sprixel: damage only on sprite_wipe() failure

src/lib/render.c

@@ -153,7 +153,7 @@ paint_sprixel(ncplane* p, struct crender* rvec, int starty, int startx,
       if(crender->p || crender->s.bgblends){
         // if sprite_wipe_cell() fails, we presumably do not have the
         // ability to wipe, and must reprint the character
-        if(sprite_wipe(nc, p->sprite, y, x)){
+        if(sprite_wipe(nc, p->sprite, y, x) < 0){
 //fprintf(stderr, "damaging due to wipe [%s] %d/%d\n", nccell_extended_gcluster(crender->p, &crender->c), absy, absx);
           crender->s.damaged = 1;
         }

src/lib/sixel.c

@@ -241,6 +241,11 @@ int sixel_wipe(sprixel* s, int ycell, int xcell){
   change_p2(s->glyph.buf, SIXEL_P2_TRANS);
   assert(NULL == s->n->tam[s->dimx * ycell + xcell].auxvector);
   s->n->tam[s->dimx * ycell + xcell].auxvector = auxvec;
+  // FIXME this invalidation ought not be necessary, since we're simply
+  // wiping, and thus a glyph is going to be printed over whatever we've
+  // just destroyed. in alacritty, however, this isn't sufficient to knock
+  // out a graphic; we need repaint with the transparency.
+  // see https://github.com/dankamongmen/notcurses/issues/2142
   int absx, absy;
   ncplane_abs_yx(s->n, &absy, &absx);
   sprixel_invalidate(s, absy, absx);