Displaying tooltips during mousedrag

I'd like to display a tooltip while a user is dragging a mouse to create a rectangle. The contents of the tooltip would be an indication of the size of the rectangle. I don't know how to get the tooltip to display when the mouse button is down, and to stop displaying when the mouse button is up.

The application is written in C++ on Windows, using Visual Studio 2开发者_运维百科005, no MFC, no ATL.

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Try sending a TTM_ACTIVATE message to turn the tooltip window on or off.