The Callback function must be declared as a global function (commonly used in C language), or the class of Static member functions (OO). In order to avoid the impact of this pointer. It's not very clear to use it. Some Windows APIs require a pointer to the Callback function as an incoming parameter. BOOL LineDDA (int nXStart, // x-coordinate of line's starting point int nYStart, // y-coordinate of line's starting point int nXEnd, // x-coordinate of line's ending point int nYEnd, // y-coordinate of line's ending Point Lineddaproc LPLINEFUNC, / / POINTER TO CALLBACK FUNTER TO Application-Defined Data; Now I know this situation, I hope that I can really understand what is going on.
