diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-09 22:34:26 +0300 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-09 22:34:26 +0300 |
commit | e9a83bd2322035ed9d7dcf35753d3f984d76c6a5 (patch) | |
tree | 66dc466ff9aec0f9bb7f39cba50a47eab6585559 /Documentation/fb/cmap_xfbdev.rst | |
parent | 7011b7e1b702cc76f9e969b41d9a95969f2aecaa (diff) | |
parent | 454f96f2b738374da4b0a703b1e2e7aed82c4486 (diff) | |
download | linux-e9a83bd2322035ed9d7dcf35753d3f984d76c6a5.tar.xz |
Merge tag 'docs-5.3' of git://git.lwn.net/linux
Pull Documentation updates from Jonathan Corbet:
"It's been a relatively busy cycle for docs:
- A fair pile of RST conversions, many from Mauro. These create more
than the usual number of simple but annoying merge conflicts with
other trees, unfortunately. He has a lot more of these waiting on
the wings that, I think, will go to you directly later on.
- A new document on how to use merges and rebases in kernel repos,
and one on Spectre vulnerabilities.
- Various improvements to the build system, including automatic
markup of function() references because some people, for reasons I
will never understand, were of the opinion that
:c:func:``function()`` is unattractive and not fun to type.
- We now recommend using sphinx 1.7, but still support back to 1.4.
- Lots of smaller improvements, warning fixes, typo fixes, etc"
* tag 'docs-5.3' of git://git.lwn.net/linux: (129 commits)
docs: automarkup.py: ignore exceptions when seeking for xrefs
docs: Move binderfs to admin-guide
Disable Sphinx SmartyPants in HTML output
doc: RCU callback locks need only _bh, not necessarily _irq
docs: format kernel-parameters -- as code
Doc : doc-guide : Fix a typo
platform: x86: get rid of a non-existent document
Add the RCU docs to the core-api manual
Documentation: RCU: Add TOC tree hooks
Documentation: RCU: Rename txt files to rst
Documentation: RCU: Convert RCU UP systems to reST
Documentation: RCU: Convert RCU linked list to reST
Documentation: RCU: Convert RCU basic concepts to reST
docs: filesystems: Remove uneeded .rst extension on toctables
scripts/sphinx-pre-install: fix out-of-tree build
docs: zh_CN: submitting-drivers.rst: Remove a duplicated Documentation/
Documentation: PGP: update for newer HW devices
Documentation: Add section about CPU vulnerabilities for Spectre
Documentation: platform: Delete x86-laptop-drivers.txt
docs: Note that :c:func: should no longer be used
...
Diffstat (limited to 'Documentation/fb/cmap_xfbdev.rst')
-rw-r--r-- | Documentation/fb/cmap_xfbdev.rst | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/Documentation/fb/cmap_xfbdev.rst b/Documentation/fb/cmap_xfbdev.rst new file mode 100644 index 000000000000..5db5e9787361 --- /dev/null +++ b/Documentation/fb/cmap_xfbdev.rst @@ -0,0 +1,56 @@ +========================== +Understanding fbdev's cmap +========================== + +These notes explain how X's dix layer uses fbdev's cmap structures. + +- example of relevant structures in fbdev as used for a 3-bit grayscale cmap:: + + struct fb_var_screeninfo { + .bits_per_pixel = 8, + .grayscale = 1, + .red = { 4, 3, 0 }, + .green = { 0, 0, 0 }, + .blue = { 0, 0, 0 }, + } + struct fb_fix_screeninfo { + .visual = FB_VISUAL_STATIC_PSEUDOCOLOR, + } + for (i = 0; i < 8; i++) + info->cmap.red[i] = (((2*i)+1)*(0xFFFF))/16; + memcpy(info->cmap.green, info->cmap.red, sizeof(u16)*8); + memcpy(info->cmap.blue, info->cmap.red, sizeof(u16)*8); + +- X11 apps do something like the following when trying to use grayscale:: + + for (i=0; i < 8; i++) { + char colorspec[64]; + memset(colorspec,0,64); + sprintf(colorspec, "rgb:%x/%x/%x", i*36,i*36,i*36); + if (!XParseColor(outputDisplay, testColormap, colorspec, &wantedColor)) + printf("Can't get color %s\n",colorspec); + XAllocColor(outputDisplay, testColormap, &wantedColor); + grays[i] = wantedColor; + } + +There's also named equivalents like gray1..x provided you have an rgb.txt. + +Somewhere in X's callchain, this results in a call to X code that handles the +colormap. For example, Xfbdev hits the following: + +xc-011010/programs/Xserver/dix/colormap.c:: + + FindBestPixel(pentFirst, size, prgb, channel) + + dr = (long) pent->co.local.red - prgb->red; + dg = (long) pent->co.local.green - prgb->green; + db = (long) pent->co.local.blue - prgb->blue; + sq = dr * dr; + UnsignedToBigNum (sq, &sum); + BigNumAdd (&sum, &temp, &sum); + +co.local.red are entries that were brought in through FBIOGETCMAP which come +directly from the info->cmap.red that was listed above. The prgb is the rgb +that the app wants to match to. The above code is doing what looks like a least +squares matching function. That's why the cmap entries can't be set to the left +hand side boundaries of a color range. |