struct fb_bitfield

struct fb_bitfield {   /*fb緩存的RGB位域，該結構描述每一個像素顯示緩衝區的組織方式，假如爲RGB565模式，R佔5位=bit[11:15] 
                                       G佔6位=bit[10:5] B佔5位=bit[4:0] */
  __u32 offset;        /* beginning of bitfield */  /*位域偏移:red=11 ,green=5 blue=0 */
  __u32 length;       /* length of bitfield  */  /*位域長度 red=5 green=6 blue=5 */
  __u32 msb_right; /* != 0 : Most significant bit is */  /*msb_right!=0=>MSB在右邊 */
      /* right */ 
 };