Paired server side and client side classes are required for each animation object. The server side class should be derived from one of the abstract base classes, based on CAnim, depending on whether the animation is to draw to a sprite or a window:
CSpriteAnim for sprite animations
CWindowAnim for window animations
CFreeTimerWindowAnim for free timer animations
The derived classes are constructed in the DLL factory class CAnimDll::CreateInstanceL() function. See Creating an Animation Object.
CAnim defines the server side functions that are used to implement a given animation, including the drawing commands that the Window Server calls and any other command functions the animation may require. These functions must be implemented by the user in the derived class.
The MAnimGeneralFunctions, MAnimWindowFunctions and MAnimSpriteFunctions classes provide a set of helper functions that are implemented by the Window Server and to which CAnim provides the iFunctions pointer. These helper functions, which include for example functions to set the animation timings, to set the drawing rectangle, to panic the client from the server, and so on, are therefore available to any CAnim derived class.