From 76cb841cb886eef6b3bee341a2266c76578724ad Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 6 May 2024 03:02:30 +0200 Subject: Adding upstream version 4.19.249. Signed-off-by: Daniel Baumann --- Documentation/fb/internals.txt | 82 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 82 insertions(+) create mode 100644 Documentation/fb/internals.txt (limited to 'Documentation/fb/internals.txt') diff --git a/Documentation/fb/internals.txt b/Documentation/fb/internals.txt new file mode 100644 index 000000000..9b2a2b2f3 --- /dev/null +++ b/Documentation/fb/internals.txt @@ -0,0 +1,82 @@ + +This is a first start for some documentation about frame buffer device +internals. + +Geert Uytterhoeven , 21 July 1998 +James Simmons , 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 . + +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. + -- cgit v1.2.3