ncvisual_render_pixels: reject negative placex/placey on alignment #1526

src/lib/internal.h

@@ -1252,6 +1252,8 @@ plane_blit_sixel(sprixel* spx, char* s, int bytes, int rows, int cols,
   }
   ncplane* n = spx->n;
   uint32_t gcluster = htole(0x02000000ul) + htole(spx->id);
+  // FIXME rows/cols ought never exceed the size, just as placey/placex
+  // ought never be negative. why need we check the former?
   for(int y = placey ; y < placey + rows && y < ncplane_dim_y(n) ; ++y){
     for(int x = placex ; x < placex + cols && x < ncplane_dim_x(n) ; ++x){
       nccell* c = ncplane_cell_ref_yx(n, y, x);

src/lib/visual.c

@@ -652,6 +652,9 @@ ncplane* ncvisual_render_pixels(notcurses* nc, ncvisual* ncv, const struct blits
     }else if(placex == NCALIGN_RIGHT){
       placex = ncplane_dim_x(n) - dispcols / nc->tcache.cellpixx;
     }
+    if(placex < 0){
+      return NULL;
+    }
   }
   if(flags & NCVISUAL_OPTION_VERALIGNED){
     if(placey == NCALIGN_CENTER){
@@ -659,6 +662,9 @@ ncplane* ncvisual_render_pixels(notcurses* nc, ncvisual* ncv, const struct blits
     }else if(placey == NCALIGN_BOTTOM){
       placey = ncplane_dim_y(n) * nc->tcache.cellpixy - disprows / nc->tcache.cellpixy;
     }
+    if(placey < 0){
+      return NULL;
+    }
   }
 //fprintf(stderr, "pblit: %dx%d <- %dx%d of %d/%d stride %u @%dx%d %p %u\n", disprows, dispcols, begy, begx, ncv->rows, ncv->cols, ncv->rowstride, placey, placex, ncv->data, nc->tcache.cellpixx);
   blitterargs bargs;