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86 lines
2.7 KiB
86 lines
2.7 KiB
============================= |
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Frame Buffer device internals |
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============================= |
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This is a first start for some documentation about frame buffer device |
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internals. |
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Authors: |
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- Geert Uytterhoeven <[email protected]>, 21 July 1998 |
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- James Simmons <[email protected]>, Nov 26 2002 |
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-------------------------------------------------------------------------------- |
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Structures used by the frame buffer device API |
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============================================== |
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The following structures play a role in the game of frame buffer devices. They |
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are defined in <linux/fb.h>. |
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1. Outside the kernel (user space) |
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- struct fb_fix_screeninfo |
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Device independent unchangeable information about a frame buffer device and |
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a specific video mode. This can be obtained using the FBIOGET_FSCREENINFO |
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ioctl. |
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- struct fb_var_screeninfo |
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Device independent changeable information about a frame buffer device and a |
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specific video mode. This can be obtained using the FBIOGET_VSCREENINFO |
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ioctl, and updated with the FBIOPUT_VSCREENINFO ioctl. If you want to pan |
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the screen only, you can use the FBIOPAN_DISPLAY ioctl. |
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- struct fb_cmap |
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Device independent colormap information. You can get and set the colormap |
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using the FBIOGETCMAP and FBIOPUTCMAP ioctls. |
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2. Inside the kernel |
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- struct fb_info |
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Generic information, API and low level information about a specific frame |
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buffer device instance (slot number, board address, ...). |
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- struct `par` |
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Device dependent information that uniquely defines the video mode for this |
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particular piece of hardware. |
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Visuals used by the frame buffer device API |
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=========================================== |
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Monochrome (FB_VISUAL_MONO01 and FB_VISUAL_MONO10) |
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-------------------------------------------------- |
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Each pixel is either black or white. |
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Pseudo color (FB_VISUAL_PSEUDOCOLOR and FB_VISUAL_STATIC_PSEUDOCOLOR) |
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--------------------------------------------------------------------- |
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The whole pixel value is fed through a programmable lookup table that has one |
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color (including red, green, and blue intensities) for each possible pixel |
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value, and that color is displayed. |
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True color (FB_VISUAL_TRUECOLOR) |
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-------------------------------- |
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The pixel value is broken up into red, green, and blue fields. |
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Direct color (FB_VISUAL_DIRECTCOLOR) |
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------------------------------------ |
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The pixel value is broken up into red, green, and blue fields, each of which |
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are looked up in separate red, green, and blue lookup tables. |
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Grayscale displays |
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------------------ |
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Grayscale and static grayscale are special variants of pseudo color and static |
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pseudo color, where the red, green and blue components are always equal to |
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each other.
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