I hooked a function into Tracker.Visit.isExcluded. When I try to use Piwik_API_Request to get a value from my api function I get that fatal error. Tracker debug is enabled.
_Fatal error: Class 'Piwik_ApiProxy' not found in piwik/core/API/Request.php on line 113
I don't have to use the api call, but it would be cleaner (although less performant?), so I set the prio to normal.
Please also tell me if I should use the api call instead of duplicating a few lines of code. I'm not sure because the tracker probably is performance critical.
Please use the piwik-hackers mailing list for dev questions.
Not having seen your code, it should be possible to use Piwik_API_Request from within a plugin.
BTW if you want the data in native PHP form, use serialize=0 in your parameter list.