The header files used to define the OFX Image Effect API are...
ofxCore.h- provides the core definitions of the general OFX architecture that allow the bootstrapping of specific APIs, as well as several core actions,
ofxProperty.h- provides generic property fetching suite used to get and set values about objects in the API,
ofxParam.h- provides the suite for defining user visible parameters to an effect,
ofxMultiThread.h- provides the suite for basic multi-threading capabilities,
ofxInteract.h- provides the suite that allows a plug-in to use OpenGL to draw their own interactive GUI tools,
ofxKeySyms.h- provides key symbols used by 'Interacts' to represent keyboard events,
ofxMemory.h- provides a simple memory allocation suite,
ofxMessage.h- provides a simple messaging suite to communicate with an end user,
ofxImageEffect.h- defines a suite and set of actions that draws all the above together to create an visual effect plug-in.
These contain the suite definitions, property definitions and action definitions that are used by the API.