more lua-script updates:

* comments and explain amp4.lua
* move amp1-3 to "Example" category

scripts/amp1.lua

@@ -1,7 +1,7 @@
 ardour {
 	["type"]    = "dsp",
 	name        = "Simple Amp",
-	category    = "Amplifier",
+	category    = "Example",
 	license     = "MIT",
 	author      = "Robin Gareus",
 	email       = "robin@gareus.org",

scripts/amp2.lua

@@ -1,7 +1,7 @@
 ardour {
 	["type"]    = "dsp",
 	name        = "Simple Amp II",
-	category    = "Amplifier",
+	category    = "Example",
 	license     = "MIT",
 	author      = "Robin Gareus",
 	email       = "robin@gareus.org",

scripts/amp3.lua

@@ -1,7 +1,7 @@
 ardour {
 	["type"]    = "dsp",
 	name        = "Simple Amp III",
-	category    = "Amplifier",
+	category    = "Example",
 	license     = "MIT",
 	author      = "Robin Gareus",
 	email       = "robin@gareus.org",

scripts/amp4.lua

@@ -6,12 +6,13 @@ ardour {
 	author      = "Robin Gareus",
 	email       = "robin@gareus.org",
 	site        = "http://gareus.org",
-	description = [[ Versatile +/- 20dB multichannel amplifier]]
+	description = [[Versatile +/- 20dB multichannel amplifier]]
 }
 
 function dsp_ioconfig ()
 	return
 	{
+		-- -1, -1 = any number of channels as long as input and output count matches
 		{ audio_in = -1, audio_out = -1},
 	}
 end
@@ -25,7 +26,7 @@ function dsp_params ()
 end
 
 local lpf = 0.02 -- parameter low-pass filter time-constant
-local cur_gain = 0 -- current gain (dB)
+local cur_gain = 0 -- current smoothed gain (dB)
 
 -- called once when plugin is instantiated
 function dsp_init (rate)
@@ -40,22 +41,15 @@ function low_pass_filter_param (old, new, limit)
 	end
 end
 
--- use ardour's vectorized functions
---
--- This is as efficient as Ardour doing it itself in C++
--- Lua function overhead is negligible
---
--- this also exemplifies the /simpler/ way of delegating the
--- channel-mapping to ardour.
-
+-- the DSP callback function
+-- "ins" and "outs" are http://manual.ardour.org/lua-scripting/class_reference/#C:FloatArray
 function dsp_run (ins, outs, n_samples)
-	assert (#ins == #outs) -- ensure that we can run in-place (channel count matches)
 	local ctrl = CtrlPorts:array() -- get control port array (read/write)
-	local siz = n_samples
-	local off = 0
+	local siz = n_samples -- samples remaining to process
+	local off = 0 -- already processed samples
 	local changed = false
 
-	-- if the gain parameter was changed, process at most 64 samples at a time
+	-- if the gain parameter was changed, process at most 32 samples at a time
 	-- and interpolate gain until the current settings match the target values
 	if cur_gain ~= ctrl[1] then
 		changed = true
@@ -63,12 +57,14 @@ function dsp_run (ins, outs, n_samples)
 	end
 
 	while n_samples > 0 do
-		if siz > n_samples then siz = n_samples end
+		if siz > n_samples then siz = n_samples end -- process at most "remaining samples"
 		if changed then
-			cur_gain = low_pass_filter_param (cur_gain, ctrl[1], 0.05)
+			-- smooth gain changes above 0.02 dB difference
+			cur_gain = low_pass_filter_param (cur_gain, ctrl[1], 0.02)
 		end
 
 		local gain = ARDOUR.DSP.dB_to_coefficient (cur_gain) -- 10 ^ (0.05 * cur_gain)
+
 		for c = 1,#ins do -- process all channels
 			-- check if output and input buffers for this channel are identical
 			-- http://manual.ardour.org/lua-scripting/class_reference/#C:FloatArray
@@ -76,7 +72,7 @@ function dsp_run (ins, outs, n_samples)
 				-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP
 				ARDOUR.DSP.copy_vector (outs[c]:offset (off), ins[c]:offset (off), siz)
 			end
-			ARDOUR.DSP.apply_gain_to_buffer (outs[c]:offset (off), siz, gain); -- process in-place
+			ARDOUR.DSP.apply_gain_to_buffer (outs[c]:offset (off), siz, gain); -- apply-gain, process in-place
 		end
 		n_samples = n_samples - siz
 		off = off + siz
@@ -90,18 +86,21 @@ end
 -------------------------------------------------------------------------------
 --- inline display + text example
 
-local txt = nil -- cache globally
+local txt = nil -- cache pango context globally
+
 function render_inline (ctx, w, max_h)
-	local ctrl = CtrlPorts:array ()
+	local ctrl = CtrlPorts:array () -- get control ports
 
 	if not txt then
+		-- allocate PangoLayout and set font
+		--http://manual.ardour.org/lua-scripting/class_reference/#Cairo:PangoLayout
 		txt = Cairo.PangoLayout (ctx, "Mono 8px")
 	end
 
 	txt:set_text (string.format ("%+.2f dB", ctrl[1]));
 	tw, th = txt:get_pixel_size ()
 
-	local h = math.ceil (th + 4) -- use text-height with 4px padding
+	local h = th + 4 -- use text-height with 4px padding
 	if (h > max_h) then h = max_h end -- but at most max-height
 
 	-- clear background
@@ -111,7 +110,7 @@ function render_inline (ctx, w, max_h)
 
 	-- center text
 	ctx:set_source_rgba (.8, .8, .8, 1.0)
-	ctx:move_to ( .5 * (w - tw), .5 * (h - th))
+	ctx:move_to (.5 * (w - tw), .5 * (h - th))
 	txt:show_in_cairo_context (ctx)
 
 	return {w, h}