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