prePaintDragHandle method
Prepares the canvas with the current drag handle offset.
Must be called at the start of paint().
Implementation
@protected
@mustCallSuper
void prePaintDragHandle(Canvas canvas, Size size, Denormalize denormalize) {
canvas.save();
final dragHandle = denormalize(_dragHandleOffset);
canvas.translate(dragHandle.dx, dragHandle.dy);
}