Function switch_terrain

src/hack.c:3177–3217

moving onto different terrain; might be going into solid rock, inhibiting levitation or flight, or coming back out of such, reinstating levitation/flying */

   might be going into solid rock, inhibiting levitation or flight,
   or coming back out of such, reinstating levitation/flying */
void
switch_terrain(void)
{
    struct rm *lev = &levl[u.ux][u.uy];
    boolean blocklev = (IS_OBSTRUCTED(lev->typ) || closed_door(u.ux, u.uy)
                        || IS_WATERWALL(lev->typ)
                        || lev->typ == LAVAWALL),
            was_levitating = !!Levitation, was_flying = !!Flying;

    if (blocklev) {
        /* called from spoteffects(), stop levitating but skip float_down() */
        if (Levitation)
            You_cant("levitate in here.");
        BLevitation |= FROMOUTSIDE;
    } else if (BLevitation) {
        BLevitation &= ~FROMOUTSIDE;
        /* we're probably levitating now; if not, we must be chained
           to a buried iron ball so get float_up() feedback for that */
        if (Levitation || BLevitation)
            float_up();
    }
    /* the same terrain that blocks levitation also blocks flight */
    if (blocklev) {
        if (Flying)
            You_cant("fly in here.");
        BFlying |= FROMOUTSIDE;
    } else if (BFlying) {
        BFlying &= ~FROMOUTSIDE;
        float_vs_flight(); /* maybe toggle (BFlying & I_SPECIAL) */
        /* [minor bug: we don't know whether this is beginning flight or
           resuming it; that could be tracked so that this message could
           be adjusted to "resume flying", but isn't worth the effort...] */
        if (Flying)
            You("start flying.");
    }
    if ((!!Levitation ^ was_levitating) || (!!Flying ^ was_flying))
        disp.botl = TRUE; /* update Lev/Fly status condition */

    if (flags.terrainstatus)
        classify_terrain();
}

/* set or clear u.uinwater */
void