update and cleanup lua example scripts

scripts/s_plugin_automation.lua

@@ -1,25 +1,33 @@
-ardour { ["type"] = "Snippet", name = "plugin automation2" }
+ardour { ["type"] = "Snippet", name = "Plugin automation" }
 
 function factory () return function ()
+	-- query playhead position and session sample-rate
 	local playhead = Session:transport_frame ()
 	local samplerate = Session:nominal_frame_rate ()
 
+	-- get Track/Bus with RID 3
 	local r = Session:route_by_remote_id(3)
-	-- get AutomationControList, ControlList and ParameterDescriptor
-	local acl, cl, pd = ARDOUR.LuaAPI.plugin_automation (r:nth_plugin (0), 0)
+	-- make sure the track object exists
+	assert (not r:isnil ())
 
-	if not acl:isnil() then
+	-- get AutomationList, ControlList and ParameterDescriptor
+	-- of the first plugin's first parameter
+	-- see http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:LuaAPI
+	local al, cl, pd = ARDOUR.LuaAPI.plugin_automation (r:nth_plugin (0), 0)
+
+	if not al:isnil () then
 		print ("Parameter Range", pd.lower, pd.upper)
-		print ("Current value", cl:eval(playhead))
+		print ("Current value", cl:eval (playhead))
 
 		-- prepare undo operation
 		Session:begin_reversible_command ("Automatix")
-		local before = acl:get_state()
+		-- remember current AutomationList state
+		local before = al:get_state()
 
 		-- remove future automation
 		cl:truncate_end (playhead)
 
-		-- add new data points after the playhead 1 sec min..max
+		-- add new data points after the playhead 1 sec, min..max
 		-- without guard-points, but with initial (..., false, true)
 		for i=0,10 do
 			cl:add (playhead + i * samplerate / 10,
@@ -28,8 +36,8 @@ function factory () return function ()
 		end
 
 		-- save undo
-		local after = acl:get_state()
-		Session:add_command (acl:memento_command(before, after))
+		local after = al:get_state()
+		Session:add_command (al:memento_command(before, after))
 		Session:commit_reversible_command (nil)
 	end
 end end