projects / linux-2.6-block.git / blame
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| ab42b818 MCC |
1 | ============================= |
| 2 | Frame Buffer device internals | |
| 3 | ============================= | |
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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 | |
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12 | |
| 13 | -------------------------------------------------------------------------------- | |
| 14 | ||
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15 | Structures used by the frame buffer device API |
| 16 | ============================================== | |
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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` |
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50 | |
| 51 | Device dependent information that uniquely defines the video mode for this | |
| 52 | particular piece of hardware. | |
| 53 | ||
| 54 | ||
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55 | Visuals used by the frame buffer device API |
| 56 | =========================================== | |
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57 | |
| 58 | ||
| 59 | Monochrome (FB_VISUAL_MONO01 and FB_VISUAL_MONO10) | |
| ab42b818 | 60 | -------------------------------------------------- |
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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 |
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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. |