Problem exists in Livewire, Paintbrush and erase tool.
the feedback contour: in Liverwire the green thingy, paint /erase red lines before action is finished)
every time SetData() is called on a DataNode,
a new mapper is generated (costly!),
when updating the feedback contour, in the three cases above,
instead of updating the actual data, new feedback objects are genarated and then assigned the DataNode using ->SetData().
this has the effect that every tiny mouse movement a mapper is destroyed and a new one is again created.
solution:
instead of creating a new contour object and replacing the old one,
the actual contour should be modified, this way the mapper can stay the same,
thus speeding up rendering.