paint method

  1. @override
void paint(
  1. Canvas canvas,
  2. Size size
)
override

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 gridSize = spatialIndex.gridSize;
  if (gridSize <= 0) return;

  // Calculate visible area in world coordinates
  final zoom = viewport.zoom;
  final viewportLeft = -viewport.x / zoom;
  final viewportTop = -viewport.y / zoom;
  final viewportRight = viewportLeft + (size.width / zoom);
  final viewportBottom = viewportTop + (size.height / zoom);

  // Calculate which grid cells are potentially visible
  // Add padding to ensure we draw cells that are partially visible
  final startCellX = (viewportLeft / gridSize).floor() - 1;
  final endCellX = (viewportRight / gridSize).ceil() + 1;
  final startCellY = (viewportTop / gridSize).floor() - 1;
  final endCellY = (viewportBottom / gridSize).ceil() + 1;

  // Get active cells info for highlighting cells with objects
  final activeCells = spatialIndex.getActiveCellsInfo();
  final activeCellMap = <String, CellDebugInfo>{};
  for (final cell in activeCells) {
    activeCellMap['${cell.cellX}_${cell.cellY}'] = cell;
  }

  // Calculate which cell the mouse is in (if mouse position is available)
  int? mouseCellX;
  int? mouseCellY;
  if (mousePositionWorld != null) {
    mouseCellX = (mousePositionWorld!.dx / gridSize).floor();
    mouseCellY = (mousePositionWorld!.dy / gridSize).floor();
  }

  const borderWidth = 0.5;

  // Paint for grid lines (inactive cells use reddish border)
  final gridPaint = Paint()
    ..color = theme.borderColor
    ..strokeWidth =
        borderWidth /
        zoom // Scale with zoom
    ..style = PaintingStyle.stroke;

  // Paint for active cell fill (greenish)
  final activeFillPaint = Paint()
    ..color = theme.activeColor
    ..style = PaintingStyle.fill;

  // Paint for active cell border (greenish, same thickness)
  final activeBorderPaint = Paint()
    ..color = theme.activeBorderColor
    ..strokeWidth = borderWidth / zoom
    ..style = PaintingStyle.stroke;

  // Pass 1: Draw all inactive cell borders (baseline grid)
  for (int cellX = startCellX; cellX <= endCellX; cellX++) {
    for (int cellY = startCellY; cellY <= endCellY; cellY++) {
      final bounds = spatialIndex.cellBounds(cellX, cellY);
      final cellKey = '${cellX}_$cellY';
      final isActive = activeCellMap.containsKey(cellKey);

      // Only draw inactive cell borders in this pass
      if (!isActive) {
        canvas.drawRect(bounds, gridPaint);
      }
    }
  }

  // Pass 2: Draw active cells (fill + border) on top
  // This ensures active cell borders are fully visible
  for (int cellX = startCellX; cellX <= endCellX; cellX++) {
    for (int cellY = startCellY; cellY <= endCellY; cellY++) {
      final bounds = spatialIndex.cellBounds(cellX, cellY);
      final cellKey = '${cellX}_$cellY';
      final cellInfo = activeCellMap[cellKey];
      final isActive = cellInfo != null;

      if (isActive) {
        // Draw fill first, then border on top
        canvas.drawRect(bounds, activeFillPaint);
        canvas.drawRect(bounds, activeBorderPaint);
      }
    }
  }

  // Pass 3: Draw labels on top of grid cells
  for (int cellX = startCellX; cellX <= endCellX; cellX++) {
    for (int cellY = startCellY; cellY <= endCellY; cellY++) {
      final bounds = spatialIndex.cellBounds(cellX, cellY);
      final cellKey = '${cellX}_$cellY';
      final cellInfo = activeCellMap[cellKey];
      final isMouseCell = cellX == mouseCellX && cellY == mouseCellY;

      _drawCellLabel(
        canvas,
        bounds,
        cellX,
        cellY,
        cellInfo,
        isMouseCell,
        zoom,
      );
    }
  }

  // Pass 4-6: Draw element bounds in order: connections → nodes → ports
  _drawConnectionSegments(canvas, zoom);
  _drawNodeBounds(canvas, zoom);
  _drawPortSnapZones(canvas, zoom);
}