I have mentioned all that in many posts, but here is a short explanation at one place.
Hardware Control Surfaces can send (some of them also receive) MIDI events. These events when used for Control Surface purpose are normally completely unrelated to what they do with SONAR. Note C4 can switch Mute on one track and PitchBend can control volume of another. But also PitchBend can control Mute and C4 volume. So, it does not really matter what Control Surface can send, what matters is that it sends something. For example, if it does not send anything when you "Touch" your fader SONAR can not detect the touch. But in case it send something (Note, CC, Program change, SysEx, etc.), SONAR can use the fact independent from concrete format of the message.
SONAR Control Surface API. While SONAR can interpret MIDI messages directly, as MIDI input for track and "Remote control" of some parameters, that is NOT what is called Control Surface approach. SONAR has special Application Programming Interface (API). Unlike User Interface (UI) which you percept as SONAR and can control with keys and mouse, API can be controlled from special program ONLY. It has absolutely no relations to some MIDI inputs. That API in general allows:
- Get some information from SONAR (current context, track names, VST parameter values, current time, etc)
- Execute some command (start play, show inspector, focus track, etc)
- Change some parameters (volumes, VST, etc)
SONAR Control Surface Plug-in is a program which react on input from your Hardware Control Surface (normally MIDI, but can be something unrelated from the Network for example) and ask Control Surface API for something. The mapping is in general arbitrary and it is defined by that program logic. Generic Surface plug-in maps one MIDI message to one parameter change or command. ACT MIDI plug-in maps it dynamically and partially configurable to some parameters/commands with dependency on some internal (in this plug-in) states (like ACT/non ACT mode, single/multi strips, "Shift", etc). Mack.. and VS plug-ins have quite complicated fixed logic for the mapping. AZ Controller plug-in has arbitrary user definable logic. But all of them:
- Detect some input from hardware
- Decide what that input should do according to the programmed logic
- Call SONAR throw CS API to do that
