for i=0 to n-1 do { 
           drawframe(i);
        }

        global i = 0;

        function drawframeCB() {
            if (i < n)
                drawframe(i);
            i = i + 1;
        }

        int i = 0;
        registerCB(drawframeCB, &i)

        function drawframeCB(int *pi) {
            i = *pi;
            if (i < n)
                drawframe(i);
            *pi = i + 1;
        }

        registerCB(drawframeCB)

        function drawframeCB(float t) {
            i = int(t / 30)
            drawframe(i);
        }

• In one process
• In multiple process program