How do I create VRML with PHP?

PHP is becoming very popular language for creating dynamic websites, particularly for generating them from databases. However, 2D websites are just boring, aren't they? What we want is a way to harness the power of PHP to create database-driven VRML worlds. Well, it's easier than you might think.

PHP can output any text information you like - the only thing that identifies the file type is the MIME type that gets sent by the web server before the file itself. Fortunately, in PHP, you can take control of this very information. All you have to do is send the VRML MIME type ("model/vrml"), and then write the appropriate VRML nodes. There are a few things you have to be careful of, but that's basically it.

Let's write a simple PHP file that generates an empty VRML world:

<?php
   header ("Content-type: model/vrml");
   echo "#VRML V2.0 utf8\n";
?>

The first line here is the important one. This uses the built-in PHP function header(), which sends HTTP headers. In this case, we want to send the Content-type header, which we set to the VRML MIME type, "model/vrml". The second simply uses echo() to write the standard VRML header, creating a valid VRML file.

Now, here's the first thing to be careful about. You can't send any output before the header() function is called, otherwise the headers will not be sent. A general rule is to make the header code the first thing in your PHP file, or at least make sure it's before anything that can print output. One common problem is that you may have included other files before the header() function call; if those files have a new line at the end, it counts as output, and will stop the header() working.

The second thing to be careful about is that some VRML browsers don't like whitespace before the VRML header. Therefore, you have to either print it out using echo as above, or make sure it's on the first non-PHP line in the file, as below. Printing it using echo is probably the best way.

Now that that's dealt with, you're away! Just like in HTML, you can mix PHP and normal VRML, like so:

<?php
   header ("Content-type: model/vrml");
   echo "#VRML V2.0 utf8\n";
?>

Shape {
   geometry Box {
   
<?php
   $size = 2;
   echo "      size $size $size $size \n";
?>

   }
}

The above example creates a pretty simple 2x2x2 box. And that's pretty much it for PHP and VRML. Of course, as with normal PHP, you can send whatever output you like. You can use URL arguments, so if you were to use the code below with a URL like http://www.my-domain.com/vrml.php?size=2,

<?php
   header ("Content-type: model/vrml");
   echo "#VRML V2.0 utf8\n";
?>

Shape {
   geometry Box {
   
<?php
   echo "      size $size $size $size \n";
?>

   }
}

you would end up with a 2x2x2 box again. The only difference is that $size is passed as part of the URL. Of course, you can't do HTTP POSTs with VRML, as there's no analogue of the HTML form, but there's nothing to stop you creating these kind of URLs manually and attaching them to Anchor nodes, or using Scripts to create them from values passed as events.

Anyway, now you know all you need. I'm going to finish off with an example that uses PHP to create a random ElevationGrid from parameters passed in the URL. Notice that because everything is generated from the URL parameters, so that you can generate many grids from the one file by changing the URL, shown in the links below:

• php-vrml.php?xdim=10&zdim=10&xspc=1&zspc=1
• php-vrml.php?xdim=10&zdim=20&xspc=0.1&zspc=0.1
• php-vrml.php?xdim=5&zdim=20&xspc=1&zspc=1
• php-vrml.php?xdim=20&zdim=20&xspc=1&zspc=1

Take a look at PHP code used to generate the results. The $xdim, $zdim, $zspc and $zspc variables are taken automatically from the URL parameters and used to create and position the grid appropriately. The heightfield is generated using one of PHPs built-in random number generators - if you reload the 3D file, you'll see that the grid changes each time. The heights are used twice, once for the heights themselves, and once for the colours of the points.

To give you an idea of how flexible the combination of PHP and VRML can be, take a look at the library section of this site. The whole thing is generated from PHP, using a MySQL database which holds the individual entries. Each entry is divided into 3 possible sections - a PROTO, an EXTERNPROTO, and the sample code. These three sections are combined inside PHP to create the various previews and code listings. One single PHP file deals with all the uses of the VRML. Firstly, it can create a sample file, which contains the EXTERNPROTO definition and the sample code. The EXTERNPROTO references the same PHP file with different URL arguments for the PROTO definitaion. Finally, both of these files can be downloaded to the client's machine, by setting the MIME type to application/octet-stream. The code listings are also created by generating the same VRML code and running it through a PHP syntax-highlighting function, then printing them as HTML. The techniques for using the database with PHP/VRML is just the same as for normal PHP.

There are many good PHP tutorials out there - php.net is probably a good place to start. Good luck!