PHP code to obfuscate HTML?

Not true obfuscation, but rather hard to read in most cases (and less bandwidth-intensive as well!)

<?php
ob_start();

// Generate output here

$output = ob_get_contents();
ob_end_clean();

$output = preg_replace('\s{2,}',' ', $output);
echo $output;
?>

You can compress your JavaScript and css

For php output it can be done using ob_start have a look at this http://ru.php.net/manual/en/function.ob-start.php#71953

You should have a look at Minify it has a Minify_HTML class removing whitespace, unnecessary comments and tokens

Well, in my studies of HTML obfuscator, like http://htmlobfuscator.com/, are truely change their "special" code into reversed base64. When we decode it, they're actually packed js file using packer that you could find on Google.

So, now we could do this
Slashup the whole html, for the Js string, then "pack" the javascript, then encode it into base64, then rotate the encoded string. Viola, done. You'll get something like this:

var IO1='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';function l1O(data){var OOOlOI="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";var o1,o2,o3,h1,h2,h3,h4,bits,i=0,enc='';do{h1=OOOlOI.indexOf(data.charAt(i++));h2=OOOlOI.indexOf(data.charAt(i++));h3=OOOlOI.indexOf(data.charAt(i++));h4=OOOlOI.indexOf(data.charAt(i++));bits=h1>16&0xff;o2=bits>>8&0xff;o3=bits&0xff;if(h3==64){enc+=String.fromCharCode(o1)}else if(h4==64){enc+=String.fromCharCode(o1,o2)}else{enc+=String.fromCharCode(o1,o2,o3)}}while(i= 0; i-- ){ ret += string.charAt(i);} return ret; }eval(l1O(OOO(IO1)));

Good luck~

No, php couldn't do that without something on the client side. You could always have some javascript decode it, but that wouldnt be friendly to whoever has it turned off, it would be slow and no search engine support.