linux/Documentation/fb/internals.rst
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   1=============================
   2Frame Buffer device internals
   3=============================
   4
   5This is a first start for some documentation about frame buffer device
   6internals.
   7
   8Authors:
   9
  10- Geert Uytterhoeven <geert@linux-m68k.org>, 21 July 1998
  11- James Simmons <jsimmons@user.sf.net>, Nov 26 2002
  12
  13--------------------------------------------------------------------------------
  14
  15Structures used by the frame buffer device API
  16==============================================
  17
  18The following structures play a role in the game of frame buffer devices. They
  19are defined in <linux/fb.h>.
  20
  211. Outside the kernel (user space)
  22
  23  - struct fb_fix_screeninfo
  24
  25    Device independent unchangeable information about a frame buffer device and
  26    a specific video mode. This can be obtained using the FBIOGET_FSCREENINFO
  27    ioctl.
  28
  29  - struct fb_var_screeninfo
  30
  31    Device independent changeable information about a frame buffer device and a
  32    specific video mode. This can be obtained using the FBIOGET_VSCREENINFO
  33    ioctl, and updated with the FBIOPUT_VSCREENINFO ioctl. If you want to pan
  34    the screen only, you can use the FBIOPAN_DISPLAY ioctl.
  35
  36  - struct fb_cmap
  37
  38    Device independent colormap information. You can get and set the colormap
  39    using the FBIOGETCMAP and FBIOPUTCMAP ioctls.
  40
  41
  422. Inside the kernel
  43
  44  - struct fb_info
  45
  46    Generic information, API and low level information about a specific frame
  47    buffer device instance (slot number, board address, ...).
  48
  49  - struct `par`
  50
  51    Device dependent information that uniquely defines the video mode for this
  52    particular piece of hardware.
  53
  54
  55Visuals used by the frame buffer device API
  56===========================================
  57
  58
  59Monochrome (FB_VISUAL_MONO01 and FB_VISUAL_MONO10)
  60--------------------------------------------------
  61Each pixel is either black or white.
  62
  63
  64Pseudo color (FB_VISUAL_PSEUDOCOLOR and FB_VISUAL_STATIC_PSEUDOCOLOR)
  65---------------------------------------------------------------------
  66The whole pixel value is fed through a programmable lookup table that has one
  67color (including red, green, and blue intensities) for each possible pixel
  68value, and that color is displayed.
  69
  70
  71True color (FB_VISUAL_TRUECOLOR)
  72--------------------------------
  73The pixel value is broken up into red, green, and blue fields.
  74
  75
  76Direct color (FB_VISUAL_DIRECTCOLOR)
  77------------------------------------
  78The pixel value is broken up into red, green, and blue fields, each of which
  79are looked up in separate red, green, and blue lookup tables.
  80
  81
  82Grayscale displays
  83------------------
  84Grayscale and static grayscale are special variants of pseudo color and static
  85pseudo color, where the red, green and blue components are always equal to
  86each other.
  87