createImageFromWidget function

Future<Uint8List> createImageFromWidget(Widget widget, { Size? logicalSize, required Duration waitToRender, required FlutterView view, Size? imageSize, })

Creates a PNG image from the given widget by spinning up an element and render tree.

The final image will be of size imageSize and the widget will be laid out with the given logicalSize. By default both are calculated from view.

Inlined from package:widget_to_marker to avoid depending on google_maps_flutter.

Implementation

Future<Uint8List> createImageFromWidget(
  Widget widget, {
  Size? logicalSize,
  required Duration waitToRender,
  required ui.FlutterView view,
  Size? imageSize,
}) async {
  final RenderRepaintBoundary repaintBoundary = RenderRepaintBoundary();
  logicalSize ??= view.physicalSize / view.devicePixelRatio;
  imageSize ??= view.physicalSize;

  final RenderView renderView = RenderView(
    view: view,
    child: RenderPositionedBox(
        alignment: Alignment.center, child: repaintBoundary),
    configuration: ViewConfiguration(
      physicalConstraints:
          BoxConstraints.tight(logicalSize) * view.devicePixelRatio,
      logicalConstraints: BoxConstraints.tight(logicalSize),
      devicePixelRatio: view.devicePixelRatio,
    ),
  );

  final PipelineOwner pipelineOwner = PipelineOwner();
  final BuildOwner buildOwner = BuildOwner(focusManager: FocusManager());

  pipelineOwner.rootNode = renderView;
  renderView.prepareInitialFrame();

  final RenderObjectToWidgetElement<RenderBox> rootElement =
      RenderObjectToWidgetAdapter<RenderBox>(
    container: repaintBoundary,
    child: widget,
  ).attachToRenderTree(buildOwner);

  buildOwner.buildScope(rootElement);

  await Future.delayed(waitToRender);

  buildOwner.buildScope(rootElement);
  buildOwner.finalizeTree();

  pipelineOwner.flushLayout();
  pipelineOwner.flushCompositingBits();
  pipelineOwner.flushPaint();

  final ui.Image image = await repaintBoundary.toImage(
      pixelRatio: imageSize.width / logicalSize.width);
  final ByteData? byteData =
      await image.toByteData(format: ui.ImageByteFormat.png);

  return byteData!.buffer.asUint8List();
}