int error = BeginDoubleBuffer(APTR handle, struct hwTagList *tags);
Please note that this function will only be called if the Hollywood script explicitly requests
a hardware double buffer, i.e. the user has to set the hardware parameter to
True when he calls
BeginDoubleBuffer() function. If he doesn't do that, Hollywood will use its own
software double buffering method and your plugin's
BeginDoubleBuffer() function will never be
called at all.
BeginDoubleBuffer() is an optional API and must only be implemented if
has been passed to hw_SetDisplayAdapter(). See hw_SetDisplayAdapter for details.