Win32 WM_SETCURSOR，WM_MOUSEMOVE总是成对？

I'm working on a Win32 control. There could be hundreds of "items" on this control. Those are not windows, but internal objects (eg: rectangles). Depending on the mouse position I want to change the mouse cursor. That is fine, I can use WM_SETCURSOR.I'm working on a Win32 control. There could be