Add a Lua script snippet processing region data from the editor

scripts/s_region_gain.lua

@@ -0,0 +1,81 @@
+ardour { ["type"] = "Snippet", name = "Set Region Gain" }
+
+function factory () return function ()
+	-- get Editor GUI Selection
+	-- http://manual.ardour.org/lua-scripting/class_reference/#ArdourUI:Selection
+	local sel = Editor:get_selection ()
+
+	-- allocate a buffer (float* in C)
+	-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP:DspShm
+	local cmem = ARDOUR.DSP.DspShm (8192)
+
+	-- prepare undo operation
+	Session:begin_reversible_command ("Lua Region Gain")
+	local add_undo = false -- keep track if something has changed
+
+	-- iterate over selected regions
+	-- http://manual.ardour.org/lua-scripting/class_reference/#ArdourUI:RegionSelection
+	for r in sel.regions:regionlist ():iter () do
+		-- test if it's an audio region
+		if r:to_audioregion ():isnil () then
+			goto next
+		end
+
+		-- to read the Region data, we use the Readable interface of the Region
+		-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:Readable
+		local rd = r:to_readable ()
+
+		local n_samples = rd:readable_length ()
+		local n_channels = rd:n_channels ()
+
+		local peak = 0 -- the audio peak to be calculated
+
+		-- iterate over all channels in Audio Region
+		for c = 0, n_channels do
+			repeat
+				local pos = 0
+				-- read at most 8K samples of channel 'c'
+				local s = rd:read (cmem:to_float (0), pos, 8192, c)
+				pos = pos + s
+				-- access the raw audio data
+				-- http://manual.ardour.org/lua-scripting/class_reference/#C:FloatArray
+				local d = cmem:to_float (0):array()
+				-- iterate over the audio sample data
+				for i = 0, s do
+					if math.abs (d[i]) > peak then
+						peak = math.abs (d[i])
+					end
+				end
+			until pos < n_samples
+		end
+
+		if (peak > 0) then
+			print ("Region:", r:name (), "peak:", 20 * math.log (peak) / math.log(10), "dBFS")
+		else
+			print ("Region:", r:name (), " is silent")
+		end
+
+		-- normalize region
+		if (peak > 0) then
+			-- prepare for undo
+			r:to_stateful ():clear_changes ()
+			-- apply gain
+			r:to_audioregion (): set_scale_amplitude (1 / peak)
+			-- save changes (if any) to undo command
+			if not Session:add_stateful_diff_command (r:to_statefuldestructible ()):empty () then
+				add_undo = true
+			end
+		end
+
+		::next::
+	end
+
+	-- all done. now commit the combined undo operation
+	if add_undo then
+		-- the 'nil' command here means to use all collected diffs
+		Session:commit_reversible_command (nil)
+	else
+		Session:abort_reversible_command ()
+	end
+
+end end