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) {
  var filledPath = ui.Path();
  var borderPath = ui.Path();
  Polygon? lastPolygon;
  int? lastHash;

  // This functions flushes the batched fill and border paths constructed below.
  void drawPaths() {
    if (lastPolygon == null) {
      return;
    }
    final polygon = lastPolygon!;

    // Draw filled polygon .
    if (polygon.isFilled) {
      final paint = Paint()
        ..style = PaintingStyle.fill
        ..color = polygon.color;

      canvas.drawPath(filledPath, paint);
    }

    // Draw polygon outline.
    if (polygon.borderStrokeWidth > 0) {
      final borderPaint = _getBorderPaint(polygon);
      canvas.drawPath(borderPath, borderPaint);
    }

    filledPath = ui.Path();
    borderPath = ui.Path();
    lastPolygon = null;
    lastHash = null;
  }

  // Main loop constructing batched fill and border paths from given polygons.
  for (final polygon in polygons) {
    if (polygon.points.isEmpty) {
      continue;
    }
    final offsets = getOffsets(polygon.points);

    // The hash is based on the polygons visual properties. If the hash from
    // the current and the previous polygon no longer match, we need to flush
    // the batch previous polygons.
    final hash = polygon.renderHashCode;
    if (lastHash != hash) {
      drawPaths();
    }
    lastPolygon = polygon;
    lastHash = hash;

    // First add fills and borders to path.
    if (polygon.isFilled) {
      filledPath.addPolygon(offsets, true);
    }
    if (polygon.borderStrokeWidth > 0.0) {
      _addBorderToPath(borderPath, polygon, offsets);
    }

    // Afterwards deal with more complicated holes.
    final holePointsList = polygon.holePointsList;
    if (holePointsList != null && holePointsList.isNotEmpty) {
      // Ideally we'd use `Path.combine(PathOperation.difference, ...)`
      // instead of evenOdd fill-type, however it creates visual artifacts
      // using the web renderer.
      filledPath.fillType = PathFillType.evenOdd;

      final holeOffsetsList = List<List<Offset>>.generate(
        holePointsList.length,
        (i) => getOffsets(holePointsList[i]),
        growable: false,
      );

      for (final holeOffsets in holeOffsetsList) {
        filledPath.addPolygon(holeOffsets, true);
      }

      if (!polygon.disableHolesBorder && polygon.borderStrokeWidth > 0.0) {
        _addHoleBordersToPath(borderPath, polygon, holeOffsetsList);
      }
    }

    if (!drawLabelsLast && polygonLabels && polygon.textPainter != null) {
      // Labels are expensive because:
      //  * they themselves cannot easily be pulled into our batched path
      //    painting with the given text APIs
      //  * therefore, they require us to flush the batch of polygon draws to
      //    ensure polygons and labels are stacked correctly, i.e.:
      //    p1, p1_label, p2, p2_label, ... .

      // The painter will be null if the layouting algorithm determined that
      // there isn't enough space.
      final painter = buildLabelTextPainter(
        mapSize: map.size,
        placementPoint: map.getOffsetFromOrigin(polygon.labelPosition),
        bounds: getBounds(polygon),
        textPainter: polygon.textPainter!,
        rotationRad: map.rotationRad,
        rotate: polygon.rotateLabel,
        padding: 20,
      );

      if (painter != null) {
        // Flush the batch before painting to preserve stacking.
        drawPaths();

        painter(canvas);
      }
    }
  }

  drawPaths();

  if (polygonLabels && drawLabelsLast) {
    for (final polygon in polygons) {
      if (polygon.points.isEmpty) {
        continue;
      }
      final textPainter = polygon.textPainter;
      if (textPainter != null) {
        final painter = buildLabelTextPainter(
          mapSize: map.size,
          placementPoint: map.getOffsetFromOrigin(polygon.labelPosition),
          bounds: getBounds(polygon),
          textPainter: textPainter,
          rotationRad: map.rotationRad,
          rotate: polygon.rotateLabel,
          padding: 20,
        );

        painter?.call(canvas);
      }
    }
  }
}