Generally, in
GUI programming, callback is a function that handles some
event. For example:
glutMouseFunc(mouse);
With this command, GLUT program will then use function mouse as callback to handle mouse clicks. Example:
void mouse(int button, int state, int x, int y)
{
switch(button) {
case GLUT_LEFT_BUTTON:
if(state==GLUT_DOWN)
clicked(x,y);
break;
case GLUT_MIDDLE_BUTTON:
if(state==GLUT_DOWN)
reset_state();
break;
}
}
This callback will receive mouse button state and click coordinates through the function parameters.
Callbacks aren't always called callbacks, but the idea is same often in GUI programming. =)