The Describe In Context Action

	#include "ofxImageEffect.h"
	#define kOfxImageEffectActionDescribeInContext  "OfxImageEffectActionDescribeInContext"

  • handle handle to the context descriptor, cast to an OfxImageEffectHandle , this may or may not be the same as passed to kOfxActionDescribe .
  • inArgs has the following property...
  • outArgs is redundant and is set to NULL.


This action is unique to OFX Image Effect plug-ins. Because a plugin is able to exhibit different behaviour depending on the context of use, each separate context will need to be described individually. It is within this action that image effects describe which parameters and input clips it requires.

This action will be called multiple times, one for each of the contexts the plugin says it is capable of implementing. If a host does not support a certain context, then it need not call kOfxImageEffectActionDescribeInContext for that context.

This action must be trapped, it is not optional.


  • kOfxActionDescribe has been called on the descriptor handle,
  • kOfxActionCreateInstance has not been called,

Return Values

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