[linux-audio-dev] XAP: magic 'sys controls' vs normal controls

[Tim Hockin]

> (Speaking of which, I implemented a VVID manager for Audiality the 
> other day. "Finished and tested", although I haven't integrated it 
> yet.)

excellent - and the code is where? :)

> > * This is all designed to take away the extra fields that aren't
> 
> How many fields can actually be eliminated? Can't be many bytes, and 
> there aren't all that many of these controls. I can't see that it's 
> worth any special casing to save a few fields per "magic control".

not many I realized - how does the below code look?

> There should be no special "MIDI compatible" controls at all, IMHO, 

Well, we want MIDI compatible hinted controls to fall withing the -1 to 1 or
0-1 range, right?  That is a bit more than a hint..

> in the way suggested by the Control hint names. We could have an 
> official MIDI CC -> Control mapping, if desired, but no actual 
> references to MIDI in the API.

Well, we're documenting things as MIDI-compatible hints, right?  I.e.: use
this hint if you want a host to know it should connect MIDI velocity.

> Well, I still think the cleanest way would be to use the Control 
> metadata stuff, giving the timeline controls datatype IDs of their 


How's this look - like what you are thinking?



/*
 * System controls are base-typed controls - they receive specific data via
 * specific events.  Plugins can use these controls to receive special
 * messages from the host.
 */
#define XAP_DECL_CTRL_SYS(label, name, hints, flags, rtflags) { \
        .type = XAP_CTRL_SYS, \
        .label = label, \
        .name = name, \
        .hints = hints, \
        .flags = flags, \
        .rtflags = rtflags \
}

/*
 * TEMPO (double : ticks/sec)
 * - gets values [-inf, inf] via XAP_EV_TEMPO
 * - hosts must send a TEMPO event at plugin init and when tempo changes
 */
#define XAP_TEMPO_CTRL(label, name) \
    XAP_DECL_CTRL_SYS(label, name, XAP_CTRLHINT_TEMPO, 0, 0)

/*
 * METER (double : ticks/measure)
 * - gets values [1.0, inf] via XAP_EV_METER
 * - hosts must send a METER event at plugin init and when meter changes
 * - hosts should send a METER event periodically, such as every measure or
 *   once per second
 */
#define XAP_METER_CTRL(label, name) \
    XAP_DECL_CTRL_SYS(label, name, XAP_CTRLHINT_METER, 0, 0)


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