How to change __autoload to spl_autoload_register using array?

Question

I know there’s a lot of websites about it. But I confess that I searched and did not understand.

The point is that this site is old and was on a server needed to change it to newer version of PHP.

And I came across this mistake:

Deprecated: __autoload() is deprecated, use spl_autoload_register() instead 

I know it’s about __autoload being obsolete, but I’m not getting the basics of adding spl_autoload_register into this call.

<?php
function __autoload($className) {
    $classpath = array(
        'model/','helpers/','lib/','plugin/email/',//frontend
        '../model/','../helpers/','../plugin/email/'//backend
        );    
    $classFile = ucfirst($className) . ".php";
    $loaded = false;
    foreach ($classpath as $path) {
        if (is_readable("$path$classFile")) {
            require "$path$classFile";
            $loaded = true;
            break;
        }
    }
}
?>

I tried to do so:

 <?php
    function autoload_1($className) {
        $classpath = array(
            'model/','helpers/','lib/','plugin/email/',//frontend
            '../model/','../helpers/','../plugin/email/'//backend
            );    
        $classFile = ucfirst($className) . ".php";
        $loaded = false;
        foreach ($classpath as $path) {
            if (is_readable("$path$classFile")) {
                require "$path$classFile";
                $loaded = true;
                break;
            }
        }
    }
spl_autoload_register('autoload_1');

But this returning blank page without error, that’s where I got lost.

Someone could help or guide me to the solution.

Thank you.