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) {
  // DEBUG: Track paint frequency
  if (_debugPaintFrequency) {
    _paintCounter++;
    final now = DateTime.now();
    if (_lastPaintTime != null) {
      final delta = now.difference(_lastPaintTime!).inMilliseconds;
      if (delta < 1000) {
        // Only log if repainting faster than once per second
        debugPrint(
          '[SchematicPainter] paint #$_paintCounter, '
          'delta: ${delta}ms since last paint',
        );
      }
    }
    _lastPaintTime = now;
  }

  // Draw background (matching .node-0 { fill: white } for the canvas area)
  // Fill the viewport background before applying transforms
  canvas.drawRect(Rect.fromLTWH(0, 0, size.width, size.height), _bgPaint);

  // Read current view transform from the notifier (may change between
  // build() calls via the repaint listenable).
  final vt = viewTransform.value;
  _currentScale = vt.scale;
  _currentOffset = vt.offset;

  // Calculate the visible viewport in schematic coordinates for culling
  // This allows us to skip drawing elements that are off-screen
  final viewportRect = Rect.fromLTWH(
    -_currentOffset.dx / _currentScale,
    -_currentOffset.dy / _currentScale,
    size.width / _currentScale,
    size.height / _currentScale,
  );
  _viewportRect = viewportRect;

  // Apply transform
  canvas
    ..save()
    ..translate(_currentOffset.dx, _currentOffset.dy)
    ..scale(_currentScale);

  // Draw nodes (with culling)
  _drawNodes(canvas, viewportRect);

  // Draw expand/collapse indicators above sub-blocks but below edges
  // (hidden during snapshot capture — they are interactive-only UI).
  if (!snapshotMode.value) {
    _drawExpandIndicators(canvas, viewportRect);
  }

  // Draw edges ON TOP of nodes so they're visible (with culling)
  _drawEdges(canvas, viewportRect);

  // Draw ports on top (with culling)
  _drawPorts(canvas, viewportRect);

  canvas.restore();
}