captureBoundaryToPng function

Future<bool> captureBoundaryToPng(
  1. BuildContext context, {
  2. required GlobalKey<State<StatefulWidget>> boundaryKey,
  3. String filePrefix = 'export',
  4. double pixelRatio = 2.0,
  5. Future<String?> saveFn(
    1. Uint8List pngBytes,
    2. String fileName
    )?,
  6. Future<Uint8List?> encodeFn(
    1. RenderRepaintBoundary boundary,
    2. double pixelRatio
    )?,
})

Capture a RepaintBoundary identified by boundaryKey, encode to PNG, save/download, and show a toast.

filePrefix is used as the first part of the file name (e.g. "schematic" → schematic_1713052800000.png).

When saveFn is provided it is used instead of the default platform save/download. This allows callers (e.g. VS Code webview hosts) to route the PNG bytes through a native Save dialog. saveFn receives the raw PNG bytes and a suggested file name, and should return the saved path (or null if no path feedback is available).

pixelRatio controls the output resolution multiplier. Defaults to 2.0 which works well in webview-constrained environments and keeps PNG sizes manageable for postMessage serialisation. Callers that need print-quality output (e.g. schematic exports) should pass a higher value explicitly.

Returns true if the export succeeded.

Implementation

Future<bool> captureBoundaryToPng(
  BuildContext context, {
  required GlobalKey boundaryKey,
  String filePrefix = 'export',
  double pixelRatio = 2.0,
  Future<String?> Function(Uint8List pngBytes, String fileName)? saveFn,
  Future<Uint8List?> Function(
    RenderRepaintBoundary boundary,
    double pixelRatio,
  )? encodeFn,
}) async {
  final renderObject = boundaryKey.currentContext?.findRenderObject();
  if (renderObject is! RenderRepaintBoundary) {
    debugPrint('[ExportPng] No RepaintBoundary found');
    return false;
  }
  final boundary = renderObject;

  final encode = encodeFn ?? _encodeBoundaryToPng;
  final pngBytes = await encode(boundary, pixelRatio);

  if (pngBytes == null) {
    debugPrint('[ExportPng] Failed to encode PNG');
    return false;
  }

  final fileName = '${filePrefix}_${DateTime.now().millisecondsSinceEpoch}.png';

  try {
    final save = saveFn ?? export_png.savePngBytes;
    final savedPath = await save(pngBytes, fileName);
    final msg =
        savedPath != null ? 'Saved: $savedPath' : 'Downloaded $fileName';
    debugPrint('[ExportPng] $msg');
    if (context.mounted) {
      export_png.showExportToast(context, msg);
    }
    return true;
  } on Object catch (e) {
    debugPrint('[ExportPng] Export failed: $e');
    if (context.mounted) {
      export_png.showExportToast(context, 'Export failed: $e');
    }
    return false;
  }
}