mouse_callback - Man Page

#include <allegro.h>

extern void (*mouse_callback)(int flags);

Called by the interrupt handler whenever the mouse moves or one of the  buttons changes state. This function must be in locked memory, and must  execute _very_ quickly! It is passed the event flags that triggered the  call, which is a bitmask containing any of the values MOUSE_FLAG_MOVE,  MOUSE_FLAG_LEFT_DOWN, MOUSE_FLAG_LEFT_UP, MOUSE_FLAG_RIGHT_DOWN,  MOUSE_FLAG_RIGHT_UP, MOUSE_FLAG_MIDDLE_DOWN, MOUSE_FLAG_MIDDLE_UP, and  MOUSE_FLAG_MOVE_Z. Note that even if the mouse has more than three buttons, only the first three can be trapped using a callback.

install_mouse(3)