void* __stdcall Procedure(void* Window, unsigned Messsage, void* Parameter1, void* Parameter2);
Prototype definition for a window procedure.
The handle of the window.
The message identity.
The first window parameter.
The second window parameter.
The value returned by the window procedure.
Based on its response to individual messages (such as Message::Paint etc), a window procedure defines the operational characteristics of the window. A window procedure is associated with a window class; that is, all windows of a class share the same window procedure. For this reason, if multiple windows of the same class are to be created (within a single process), the window procedure should be reentrant.
A window procedure is defined (to the operating system) through the function RegisterClass. Once registered, the operating system calls the window procedure as required.