsFilledBorder = <Color, Map<double, List<Offset>>>{};
  final pointsBorder = <Color, Map<double, Map<double, List<Offset>>>>{};
  for (final circle in circles) {
    final offset = map.getOffsetFromOrigin(circle.point);
    double radius = circle.radius;
    if (circle.useRadiusInMeter) {
      final r = distance.offset(circle.point, circle.radius, 180);
      final delta = offset - map.getOffsetFromOrigin(r);
      radius = delta.distance;
    }
    points[circle.color] ??= {};
    points[circle.color]![radius] ??= [];
    points[circle.color]![radius]!.add(offset);

    if (circle.borderStrokeWidth > 0) {
      // Check if color have some transparency or not
      // As drawPoints is more efficient than drawCircle
      if (circle.color.alpha == 0xFF) {
        double radiusBorder = circle.radius + circle.borderStrokeWidth;
        if (circle.useRadiusInMeter) {
          final rBorder = distance.offset(circle.point, radiusBorder, 180);
          final deltaBorder = offset - map.getOffsetFromOrigin(rBorder);
          radiusBorder = deltaBorder.distance;
        }
        pointsFilledBorder[circle.borderColor] ??= {};
        pointsFilledBorder[circle.borderColor]![radiusBorder] ??= [];
        pointsFilledBorder[circle.borderColor]![radiusBorder]!.add(offset);
      } else {
        double realRadius = circle.radius;
        if (circle.useRadiusInMeter) {
          final rBorder = distance.offset(circle.point, realRadius, 180);
          final deltaBorder = offset - map.getOffsetFromOrigin(rBorder);
          realRadius = deltaBorder.distance;
        }
        pointsBorder[circle.borderColor] ??= {};
        pointsBorder[circle.borderColor]![circle.borderStrokeWidth] ??= {};
        pointsBorder[circle.borderColor]![circle.borderStrokeWidth]![
            realRadius] ??= [];
        pointsBorder[circle.borderColor]![circle.borderStrokeWidth]![
                realRadius]!
            .add(offset);
      }
    }
  }

  // Now that all the points are grouped, let's draw them
  final paintBorder = Paint()..style = PaintingStyle.stroke;
  for (final color in pointsBorder.keys) {
    final paint = paintBorder..color = color;
    for (final borderWidth in pointsBorder[color]!.keys) {
      final pointsByRadius = pointsBorder[color]![borderWidth]!;
      final radiusPaint = paint..strokeWidth = borderWidth;
      for (final radius in pointsByRadius.keys) {
        final pointsByRadiusColor = pointsByRadius[radius]!;
        for (final offset in pointsByRadiusColor) {
          _paintCircle(canvas, offset, radius, radiusPaint);
        }
      }
    }
  }

  // Then the filled border in order to be under the circle
  final paintPoint = Paint()
    ..isAntiAlias = false
    ..strokeCap = StrokeCap.round;
  for (final color in pointsFilledBorder.keys) {
    final paint = paintPoint..color = color;
    final pointsByRadius = pointsFilledBorder[color]!;
    for (final radius in pointsByRadius.keys) {
      final pointsByRadiusColor = pointsByRadius[radius]!;
      final radiusPaint = paint..strokeWidth = radius * 2;
      _paintPoints(canvas, pointsByRadiusColor, radiusPaint);
    }
  }

  // And then the circle
  for (final color in points.keys) {
    final paint = paintPoint..color = color;
    final pointsByRadius = points[color]!;
    for (final radius in pointsByRadius.keys) {
      final pointsByRadiusColor = pointsByRadius[radius]!;
      final radiusPaint = paint..strokeWidth = radius * 2;
      _paintPoints(canvas, pointsByRadiusColor, radiusPaint);
    }
  }
}