OfxImageEffectSuiteV1 *gEffectSuite = 0;
OfxPropertySuiteV1    *gPropertySuite = 0;

////////////////////////////////////////////////////////////////////////////////
// Called at load
static OfxStatus
onLoad(void)
{
    // fetch the host suites out of the global host pointer
    if(!gHost) return kOfxStatErrMissingHostFeature;
    
    gEffectSuite     = (OfxImageEffectSuiteV1 *) gHost->fetchSuite(gHost->host, kOfxImageEffectSuite, 1);
    gPropertySuite   = (OfxPropertySuiteV1 *)    gHost->fetchSuite(gHost->host, kOfxPropertySuite, 1);
    if(!gEffectSuite || !gPropertySuite)
        return kOfxStatErrMissingHostFeature;
    return kOfxStatOK;
}

The load action is always the first action called after the initial boot-strap phase has happened. By this time the plug-in's setHost function will have been called, so we have access to the host pointer and so the ability to fetch suites.

What this action does is first to check that the host application has in fact set the gHost pointer, it then goes ahead and fetches two suites from the host. These suites are simply structs full of function pointers from the host which the plug-in uses to communicate with the host. We are only fetching two suites from the host, the OfxImageEffectSuiteV1 to give us access to images and more, and the OfxPropertySuiteV1 which allows us to access values in property sets.