Example Lua script for inter-plugin communication

scripts/_dsp_plugin_communication.lua

@@ -0,0 +1,71 @@
+ardour { ["type"] = "dsp", name = "DSP Plugin Communication" }
+function dsp_ioconfig () return { { audio_in = -1, audio_out = -1} } end
+
+function dsp_init (rate)
+	self:shmem ():allocate (1)
+end
+
+function dsp_configure (ins, outs)
+end
+
+function dsp_params ()
+	return
+	{
+		{ ["type"] = "output", name = "self", min = 0, max = 8},
+		{ ["type"] = "output", name = "gain", min = 0, max = 2},
+	}
+end
+
+function dsp_run (ins, outs, n_samples)
+	local ctrl = CtrlPorts:array ()
+	local route = self:route ()
+	local shmem = self:shmem ()
+
+	local i = 0;
+	local l = 0;
+	local s = -1;
+
+	-- iterate overall plugins on this track,
+	-- find all LuaProc instances of this plugin (unique_id),
+	repeat
+		local proc = route:nth_plugin (i)
+		if not proc:isnil ()
+			and not proc:to_insert():plugin (0):to_luaproc():isnil ()
+			and proc:to_insert():plugin (0):unique_id () == self:unique_id () then
+			if (self:id ():to_s() == proc:to_insert():plugin (0):id ():to_s()) then
+				s = l; -- this plugin instance
+			end
+			if l == 0 then
+				shmem = proc:to_insert():plugin (0):to_luaproc():shmem ()
+			end
+			l = l + 1 -- count total instances of this plugin
+		end
+		i = i + 1
+	until proc:isnil ()
+
+	assert (s >= 0)
+	ctrl[1] = s;
+
+	-- calculate digital peak of all channels
+	local peak = 0
+	for c = 1,#ins do
+		if not ins[c]:sameinstance (outs[c]) then
+			ARDOUR.DSP.copy_vector (outs[c], ins[c], n_samples)
+		end
+		peak = ARDOUR.DSP.compute_peak(outs[c], n_samples, peak)
+	end
+
+	local a = shmem:to_float (0):array ()
+	if s == 0 then
+		-- the first plugin saves the peak
+		a[0] = peak
+		ctrl[2] = -1
+	else
+		-- all later plugins display the difference to the first.
+		if (a[0] == 0) then
+			ctrl[2] = 1
+		else
+			ctrl[2] = peak / a[0]
+		end
+	end
+end