Commit | Line | Data |
---|---|---|
ab42b818 MCC |
1 | ============================= |
2 | Frame Buffer device internals | |
3 | ============================= | |
1da177e4 LT |
4 | |
5 | This is a first start for some documentation about frame buffer device | |
6 | internals. | |
7 | ||
ab42b818 MCC |
8 | Authors: |
9 | ||
10 | - Geert Uytterhoeven <geert@linux-m68k.org>, 21 July 1998 | |
11 | - James Simmons <jsimmons@user.sf.net>, Nov 26 2002 | |
1da177e4 LT |
12 | |
13 | -------------------------------------------------------------------------------- | |
14 | ||
ab42b818 MCC |
15 | Structures used by the frame buffer device API |
16 | ============================================== | |
1da177e4 LT |
17 | |
18 | The following structures play a role in the game of frame buffer devices. They | |
19 | are defined in <linux/fb.h>. | |
20 | ||
21 | 1. 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 | ||
42 | 2. 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 | ||
ab42b818 | 49 | - struct `par` |
1da177e4 LT |
50 | |
51 | Device dependent information that uniquely defines the video mode for this | |
52 | particular piece of hardware. | |
53 | ||
54 | ||
ab42b818 MCC |
55 | Visuals used by the frame buffer device API |
56 | =========================================== | |
1da177e4 LT |
57 | |
58 | ||
59 | Monochrome (FB_VISUAL_MONO01 and FB_VISUAL_MONO10) | |
ab42b818 | 60 | -------------------------------------------------- |
1da177e4 LT |
61 | Each pixel is either black or white. |
62 | ||
63 | ||
64 | Pseudo color (FB_VISUAL_PSEUDOCOLOR and FB_VISUAL_STATIC_PSEUDOCOLOR) | |
65 | --------------------------------------------------------------------- | |
66 | The whole pixel value is fed through a programmable lookup table that has one | |
67 | color (including red, green, and blue intensities) for each possible pixel | |
68 | value, and that color is displayed. | |
69 | ||
70 | ||
71 | True color (FB_VISUAL_TRUECOLOR) | |
72 | -------------------------------- | |
73 | The pixel value is broken up into red, green, and blue fields. | |
74 | ||
75 | ||
76 | Direct color (FB_VISUAL_DIRECTCOLOR) | |
77 | ------------------------------------ | |
ab42b818 | 78 | The pixel value is broken up into red, green, and blue fields, each of which |
1da177e4 LT |
79 | are looked up in separate red, green, and blue lookup tables. |
80 | ||
81 | ||
82 | Grayscale displays | |
83 | ------------------ | |
84 | Grayscale and static grayscale are special variants of pseudo color and static | |
85 | pseudo color, where the red, green and blue components are always equal to | |
86 | each other. |