At the heart of Windows 95 and Windows NT is a messaging system that is the basis for most of what goes on in their respective systems. Messages are the "atomic" events that programmers can respond to. For example, whenever you press a key there can be up to 3 messages generated: WM_KEYDOWN, WM_KEYUP and WM_CHAR. Other releated messages are generated for systems keys (the alt key). These messages are passed to the appropriate window for handling. There are several ways to generate messages. Windows can create them in response to hardware events such as keystrokes or mouse clicks or software events such as when a screen needs repainting. Programmers can create them to send information or notifications to themselves or others. In general, the way in which programmers respond to these message events determines how a program runs. If you want to change the behavior of a particular window, you need to respond to the appropriate message and act accordingly. The behavior of windows are controlled by a thing called a Window Procedure or WindProc. Essentially, a WindProc is a function that acts as a filter. As messages are generated and passed to a window for possible handling, the WindProc is where a programmer looks at this stream of messages and picks the ones he is interested in processing. If the message is of no interest it is passed back to Windows for default processing. In many programming environments access to this message stream is limited or impossible. Using the Message Blaster , you can respond to just about any message in any window.
