Is there a limit on how many times mt_rand() or rand() can be called?

kolanos

In one script I mean. For example, I wrote a script that creates an x,y array (64x64) and I was using GDlib to put together a grid based on this array. Then, just for kicks, I wanted to assign a random color to each block within this grid (4096 total) which meant a call to the mt_rand() 4,096 times. However, when I ran the script it only generated a random color 253/254 times and left the remaining blocks a solid (the last random color generated).

Attached is an example of what I see. Anyone know what might be causing this? Is there a limit on how many times a random number generator can be used in one script?

kolanos

I've been tweaking my code a bit and now am not so sure that it is mt_rand() that is the problem, but instead imagecolorallocate().

Can imagecolorallocate() only be called 255 or so times in a script?

section31

Originally posted by kolanos
I've been tweaking my code a bit and now am not so sure that it is mt_rand() that is the problem, but instead imagecolorallocate().

Can imagecolorallocate() only be called 255 or so times in a script?

NOt sure...but it works fine on my end.

http://section31.us/temp/test.php

http://section31.us/temp/test.php?source

kolanos

Originally posted by section31
NOt sure...but it works fine on my end.

http://section31.us/temp/test.php

http://section31.us/temp/test.php?source

I have pretty much eliminated mt_rand() as the culprit. Now I am thinking it is imagecolorallocate() that is limiting the colors to 255 or so.

My first thought was that it was an image format problem (ie. GIFs being limited to 255 colors) -- but I was using PNG for this script and I tried generating a JPEG and got the same result.

No idea why imagecolorallocate() would limit the colors that can be generated if the image format wasn't an issue.

tekky

if you look on php.net....

bisqwit at iki dot fi
16-Feb-2002 09:30
Actually, you can't allocate more than 256 colours for an paletted image (ImageCreate).
Use ImageCreateTrueColor instead. For it to work, you need libgd version 2 support in php though.
bisqwit at iki dot fi
16-Feb-2002 02:20
Looks like this function only allows allocating of 256 distinct colours.
?
So this code:
<?php
$im = ImageCreate(500,200);
for($a=0; $a<500; $a++)
{
$c = 128 + sin($a) * 127;
ImageLine($im, $a,0, $a,199, ImageColorAllocate($im, $c,$c,$c));
}
ob_start();
ImageJpeg($im, '', 75);
$s = ob_get_contents();
ob_end_clean();
?
header('Content-type: image/jpeg');
header('Content-length: '.strlen($s));
print $s;
?
will make an image that has changing colours at
the first 256 pixel columns only. The rest are gray.

kolanos

Originally posted by tekky
if you look on php.net....

I checked PHP.net and didn't spot that (I swear!).

Thanks for your help!