VOID & PVOD can be set to only eat/not eat certain things

src/powder.c

@@ -344,6 +344,7 @@ int try_move(int i, int x, int y, int nx, int ny)
 	}
 	if ((r&0xFF)==PT_VOID || (r&0xFF)==PT_PVOD) //this is where void eats particles
 	{
+		if(!parts[r>>8].ctype || (parts[r>>8].ctype==parts[i].type)!=(parts[r>>8].tmp&1))
 			kill_part(i);
 		return 0;
 	}