The Generic Describe Action

	#include "ofxCore.h"
	#define kOfxActionDescribe "OfxActionDescribe" 

  • handle handle to the plug-in descriptor, cast to an OfxImageEffectHandle
  • inArgs is redundant and is set to NULL,
  • outArgs is redundant and is set to NULL.


The kOfxActionDescribe is the second action passed to a plug-in. It is where a plugin defines how it behaves and the resources it needs to function.

Note that the handle passed in acts as a descriptor for, rather than an instance of the plugin. The handle is global and unique. The plug-in is at liberty to cache the handle away for future reference until the plug-in is unloaded.

Most importantly, the effect must set what image effect contexts it is capable of working in.

This action must be trapped, it is not optional.


kOfxActionLoad has been called


  • kOfxActionDescribe will not be called again, unless it fails and returns one of the error codes where the host is allowed to attempt the action again
  • the handle argument, being the global plug-in description handle, is a valid handle from the end of a sucessful describe action until the end of the kOfxActionUnload action (ie: the plug-in can cache it away without worrying about it changing between actions).
  • kOfxImageEffectActionDescribeInContext will be called once for each context that the host and plug-in mutually support.

Return Values

  • kOfxStatOK, the action was trapped and all was well
  • kOfxStatErrMissingHostFeature, in which the plugin will be unloaded and ignored, plugin may post message
  • kOfxStatErrMemory, in which case describe may be called again after a memory purge
  • kOfxStatFailed, something wrong, but no error code appropriate, plugin to post message
  • kOfxStatErrFatal