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Name	Size	Permission
api.txt.gz	3.81 KB	-rw-r--r--
arkfb.txt	1.98 KB	-rw-r--r--
aty128fb.txt	2.07 KB	-rw-r--r--
cirrusfb.txt	1.89 KB	-rw-r--r--
cmap_xfbdev.txt	1.88 KB	-rw-r--r--
deferred_io.txt	2.96 KB	-rw-r--r--
efifb.txt	593 B	-rw-r--r--
ep93xx-fb.txt.gz	1.68 KB	-rw-r--r--
fbcon.txt.gz	4.27 KB	-rw-r--r--
framebuffer.txt.gz	4.84 KB	-rw-r--r--
gxfb.txt	1.19 KB	-rw-r--r--
imacfb.txt	600 B	-rw-r--r--
intel810.txt.gz	3.48 KB	-rw-r--r--
intelfb.txt	3.66 KB	-rw-r--r--
internals.txt	2.58 KB	-rw-r--r--
lxfb.txt	1.19 KB	-rw-r--r--
matroxfb.txt.gz	7.02 KB	-rw-r--r--
metronomefb.txt	1.95 KB	-rw-r--r--
modedb.txt.gz	2.87 KB	-rw-r--r--
pvr2fb.txt	2.19 KB	-rw-r--r--
pxafb.txt.gz	2.1 KB	-rw-r--r--
s3fb.txt	2.55 KB	-rw-r--r--
sa1100fb.txt	1.34 KB	-rw-r--r--
sh7760fb.txt.gz	1.95 KB	-rw-r--r--
sisfb.txt.gz	2.73 KB	-rw-r--r--
sm501.txt	290 B	-rw-r--r--
sm712fb.txt	752 B	-rw-r--r--
sstfb.txt.gz	3.19 KB	-rw-r--r--
tgafb.txt	2.37 KB	-rw-r--r--
tridentfb.txt	2.59 KB	-rw-r--r--
udlfb.txt.gz	3.09 KB	-rw-r--r--
uvesafb.txt.gz	2.83 KB	-rw-r--r--
vesafb.txt.gz	2.77 KB	-rw-r--r--
viafb.txt.gz	3.07 KB	-rw-r--r--
vt8623fb.txt	1.8 KB	-rw-r--r--

Code Editor : cmap_xfbdev.txt

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.

${this.title}

Code Editor : cmap_xfbdev.txt