apply method
Implementation
void apply(PdfGraphics canvas) {
final mask = PdfSoftMask(
painter.document,
boundingBox: painter.boundingBox,
);
final maskCanvas = mask.getGraphics();
// maskCanvas.setTransform(canvas.getTransform());
for (final child in children) {
child!.paint(maskCanvas!);
}
canvas.setGraphicState(PdfGraphicState(softMask: mask));
}