// forward declaration of two functions needed by the plug-in struct
static OfxStatus pluginMain(const char *action,  const void *handle, OfxPropertySetHandle inArgs,  OfxPropertySetHandle outArgs);
static void setHostFunc(OfxHost *hostStruct);

////////////////////////////////////////////////////////////////////////////////
// the plugin struct 
static OfxPlugin pluginStruct = 
{       
  kOfxImageEffectPluginApi,
  1,
  "net.sf.openfx.OfxInvertExample",
  1,
  0,
  setHostFunc,
  pluginMain
};
   
// the mandated function to return the nth plug-in
OfxExport OfxPlugin *
OfxGetPlugin(int nth)
{
  if(nth == 0)
    return &pluginStruct;
  return 0;
}
 
// the mandated function to return the number of plug-ins in this binary
OfxExport int
OfxGetNumberOfPlugins(void)
{       
  return 1;
}

The first thing to note in this section are the two functions OfxGetPlugin and OfxGetNumberOfPlugins . These two functions are the only symbols that a plug-in must export and are there to boot strap the whole plug-in identification and definition process. Note the macro OfxExport , which should be inserted before any symbol that needs to be exported from the plug-in.

OfxGetNumberOfPlugins is the first function by a host after a binary is loaded. It returns the number of separate plug-ins contained inside the binary. In this case we have only one plug-in.

OfxGetPlugin is called once for each plug-in inside the binary, and returns an OfxPlugin struct. This struct is used to tell the host what kind of plug-in it is, it's name, versioning info and to give the host two functions to use for communications. Our function returns a pointer to the static pluginStruct . All such structs should be static to avoid memory allocation issues, otherwise they will not be deleted by the host.

In order the members of pluginStruct tell the host...