#define gray_width 16
#define gray_height 16
static short gray_bits[] = {
   0xaaaa, 0x5555, 0xaaaa, 0x5555,
   0xaaaa, 0x5555, 0xaaaa, 0x5555,
   0xaaaa, 0x5555, 0xaaaa, 0x5555,
   0xaaaa, 0x5555, 0xaaaa, 0x5555};