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1da177e4c   Linus Torvalds   Linux-2.6.12-rc2 
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  This is a first start for some documentation about frame buffer device
  internals.
  
  Geert Uytterhoeven <geert@linux-m68k.org>, 21 July 1998
  James Simmons <jsimmons@user.sf.net>, Nov 26 2002
  
  --------------------------------------------------------------------------------
  
  	    ***  STRUCTURES USED BY THE FRAME BUFFER DEVICE API  ***
  
  The following structures play a role in the game of frame buffer devices. They
  are defined in <linux/fb.h>.
  
  1. Outside the kernel (user space)
  
    - struct fb_fix_screeninfo
  
      Device independent unchangeable information about a frame buffer device and
      a specific video mode. This can be obtained using the FBIOGET_FSCREENINFO
      ioctl.
  
    - struct fb_var_screeninfo
  
      Device independent changeable information about a frame buffer device and a
      specific video mode. This can be obtained using the FBIOGET_VSCREENINFO
      ioctl, and updated with the FBIOPUT_VSCREENINFO ioctl. If you want to pan
      the screen only, you can use the FBIOPAN_DISPLAY ioctl.
  
    - struct fb_cmap
  
      Device independent colormap information. You can get and set the colormap
      using the FBIOGETCMAP and FBIOPUTCMAP ioctls.
  
  
  2. Inside the kernel
  
    - struct fb_info
  
      Generic information, API and low level information about a specific frame
      buffer device instance (slot number, board address, ...).
  
    - struct `par'
  
      Device dependent information that uniquely defines the video mode for this
      particular piece of hardware.
  
  
  --------------------------------------------------------------------------------
  
  	    ***  VISUALS USED BY THE FRAME BUFFER DEVICE API  ***
  
  
  Monochrome (FB_VISUAL_MONO01 and FB_VISUAL_MONO10)
  -------------------------------------------------
  Each pixel is either black or white.
  
  
  Pseudo color (FB_VISUAL_PSEUDOCOLOR and FB_VISUAL_STATIC_PSEUDOCOLOR)
  ---------------------------------------------------------------------
  The whole pixel value is fed through a programmable lookup table that has one
  color (including red, green, and blue intensities) for each possible pixel
  value, and that color is displayed.
  
  
  True color (FB_VISUAL_TRUECOLOR)
  --------------------------------
  The pixel value is broken up into red, green, and blue fields.
  
  
  Direct color (FB_VISUAL_DIRECTCOLOR)
  ------------------------------------
  The pixel value is broken up into red, green, and blue fields, each of which 
  are looked up in separate red, green, and blue lookup tables.
  
  
  Grayscale displays
  ------------------
  Grayscale and static grayscale are special variants of pseudo color and static
  pseudo color, where the red, green and blue components are always equal to
  each other.