define pixel_scroll(), call it from rendering #2010

src/lib/render.c

@@ -887,6 +887,9 @@ rasterize_scrolls(ncpile* p, fbuf* f){
       p->nc->rstate.logendx = 0;
     }
   }
+  if(p->nc->tcache.pixel_scroll){
+    p->nc->tcache.pixel_scroll(&p->nc->tcache, p->scrolls);
+  }
   if(goto_location(p->nc, f, p->dimy, 0)){
     return -1;
   }

src/lib/termdesc.h

@@ -163,6 +163,8 @@ typedef struct tinfo {
   int (*pixel_clear_all)(fbuf* f);  // called during context startup
   // make a loaded graphic visible. only used with kitty.
   int (*pixel_commit)(fbuf* f, struct sprixel* s, unsigned noscroll);
+  // scroll all graphics up. only used with fbcon.
+  void (*pixel_scroll)(const struct tinfo*, int rows);
   uint8_t* (*pixel_trans_auxvec)(const struct tinfo* ti); // create tranparent auxvec
   // sprixel parameters. there are several different sprixel protocols, of
   // which we support sixel and kitty. the kitty protocol is used based