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author | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 18:20:36 -0400 |
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committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 18:20:36 -0400 |
commit | 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch) | |
tree | 0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/fb/internals.txt |
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
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1 | |||
2 | This is a first start for some documentation about frame buffer device | ||
3 | internals. | ||
4 | |||
5 | Geert Uytterhoeven <geert@linux-m68k.org>, 21 July 1998 | ||
6 | James Simmons <jsimmons@user.sf.net>, Nov 26 2002 | ||
7 | |||
8 | -------------------------------------------------------------------------------- | ||
9 | |||
10 | *** STRUCTURES USED BY THE FRAME BUFFER DEVICE API *** | ||
11 | |||
12 | The following structures play a role in the game of frame buffer devices. They | ||
13 | are defined in <linux/fb.h>. | ||
14 | |||
15 | 1. Outside the kernel (user space) | ||
16 | |||
17 | - struct fb_fix_screeninfo | ||
18 | |||
19 | Device independent unchangeable information about a frame buffer device and | ||
20 | a specific video mode. This can be obtained using the FBIOGET_FSCREENINFO | ||
21 | ioctl. | ||
22 | |||
23 | - struct fb_var_screeninfo | ||
24 | |||
25 | Device independent changeable information about a frame buffer device and a | ||
26 | specific video mode. This can be obtained using the FBIOGET_VSCREENINFO | ||
27 | ioctl, and updated with the FBIOPUT_VSCREENINFO ioctl. If you want to pan | ||
28 | the screen only, you can use the FBIOPAN_DISPLAY ioctl. | ||
29 | |||
30 | - struct fb_cmap | ||
31 | |||
32 | Device independent colormap information. You can get and set the colormap | ||
33 | using the FBIOGETCMAP and FBIOPUTCMAP ioctls. | ||
34 | |||
35 | |||
36 | 2. Inside the kernel | ||
37 | |||
38 | - struct fb_info | ||
39 | |||
40 | Generic information, API and low level information about a specific frame | ||
41 | buffer device instance (slot number, board address, ...). | ||
42 | |||
43 | - struct `par' | ||
44 | |||
45 | Device dependent information that uniquely defines the video mode for this | ||
46 | particular piece of hardware. | ||
47 | |||
48 | |||
49 | -------------------------------------------------------------------------------- | ||
50 | |||
51 | *** VISUALS USED BY THE FRAME BUFFER DEVICE API *** | ||
52 | |||
53 | |||
54 | Monochrome (FB_VISUAL_MONO01 and FB_VISUAL_MONO10) | ||
55 | ------------------------------------------------- | ||
56 | Each pixel is either black or white. | ||
57 | |||
58 | |||
59 | Pseudo color (FB_VISUAL_PSEUDOCOLOR and FB_VISUAL_STATIC_PSEUDOCOLOR) | ||
60 | --------------------------------------------------------------------- | ||
61 | The whole pixel value is fed through a programmable lookup table that has one | ||
62 | color (including red, green, and blue intensities) for each possible pixel | ||
63 | value, and that color is displayed. | ||
64 | |||
65 | |||
66 | True color (FB_VISUAL_TRUECOLOR) | ||
67 | -------------------------------- | ||
68 | The pixel value is broken up into red, green, and blue fields. | ||
69 | |||
70 | |||
71 | Direct color (FB_VISUAL_DIRECTCOLOR) | ||
72 | ------------------------------------ | ||
73 | The pixel value is broken up into red, green, and blue fields, each of which | ||
74 | are looked up in separate red, green, and blue lookup tables. | ||
75 | |||
76 | |||
77 | Grayscale displays | ||
78 | ------------------ | ||
79 | Grayscale and static grayscale are special variants of pseudo color and static | ||
80 | pseudo color, where the red, green and blue components are always equal to | ||
81 | each other. | ||
82 | |||