#define gray_width 16
#define gray_height 16
static char gray_bits[] = {
   0xaa, 0xaa, 0x55, 0x55, 0xaa, 0xaa, 0x55, 0x55, 0xaa, 0xaa, 0x55, 0x55,
   0xaa, 0xaa, 0x55, 0x55, 0xaa, 0xaa, 0x55, 0x55, 0xaa, 0xaa, 0x55, 0x55,
   0xaa, 0xaa, 0x55, 0x55, 0xaa, 0xaa, 0x55, 0x55};