I have fixed lots of small bugs this week and set up an old computer with windows XP who support only OpenGL 2.0. At first the app was not recognized by the OS:

not a valid win32 application

Thanks to this article I was able to fix this error quickly, but the second problem introduced with this workaround (using the define _ATL_XP_TARGETING ) is that I have to include the file msvcr100.dll, so to limit the number of DLL file I have chosen to static link the  runtime library with the flag \MT, but I would have to recompile each library I am using with this flag (SFML, Crypto++).

After that, I tried to find a way to implement sprite batching with VBO instead of vertex array but it seem tedious to do that with SFML and not worth the time. VBO are useful to save transfer time between the CPU (client) and the GPU (server) because with vertex array we need to transfer the data each frame. But that’s okay if the program is not highly optimized, it’s probably an overkill for a point and click game. In most cases, vertex arrays are enough but the problem will be in the future: they are deprecated in OpengGL 3.0, and removed in OpenGl 3.1 and above.