projects / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 1da177e4 LT |
1 | |
| 2 | This is a first start for some documentation about frame buffer device | |
| 3 | internals. | |
| 4 | ||
| 5 | Geert Uytterhoeven <[email protected]>, 21 July 1998 | |
| 6 | James Simmons <[email protected]>, 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 |