| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 | |