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Diffstat (limited to 'Documentation/fb/cmap_xfbdev.txt')
-rw-r--r-- | Documentation/fb/cmap_xfbdev.txt | 53 |
1 files changed, 0 insertions, 53 deletions
diff --git a/Documentation/fb/cmap_xfbdev.txt b/Documentation/fb/cmap_xfbdev.txt deleted file mode 100644 index 55e1f0a3d2b..00000000000 --- a/Documentation/fb/cmap_xfbdev.txt +++ /dev/null @@ -1,53 +0,0 @@ -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. - |