=============================
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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 <geert@linux-m68k.org>, 21 July 1998
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- James Simmons <jsimmons@user.sf.net>, 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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