> Yes, you have to lock it if you use it in a thread.
your threads are executed. So your main thread should be blocked during your operation (for example using WaitForMultipleObjects). But it's no problem to have any number of threads working on one or more bitmaps without locking, if you are only accessing the memory given by the scanline property.
-- Jens Gruschel http://www.pegtop.net