prototype lua midi generators & filters and port event-rewrite

scripts/midifilter.lua

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+ardour {
+	["type"]    = "dsp",
+	name        = "Midi Filter",
+	category    = "Utility",
+	license     = "MIT",
+	author      = "Robin Gareus",
+	email       = "robin@gareus.org",
+	site        = "http://gareus.org",
+	description = [[An Example Midi Filter for prototyping.]]
+}
+
+function dsp_ioconfig ()
+	return { { audio_in = 0, audio_out = 0}, }
+end
+
+function dsp_has_midi_input () return true end
+function dsp_has_midi_output () return true end
+
+function dsp_run (_, _, n_samples)
+	assert (type(midiin) == "table")
+	assert (type(midiout) == "table")
+	local cnt = 1;
+
+	function tx_midi (time, data)
+		midiout[cnt] = {}
+		midiout[cnt]["time"] = time;
+		midiout[cnt]["data"] = data;
+		cnt = cnt + 1;
+	end
+
+	-- for each incoming midi event
+	for _,b in pairs (midiin) do
+		local t = b["time"] -- t = [ 1 .. n_samples ]
+		local d = b["data"] -- get midi-event
+
+		if (#d == 3 and bit32.band (d[1], 240) == 144) then -- note on
+			tx_midi (t, d)
+		end
+		if (#d == 3 and bit32.band (d[1], 240) == 128) then -- note off
+			tx_midi (t, d)
+		end
+	end
+end