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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.
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