Prototype an A/B x-fade plugin

share/scripts/_ab_switch.lua

@@ -0,0 +1,96 @@
+ardour {
+	["type"]    = "dsp",
+	name        = "a-b Switch",
+	category    = "Amplifier",
+	license     = "MIT",
+	author      = "Ardour Team",
+	description = [[Auotomatable A/B Input Select. Channels are mapped in pairs: In 1/2 -> Out 1, In 3/4 -> Out 2, etc.]]
+}
+
+function dsp_ioconfig ()
+	return {
+		-- in theory any combination with N_in = 2 * N_out is possible
+		-- (and we should inform the host to override strict-i/o
+		-- connect_all_audio_outputs = true)
+		{ audio_in = 2, audio_out = 1},
+		{ audio_in = 4, audio_out = 2},
+		{ audio_in = 8, audio_out = 4},
+	}
+end
+
+function dsp_params ()
+	return { { ["type"] = "input", name = "A/B", min = 0, max = 1, default = 0, toggled = true } }
+end
+
+local sr = 48000
+local cur_a = 0.0
+local cur_b = 0.0
+
+function dsp_init (rate)
+	sr = rate
+end
+
+function dsp_configure (ins, outs)
+	n_ainp = ins:n_audio ()
+	n_aout = outs:n_audio ()
+	assert (n_aout * 2 == n_ainp)
+end
+
+-- the DSP callback function
+function dsp_runmap (bufs, in_map, out_map, n_samples, offset)
+	local ctrl = CtrlPorts:array() -- get control port array
+	local target_A = ctrl[1] > 0 and 0.0 or 1.0
+	local target_B = 1 - target_A
+
+	local gA = cur_a
+	local gB = cur_b
+
+	for c = 1, n_aout do
+		local o = out_map:get (ARDOUR.DataType ("audio"), c - 1)
+		if o == ARDOUR.ChanMapping.Invalid then
+			goto next
+		end
+
+		local in_a = c * 2 - 1
+		local in_b = c * 2
+		local ia = in_map:get (ARDOUR.DataType ("audio"), in_a - 1)
+		local ib = in_map:get (ARDOUR.DataType ("audio"), in_b - 1)
+
+		local buf_aout = bufs:get_audio(o)
+
+		-- optimize fixed gain case
+		if cur_a == target_A and cur_b == target_B then
+			if target_A == 1.0 then
+				-- the first (and only first) channel may be in-place
+				if buf_aout ~= bufs:get_audio(ia) then
+					buf_aout:read_from (bufs:get_audio(ia):data (0), n_samples, offset, offset)
+				end
+			else
+				assert (buf_aout ~= bufs:get_audio(ib))
+				buf_aout:read_from (bufs:get_audio(ib):data (0), n_samples, offset, offset)
+			end
+			goto next
+		end
+
+		-- apply gain to each input channel
+		if ia ~= ARDOUR.ChanMapping.Invalid and ia ~= ib then
+			cur_a = ARDOUR.Amp.apply_gain (bufs:get_audio(ia), sr, n_samples, gA, target_A, offset)
+		end
+		if ib ~= ARDOUR.ChanMapping.Invalid and ia ~= ib then
+			cur_b = ARDOUR.Amp.apply_gain (bufs:get_audio(ib), sr, n_samples, gB, target_B, offset)
+		end
+
+		-- channels are supposed to be in linear order
+		assert (buf_aout ~= bufs:get_audio(ib))
+
+		-- copy input to output if needed (first channel may be in-place)
+		if buf_aout ~= bufs:get_audio(ia) then
+			buf_aout:read_from (bufs:get_audio(ia):data (0), n_samples, offset, offset)
+		end
+
+		-- add the second buffer
+		ARDOUR.DSP.mix_buffers_no_gain (buf_aout:data (offset), bufs:get_audio(ib):data (offset), n_samples)
+
+		::next::
+	end
+end