shouldRepaint method Null safety

Called whenever a new instance of the raster widget delegate class is provided to the RenderRasterWidget object, or any time that a new RasterWidgetDelegate object is created with a new instance of the delegate class (which amounts to the same thing, because the latter is implemented in terms of the former).

If the new instance represents different information than the old instance, then the method should return true, otherwise it should return false.

If the method returns false, then the paint call might be optimized away.

It's possible that the paint method will get called even if shouldRepaint returns false (e.g. if an ancestor or descendant needed to be repainted). It's also possible that the paint method will get called without shouldRepaint being called at all (e.g. if the box changes size).

Changing the delegate will not cause the child image retained by the RenderRasterWidget to be updated. Instead, RasterWidgetController.clear can be used to force the generation of a new image.

The oldDelegate argument will never be null.