When a host upgrades an instance of a VST 2 plugin to its VST 3 equivalent there are defined mechanisms for upgrading the FXB data to the new instance.
What about parameters though? How should the host map stored VST 2 automation parameter indicies to the equivalent parameter ids for the new VST 3 plugin instance?
Hi,
the state persistence is described in the FAQ section in the documentation.
A plug-in has to set the VST3 parameter ID to the index of the VST2 parameter when updated to VST3. Otherwise automation is not compatible.