ShaderMask({Key key, @required ShaderCallback shaderCallback, TransferMode transferMode: TransferMode.modulate, Widget child })

Creates a widget that applies a mask generated by a Shader to its child.

The shaderCallback and transferMode arguments must not be null.

Source 

ShaderMask({
  Key key,
  @required this.shaderCallback,
  this.transferMode: TransferMode.modulate,
  Widget child
}) : super(key: key, child: child) {
  assert(shaderCallback != null);
  assert(transferMode != null);
}