This is a first start for some documentation about frame buffer device internals. Geert Uytterhoeven <geert@linux-m68k.org>, 21 July 1998 James Simmons <jsimmons@user.sf.net>, Nov 26 2002 -------------------------------------------------------------------------------- *** STRUCTURES USED BY THE FRAME BUFFER DEVICE API *** The following structures play a role in the game of frame buffer devices. They are defined in <linux/fb.h>. 1. Outside the kernel (user space) - struct fb_fix_screeninfo Device independent unchangeable information about a frame buffer device and a specific video mode. This can be obtained using the FBIOGET_FSCREENINFO ioctl. - struct fb_var_screeninfo Device independent changeable information about a frame buffer device and a specific video mode. This can be obtained using the FBIOGET_VSCREENINFO ioctl, and updated with the FBIOPUT_VSCREENINFO ioctl. If you want to pan the screen only, you can use the FBIOPAN_DISPLAY ioctl. - struct fb_cmap Device independent colormap information. You can get and set the colormap using the FBIOGETCMAP and FBIOPUTCMAP ioctls. 2. Inside the kernel - struct fb_info Generic information, API and low level information about a specific frame buffer device instance (slot number, board address, ...). - struct `par' Device dependent information that uniquely defines the video mode for this particular piece of hardware. -------------------------------------------------------------------------------- *** VISUALS USED BY THE FRAME BUFFER DEVICE API *** Monochrome (FB_VISUAL_MONO01 and FB_VISUAL_MONO10) ------------------------------------------------- Each pixel is either black or white. Pseudo color (FB_VISUAL_PSEUDOCOLOR and FB_VISUAL_STATIC_PSEUDOCOLOR) --------------------------------------------------------------------- The whole pixel value is fed through a programmable lookup table that has one color (including red, green, and blue intensities) for each possible pixel value, and that color is displayed. True color (FB_VISUAL_TRUECOLOR) -------------------------------- The pixel value is broken up into red, green, and blue fields. Direct color (FB_VISUAL_DIRECTCOLOR) ------------------------------------ The pixel value is broken up into red, green, and blue fields, each of which are looked up in separate red, green, and blue lookup tables. Grayscale displays ------------------ Grayscale and static grayscale are special variants of pseudo color and static pseudo color, where the red, green and blue components are always equal to each other.