The callgrind writer is implemented in the lib/callgrindWriter.php file. It exposes one function:

function ​​​​​​​web3tracer_callgrindWrite($data,$filename=null,$path=null)

Writes the profile data in callgrind format, suitable to read with KCachegrind.

Parameters:

$data - is the data returned by the web3tracer_disable() function

$filename - is the name of the file to be written. If null, a name is automatically generated in the form callgrind.2013-05-24-12-59-03

$path - Directory in which to write the file. If null, current directory is used.

Returns:

true on success, false on failure (file is not writable)