[ardour-dev] logic to consider

[Paul Davis]

This is the actual code, in its almost pseudo-code-like simplicity,
that i am currently using to decide if we can configure a plugin
insert to match a given set of inputs+outputs. A -1 value for either
input or output counts means that we don't care about that
setting. the 3rd boolean argument to the function means that we
require an *exact* match on the number of inputs.

the "set_count()" function multiplies the (hidden) instances of the
plugin to get the required i/o counts.

If anyone has the time and inclination to review this, i'd appreciate
it. I've tried to comment it a bit more liberally than is my habit :)


int
PluginInsert::require_io (int32_t in, int32_t out, bool hard_input_limit)
{
	int32_t outputs = _plugins[0]->get_info().n_outputs;
	int32_t inputs = _plugins[0]->get_info().n_inputs;

	if (in == 0 || out == 0) {
		warning << _("programming error: ")
			<< X_("PluginInsert::require_io() called with inputs/outputs = zero!")
			<< endmsg;
		return -1; 
	}

	if (outputs == 0) {
		warning << compose (_("plugin %1 has no outputs. It cannot be used as an insert."),
				    _plugins[0]->name())
			<< endmsg;
		return -1;
	}

	if (inputs == 0) {

		/* instrument plugin, always legal, but it throws
		   away any existing active streams.

		   we do not multiply instrument plugins
		   to match in/out counts. if one instance
		   doesn't match the required outputs,
		   we fail.
		*/

		if (out != outputs) {
			return -1;
		}

		return set_count (1);
	}

	if (out == -1) {

		/* we don't care about outputs */

		if (in == -1) {
			/* we just don't care */
			return set_count (1);
		}

		/* we care about the input set up */

		if (hard_input_limit) {

			/* the number of inputs requested must 
			   be an exact multiple of natural plugin inputs.
			*/
			
			if ((in % inputs) != 0) {
				return -1;
			}

			/*
			   examples:

			   in = 1, plugin = 1in, cnt = 1
			   in = 1, plugin = 2in, rejected by mod test
			   in = 2, plugin = 1in, cnt = 2
			   in = 2, plugin = 2in, cnt = 1
			   in = 2, plugin = 4in, rejected by mod test
			   in = 3, plugin = 2in, rejected by mod test
			   in = 4, plugin = 2in, cnt = 2
			*/

			return set_count (in/inputs);

		} else {

			/* natural plugin inputs must be >= than the
			   number of inputs requested.
			*/

			if (inputs < in) {
				return -1;
			}

			/* we will use whatever input setup the plugin
			   has.
			*/

			/* use at least one plugin, or more if we
			   need more.
			   
			   examples:

			   in = 1, plugin = 1in, cnt = 1
			   in = 1, plugin = 2in, cnt = 1
			   in = 2, plugin = 1in, cnt = 2
			   in = 2, plugin = 2in, cnt = 1
			   in = 2, plugin = 4in, cnt = 1
			   in = 3, plugin = 2in, cnt = ceil (3/2) = 2
			   in = 4, plugin = 2in, cnt = 2
			*/

			if (inputs > in) {
				return set_count (1);
			} else {
				return set_count ((int32_t) ceil ((float)in/inputs));
			}
		}
	}

	if (in == -1) {

		/* we don't care about inputs */

		if (out == -1) {
			/* we just don't care */
			return set_count (1);
		}

		/* we care about the output set up */

		/* the number of outputs requested must 
		   be an exact multiple of natural plugin outputs.
		*/
		
		if ((out % outputs) != 0) {
			return -1;
		}

		return set_count (out/outputs);
	}

	/* we care about both input and output */

	/* require that the ratio of in/out requested matches
	   the ratio of the natural plugin in/out.
	*/

	if (((float)in/out) != ((float)inputs/outputs)) {
		return -1;
	}

	/* requested inputs+outputs must be exact multiples of
	   natural plugin in/out.
	*/
	
	if (in % inputs != 0 || out % outputs != 0) {
		return -1;
	}

	/* from here on we know that any adjustment
	   based on inputs will have the same effect
	   on outputs.
	*/

	if (inputs > in) {
		
		/* examples:
		   
		in = 1, plugin = 2in, cnt = 1
		   in = 2, plugin = 3in, cnt = 1
		*/

		set_count (1);

	} else {

		/* examples:
		   
		   in = 1, plugin = 1in, cnt = 1
		   in = 2, plugin = 2in, cnt = 1
		   in = 2, plugin = 1in, cnt = 2
		   in = 3, plugin = 1in, cnt = 3
		   in = 3, plugin = 2in, cnt = rejected by mod test
		*/

		set_count ((int32_t) ceil ((float)in / inputs));
	}

	return 0;
}