osc: allow re-sending of same values

[OddBloke]

osc_set in osc.c doesn't send output on a channel if the value is unchanged:

midimonster/backends/osc.c

Lines 735 to 746 in 1f31bc7

	//only output on change
	current = osc_parameter_denormalise(data->channel[ident.fields.channel].type[ident.fields.parameter],
	data->channel[ident.fields.channel].min[ident.fields.parameter],
	data->channel[ident.fields.channel].max[ident.fields.parameter],
	v[evt]);
	if(memcmp(&current, &data->channel[ident.fields.channel].out[ident.fields.parameter], sizeof(current))){
	//update current value
	data->channel[ident.fields.channel].out[ident.fields.parameter] = current;
	//mark channel
	data->channel[ident.fields.channel].mark = 1;
	mark = 1;
	}

This is a problem when integrating with REAPER's OSC implementation: they define a t trigger type (from this mirror of their default config):

# t: trigger or toggle message. The device triggers the action, or toggles the
# state, when the pattern is sent with no arguments, or with an argument of 1.
# The feedback values REAPER sends are identical to those sent for binary 
# arguments.

So: I can send the first trigger with no problem, but any subsequent triggering "1" values are never sent by osc.c.

(The workaround, at least for REAPER, is to send a 0 value before sending the trigger value: REAPER ignores any value but "1", but doing so invalidates the "cached" value in osc.c. It would be good to be able to avoid the extra messages over the wire.)

[cbdevnet]

Hi @OddBloke, thanks for this well-researched issue! Unfortunately it seems like Reaper is re-using the t OSC tag here, which is already defined by the OSC specification as time-tag - otherwise a solution might have been to simply implement these additional tags.

I'll need to think about a way to indicate that the event-deduplication should be disabled for specific OSC paths. I would not like to disable the deduplication globally, as that would cause a lot of events to be output when translating from backends that might not do their own event deduplication.