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palette256: Comment about "web-safe" colors.

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Kalle Olavi Niemitalo 2007-02-27 10:31:18 +02:00 committed by Kalle Olavi Niemitalo
parent 76be98030a
commit 0bd0dd160e
1 changed files with 29 additions and 1 deletions
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30
src/terminal/palette.inc
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@ -164,7 +164,35 @@ static const struct rgb palette88[] = {
/* Colors 0- 15 are the ANSI colors (from xterm-215/XTerm-col.ad
* and Xorg's rgb.txt, not the same as palette16[]).
* Colors 16-231 are a 6x6x6 color cube
* Colors 231-255 are a grayscale ramp (with black and white left out). */
* Colors 231-255 are a grayscale ramp (with black and white left out).
*
* The 6x6x6 color cube of xterm uses brightnesses 00-5f-87-af-d7-ff
* whereas the "web-safe" palette uses 00-33-66-99-cc-ff, which then
* becomes 00-5f-5f-87-d7-ff when ELinks finds the nearest available
* color. If it is important to preserve distinctions between
* "web-safe" colors, you can alter the 6x6x6 cube in palette256[] to
* make ELinks imagine the brightnesses are 00-33-66-99-cc-ff, so that
* the "web-safe" colors then fall directly on it. If you do this,
* you should also change the other entries of palette256[] in a
* similar way, to keep the brightnesses in the correct order. You
* could for instance interpolate the brightnesses with the following
* function, which passes through all six points and has a continuous
* positive first derivative:
*
* y = (765/11) - sqrt(585225/121 - (2601/55)*x) when x <= 0x5f
* x = (-55/2601)*y^2 + (150/51)*y when x <= 0x5f
* y = (51/40)*x + (-561/8) when x >= 0x5f
*
* If you use Emacs then here is how to do it easily:
*
* (while (re-search-forward "0x\\([[:xdigit:]]+\\)" nil t)
(let* ((x (string-to-number (match-string 1) 16))
(y (if (<= x #x5f)
(- (/ 765.0 11.0)
(sqrt (- (/ 585225.0 121.0) (* (/ 2601.0 55.0) x))))
(+ (* (/ 51.0 40.0) x) (/ -561.0 8.0)))))
(replace-match (format "%.2x" (round y)) nil t nil 1)))
*/
static const struct rgb palette256[] = {
{0x00, 0x00, 0x00}, /* 0 black */
{0xcd, 0x00, 0x00}, /* 1 red3 */