#define wall_width 16
#define wall_height 16
static char wall_bits[] = {
   0xff, 0xff, 0x5d, 0x55, 0xba, 0xaa, 0x5d, 0x55, 0xba, 0xaa, 0x5d, 0x55,
   0xba, 0xaa, 0xff, 0xff, 0xff, 0xff, 0x55, 0x5d, 0xaa, 0xba, 0x55, 0x5d,
   0xaa, 0xba, 0x55, 0x5d, 0xaa, 0xba, 0xff, 0xff};