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Zecho has asked for the wisdom of the Perl Monks concerning the following question:
This was inspired by a javascript I had seen somewhere once, and I found it quite usefull. So as a service to all non-javascript users (namely me) I wrote this perl version.
So to the point, it works! but... other than the non use of CGI.pm I think it still could be improved a bit.. please try it out on your machine or visit this demo so you can get the whole picture. Make sure you use the updated code
below, and not the first version. Any suggestions would be
greatly appreciated!
#!/usr/bin/perl -w
use strict;
my @nums = qw/00 20 40 60 80 A0 C0 FF/;
my $f=0;
my $g=0;
my $h=0;
print "Content-type: text/html\n\n";
print '<html><head><title>Web-Safe Colors</title><head>';
print '<body><table align=center border=0><tr><td>';
while($f<8) {
$g=0;
$h=0;
print '<table width=100% border=1 cellpadding=5>';
while ($g<8){
$h=0;
print "<tr>\n";
while ($h<8){
print "<td align=center bgcolor=\"\#$nums[$f]$nums[$g]
+$nums[$h]\">";
print "<font color=\"\#$nums[7-$f]$nums[7-$g]$nums[7-$
+h]\">";
print "$nums[$f]$nums[$g]$nums[$h]<\/font><\/td> ";
+
$h+=1; }
print '</tr>';
$g+=1;
}
print "<\/table>\n<p>";
$f+=1;
}
print '</td></tr></table></body></html>';
I plan to rewrite it using CGI as soon as I learn CGI. |
Re: Web-Safe Color Chart
by merlyn (Sage) on Oct 05, 2001 at 06:48 UTC
|
While not commenting on the rest of your code, at least you should learn that your line:
my @nums = qw/00 20 40 60 80 A0 C0 FF/;
is off. It should be:
my @nums = qw/00 33 66 99 CC FF/;
-- Randal L. Schwartz, Perl hacker | [reply]
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Re: Web-Safe Color Chart
by trantor (Chaplain) on Oct 05, 2001 at 06:57 UTC
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As far as I know, and as merlyn pointed out, a Web safe
palette should consist of 6 * 6 * 6 = 216 colours only.
Besides this, an obviuos improvement in the readability of
your code could be using foreach instead
of while loops, e.g.:
my @nums = qw/00 33 66 99 CC FF/;
foreach my $r (@nums) {
foreach my $g (@nums) {
foreach my $b (@nums) {
# Do something with $r, $g and $b
}
}
}
The usual way of representing this palette is either an
8 * 8 grid (using only the first 216 cells) or 6 tables,
6 * 6 each. The second approach is easier to program,
the first more compact.
Speaking about CGI.pm, since you don't process
input parameters, can't generate errors, always use the
same Content-type, there are no big security
concerns that should force you to use CGI
instead of rolling your own. Nonetheless it is a good
exercise and a good starting point for studying the module,
which should be customary for more complex CGIs.
-- TMTOWTDI | [reply]
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Re: Web-Safe Color Chart
by Zecho (Hermit) on Oct 05, 2001 at 07:25 UTC
|
ack... I don't know where I got those values.. (actually I do and am ashamed to admit it) I have recoded it to meet the spec and the corrected version is below. The demo has been updated to the new code as well
Thanks merlyn & trantor for pointing that out
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Sneaky glob trick (was Web-Safe Color Chart)
by blakem (Monsignor) on Oct 05, 2001 at 08:46 UTC
|
perl -e'print"$_\n"for glob("{00,20,40,60,80,A0,C0,FF}"x3);'
Update: trimmed a dozen chars thanks to CheeseLord
perl -le'print for glob"{00,33,66,99,CC,FF}"x3'
Update 2: I don't fully understand the meat of this myself (i think it came from tilly) If anyone knows
how this works, I'd actually love an explanation, especially since the glob docs aren't very helpful.
Update 3: Indeed it was tilly that showed me this trick. Original node at Re (tilly) 2: Sort of like a file handle, but not.
-Blake
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First of all, glob expands the pattern according to shell
conventions, so
glob "foob{a,b,c}r"
returns the list
('foobar', 'foobbr', 'foobcr')
just like bash would return 'foobar foobbr foobcr' expandig metacharacters
The x operator applied to a string repeats
the string the specified number of times, so
"{a,b,c}" x 3 evaluates as "{a,b,c}{a,b,c}{a,b,c}"
When you feed this expression to glob, the
result is a list of all the possible combinations of
a, b and c in a
string of three characters, from 'aaa' to
'ccc'.
This could be easily achieved through magical string
autoincrement, but the beauty of this method (very nice, I
love it!) is that it applies to any set of strings to
combine, not just characters.
-- TMTOWTDI
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Thanks for the explanation... I've searched in vain for the node where I originally found this trick. Here is the code i squirrled away from it though:
#!/usr/bin/perl
print map "$_\n", glob("{A,B,C}{a,b,c}");
I guess the part that puzzled me is that glob
*usually* interacts with the filesystem. glob("*.pl") will return list of perl scripts in your cwd.... why aren't the values above checked against the filesystem for actual files?
Update: The code above came from Re (tilly) 2: Sort of like a file handle, but not.
-Blake
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