The TODONE file

While looking through old files, I found a TODO list so old that I've actually done most of the things on it. Usually these things double in size every year. I shall celebrate with a mocha. ( Details below the cut, if anyone cares. )

If only all of my projects were this close to completion

I finally got my Javascript implementation of Craig Reynolds's boids algorithm to work. Here is the relevant code:

var weights= new Array(1.0, 1.0, 1.0);

sepvect = sepvect.multiply(weights[0]);
alivect = alivect.multiply(weights[1]);
cohvect = cohvect.multiply(weights[2]);

I just needed to record magnitudes for one run and fiddle with the weights. (0.5,1.0,0.2) seemed to do the trick, though I should test with different numbers of boids to see if the magnitudes are relative to that variable.

As regards "finally", I started on this so long ago that I forget when and have intermittently picked it up and re-abandoned it since then. The oldest timestamp that I can find for it is 2006, but I think it goes back to 2003 or 2004 when it was going to be something that I would put together during spring break. The biggest problem was a trig error that I fixed last month after having almost fixed it earlier, causing directions to be wrong in one or two of the four quadrants.

.htaccess variables

You can set variables inside an Apache .htaccess file. To copy directly from someone else's example:

 RewriteCond  %{REQUEST_URI}  ^/category_abc/ 
 RewriteRule .* - [E=cat_id:1] 

 RewriteCond  %{REQUEST_URI}  ^/category_def/ 
 RewriteRule .* - [E=cat_id:2]

 - The E= tells Apache we're creating a new ENV variable. 
 - The cat_id is the name of the variable we're creating 
 - The :x is the value of the variable (simple key : value syntax).

And from another example:

RewriteCond %{HTTP:Accept-Language} ^.*(de|es|fr|it|ja|ru|en).*$ [NC]
RewriteRule ^(.*)$ - [env=lang:%1]
Set lang var to URI
RewriteEngine On
RewriteBase /
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /(.+)/(de|es|fr|it|ja|ru|en)/\ HTTP/ [NC]
RewriteRule ^(.*)$ - [env=lang:%2]

Environment variables are referenced as %{ENV:varname}. How they are used is another story. There are places you can't use them.

# Make a variable for RewriteBase
RewriteCond "/base_dir/" ^(.*)$
RewriteRule ^(.*)$ - [E=RewriteBase:%1]
# Fails, causes an internal server error.
RewriteBase %{ENV:RewriteBase}

You can't do this either:

# RequestPrefix is a previously declared variable. 
RewriteCond %{REQUEST_URI} ^%{ENV:RequestPrefix}(.*)$
RewriteRule ^(.*)$ - [E=RequestSuffix:%1]

A quick web search finds someone claiming that rewrite condition patterns are compiled before variables are interpreted.