this is how /sys/src/cmd/vnc/draw.c was changed to not "mouse turd" on
vesa.  have put the changed file in contrib at:
/n/sources/contrib/cinap_lenrek/draw.c

didnt made a patch because its just a work arround, not a real fix.

cpu% diff -c /n/dump/2009/0923/sys/src/cmd/vnc/draw.c draw.c
/n/dump/2009/0923/sys/src/cmd/vnc/draw.c:107,112 - draw.c:107,113
  updatescreen(Rectangle r)
  {
  	int b, bb;
+ 	Image *i;

  	lockdisplay(display);
  	if(r.max.x > Dx(screen->r) || r.max.y > Dy(screen->r)){
/n/dump/2009/0923/sys/src/cmd/vnc/draw.c:117,129 - draw.c:118,138
  		}
  	}

+ 	b = Dx(r) * pixb * Dy(r);
+
+ 	if(i = allocimage(display, r, screen->chan, 0, DNofill)){
+ 		loadimage(i, r, pixbuf, b);
+ 		draw(screen, rectaddpt(r, screen->r.min), i, nil, r.min);
+ 		freeimage(i);
+ 	}
+
  	/*
  	 * assume load image fails only because of resize
- 	 */
- 	b = Dx(r) * pixb * Dy(r);
  	bb = loadimage(screen, rectaddpt(r, screen->r.min), pixbuf, b);
  	if(bb != b && verbose)
  		fprint(2, "loadimage %d on %R for %R returned %d: %r\n", b, rectaddpt(r, screen->r.min), screen->r, bb);
+ 	 */
+
  	unlockdisplay(display);
  }

--
cinap