workaround a bug in cursor positioning

this testprogram is supposed to create a rotating wheel animation:

  #include <ncurses.h>
  #include <unistd.h>

  int main() {
    int i, x, y;
    initscr(); cbreak(); noecho();
    printw("press a key to start - you should see a 'rotating wheel' animation");
    getch();
    getmaxyx(stdscr, y, x);
    for (i = 0; i < 16; i++) {
      move(0, x-1);
      addch("\\-/|"[i%4]);
      refresh();
      sleep(1);
    }
    clear(); refresh(); endwin();
    return 0;
  }

however it actually produced output like "\-/|\-/|\-/|".
this is due to an optimization that does not move the terminal cursor if the
target position is the same as the supposedly current position.
supposedly, because the code that writes a single character does not increment
the internal cursor position, even though the terminal's cursor is advanced
by one through the write.
it is possible that the author of the code in question trusted in the domvcur()
function to do the bookkeeping for him, and wasn't aware of the optimization,
or vice versa the author of the optimization unaware of the usage of the
function for syncing the cursor position.

Author: rofl0r

libcurses/refresh.c

@@ -1238,6 +1238,9 @@ makech(int wy)
 #endif
 #else
 				if (WCOL(*nsp) > 0) {
+/* FIXME: putting a character advances the cursor, but the internal
+   housekeeping is not updated, this prevents from using the now commented
+   out optimization in domvcur(). */
 					__cputwchar((int) nsp->ch);
 #ifdef DEBUG
 					__CTRACE(__CTRACE_REFRESH,
@@ -1318,8 +1321,18 @@ domvcur(oy, ox, ny, nx)
 	    oy, ox, ny, nx );
 #endif /* DEBUG */
 	__unsetattr(1);
+/* FIXME: we have to turn off this optimization, because the internal cursor
+   position is not updated in makech() when putting a character.
+   eventually this optimization was not here when the other code was written,
+   so the author assumed that calling domvcur() would take care of that.
+   this causes breakage in a loop like:
+   for(i...) { move(0, 0); addch("\\-/|"[i%4]); refresh(); sleep(1); }
+   which is supposed to create a rotating wheel animation, but actually wrote
+   "\-/|\-/|\-/|\-/|\-/|" etc to the screen since the move() call turned NOP. */
+#if 0
 	if ( oy == ny && ox == nx )
 		return;
+#endif
 	__mvcur(oy, ox, ny, nx, 1);
 }