BeginRectTracking
void BeginRectTracking(BRect r, bool trackWhole);
void BeginRectTracking(BRect startRect,
BView::BeginRectTracking(BRect(origin, origin), B_TRACK_RECT_CORNER);
fCanvasView->BeginRectTracking(BRect(where, where),
BeginRectTracking(dragRect, B_TRACK_WHOLE_RECT);
BeginRectTracking(dragRect, B_TRACK_WHOLE_RECT);
fTitleView->BeginRectTracking(rect);