sc_vtb_copy
sc_vtb_copy(scp->history, pos,
sc_vtb_copy(&scp->vtb, from, &scp->scr, from, count);
sc_vtb_copy(&scp->scr, 0, &scp->vtb, 0, scp->xsize*scp->ysize);
sc_vtb_copy(&old, 0, &new, 0, scp->xsize*scp->ysize);
void sc_vtb_copy(sc_vtb_t *vtb1, int from, sc_vtb_t *vtb2, int to,