From 15f9fa724a94530b19516bf6a78109f7981192cc Mon Sep 17 00:00:00 2001
From: m1macrophage <168948267+m1macrophage@users.noreply.github.com>
Date: Fri, 28 Feb 2025 00:08:20 -0800
Subject: [PATCH] Multiple synth layouts: updated to the latest slider script.
 (#13422)

* Explicit configuration: Using add_* functions, instead of scanning through the layout for sliders.
* Separated the copy-pasteable portion of the script.
* A no-op for the DMX and LinnDrum layouts.
* Fixes multitouch and slider "drift", and adds support for relative adjustments to the D70 sliders (they were using an older version of the script).
---
 src/mame/layout/linn_linndrum.lay | 243 +++++++++++++++-------------
 src/mame/layout/oberheim_dmx.lay  | 253 ++++++++++++++++--------------
 src/mame/layout/roland_d70.lay    | 197 ++++++++++++++---------
 3 files changed, 394 insertions(+), 299 deletions(-)

diff --git a/src/mame/layout/linn_linndrum.lay b/src/mame/layout/linn_linndrum.lay
index 66530763c41..f755488d13f 100644
--- a/src/mame/layout/linn_linndrum.lay
+++ b/src/mame/layout/linn_linndrum.lay
@@ -594,121 +594,140 @@ copyright-holders:m1macrophage
 	<script><![CDATA[
 		file:set_resolve_tags_callback(
 			function()
-				local id_port_index <const> = string.len("slider_knob_") + 1
-
-				-- State used by pointer handlers.
-				local sliders = {}  -- Info about all sliders (constant after initialization).
-				local pointers = {}  -- Pointer tracking state.
-
-				-- Gather relevant elements and inputs into `sliders`.
 				local view = file.views["Default Layout"]
-				for i = 1, #view.items do
-					local item = view.items:at(i)
-					if item.id ~= nil and string.find(item.id, "slider_knob_") == 1 then
-						local slider_id = string.sub(item.id, id_port_index)
-
-						local port = file.device:ioport(slider_id)
-						local field = nil
-						if port ~= nil then
-							for k, val in pairs(port.fields) do
-								field = val
-								break
-							end
-							if field == nil then
-								print("LAYOUT ERROR - Port does not have a field: " .. slider_id)
-							end
-						else
-							print("LAYOUT ERROR - Port not found: " .. slider_id)
-						end
-
-						local slider = view.items["slider_" .. slider_id]
-						if slider == nil then
-							print("LAYOUT ERROR - Element: 'slider_" .. slider_id .. "' does not exist.")
-						end
-
-						local slider_info = {}
-						slider_info.slider = slider
-						slider_info.knob = item
-						slider_info.field = field
-						table.insert(sliders, slider_info)
-					end
+				install_slider_callbacks(view)
+				for i = 1, 16 do
+					local pan_input = "pot_pan_" .. i
+					add_vertical_slider(view, "slider_" .. pan_input, "slider_knob_" .. pan_input, pan_input)
+					local gain_input = "pot_gain_" .. i
+					add_vertical_slider(view, "slider_" .. gain_input, "slider_knob_" .. gain_input, gain_input)
 				end
-
-				local function forget_pointers()
-					pointers = {}
-				end
-
-				local function pointer_lost(type, id, dev, x, y, up, cnt)
-					pointers[id] = nil
-				end
-
-				local function pointer_updated(type, id, dev, x, y, btn, dn, up, cnt)
-					-- Button not pressed? Reset state of current pointer.
-					if btn & 1 == 0 then
-						pointers[id] = nil
-						return
-					end
-
-					-- Button just pressed? Find affected slider, if any.
-					if dn & 1 ~= 0 then
-						for i = 1, #sliders do
-							if sliders[i].knob.bounds:includes(x, y) then
-								local pointer = {}
-								pointer.selected_slider = i
-								pointer.relative = true
-								pointer.start_y = y
-								pointer.start_value = sliders[i].field.user_value
-								pointers[id] = pointer
-								break
-							elseif sliders[i].slider.bounds:includes(x, y) then
-								local pointer = {}
-								pointer.selected_slider = i
-								pointer.relative = false
-								pointers[id] = pointer
-								break
-							end
-						end
-					end
-
-					-- No slider selected by current pointer? Nothing to do.
-					if pointers[id] == nil then
-						return
-					end
-
-					-- A slider is selected. Update state and, indirectly,
-					-- slider knob position, based on the pointer's Y position.
-					-- It is assumed the attached IO field is an IPT_ADJUSTER
-					-- with a range of 0-100 (the default).
-
-					local pointer = pointers[id]
-					local slider_info = sliders[pointer.selected_slider]
-
-					local knob_half_height = slider_info.knob.bounds.height / 2
-					local min_y = slider_info.slider.bounds.y0 + knob_half_height
-					local max_y = slider_info.slider.bounds.y1 - knob_half_height
-
-					local new_value = 0
-					if pointer.relative then
-						-- User clicked on the knob. New value depends on how
-						-- much the knob was dragged.
-						new_value = pointer.start_value - 100 * (y - pointer.start_y) / (max_y - min_y)
-					else
-						-- User clicked elsewhere on the slider. New value
-						-- depends on the absolute position of the click.
-						new_value = 100 - 100 * (y - min_y) / (max_y - min_y)
-					end
-
-					new_value = math.floor(new_value + 0.5)
-					if new_value < 0 then new_value = 0 end
-					if new_value > 100 then new_value = 100 end
-					slider_info.field.user_value = new_value
-				end
-
-				view:set_pointer_updated_callback(pointer_updated)
-				view:set_pointer_left_callback(pointer_lost)
-				view:set_pointer_aborted_callback(pointer_lost)
-				view:set_forget_pointers_callback(forget_pointers)
 			end)
+
+		-----------------------------------------------------------------------
+		-- Slider library starts.
+		-- Can be copied as-is to other layouts.
+		-----------------------------------------------------------------------
+		local sliders = {}   -- Stores slider information.
+		local pointers = {}  -- Tracks pointer state.
+
+		-- The knob's Y position must be animated using <animate inputtag="{port_name}">.
+		-- The click area's vertical size must exactly span the range of the
+		-- knob's movement.
+		function add_vertical_slider(view, clickarea_id, knob_id, port_name)
+			local slider = {}
+
+			slider.clickarea = view.items[clickarea_id]
+			if slider.clickarea == nil then
+				emu.print_error("Slider element: '" .. clickarea_id .. "' not found.")
+				return
+			end
+
+			slider.knob = view.items[knob_id]
+			if slider.knob == nil then
+				emu.print_error("Slider knob element: '" .. knob_id .. "' not found.")
+				return
+			end
+
+			local port = file.device:ioport(port_name)
+			if port == nil then
+				emu.print_error("Port: '" .. port_name .. "' not found.")
+				return
+			end
+
+			slider.field = nil
+			for k, val in pairs(port.fields) do
+				slider.field = val
+				break
+			end
+			if slider.field == nil then
+				emu.print_error("Port: '" .. port_name .."' does not seem to be an IPT_ADJUSTER.")
+				return
+			end
+
+			table.insert(sliders, slider)
+		end
+
+		local function pointer_updated(type, id, dev, x, y, btn, dn, up, cnt)
+			-- If a button is not pressed, reset the state of the current pointer.
+			if btn & 1 == 0 then
+				pointers[id] = nil
+				return
+			end
+
+			-- If a button was just pressed, find the affected slider, if any.
+			if dn & 1 ~= 0 then
+				for i = 1, #sliders do
+					if sliders[i].knob.bounds:includes(x, y) then
+						pointers[id] = {
+							selected_slider = i,
+							relative = true,
+							start_y = y,
+							start_value = sliders[i].field.user_value }
+						break
+					elseif sliders[i].clickarea.bounds:includes(x, y) then
+						pointers[id] = {
+							selected_slider = i,
+							relative = false }
+						break
+					end
+				end
+			end
+
+			-- If there is no slider selected by the current pointer, we are done.
+			if pointers[id] == nil then
+				return
+			end
+
+			-- A slider is selected. Update state and, indirectly, slider knob position,
+			-- based on the pointer's Y position. It is assumed the attached IO field is
+			-- an IPT_ADJUSTER with a range of 0-100 (the default).
+
+			local pointer = pointers[id]
+			local slider = sliders[pointer.selected_slider]
+
+			local knob_half_height = slider.knob.bounds.height / 2
+			local min_y = slider.clickarea.bounds.y0 + knob_half_height
+			local max_y = slider.clickarea.bounds.y1 - knob_half_height
+
+			local new_value = 0
+			if pointer.relative then
+				-- User clicked on the knob. The new value will depend on how much the
+				-- knob was dragged.
+				new_value = pointer.start_value - 100 * (y - pointer.start_y) / (max_y - min_y)
+			else
+				-- User clicked elsewhere on the slider. The new value will depend on
+				-- the absolute position of the click.
+				new_value = 100 - 100 * (y - min_y) / (max_y - min_y)
+			end
+
+			new_value = math.floor(new_value + 0.5)
+			if new_value < 0 then new_value = 0 end
+			if new_value > 100 then new_value = 100 end
+			slider.field.user_value = new_value
+		end
+
+		local function pointer_left(type, id, dev, x, y, up, cnt)
+			pointers[id] = nil
+		end
+
+		local function pointer_aborted(type, id, dev, x, y, up, cnt)
+			pointers[id] = nil
+		end
+
+		local function forget_pointers()
+			pointers = {}
+		end
+
+		function install_slider_callbacks(view)
+			view:set_pointer_updated_callback(pointer_updated)
+			view:set_pointer_left_callback(pointer_left)
+			view:set_pointer_aborted_callback(pointer_aborted)
+			view:set_forget_pointers_callback(forget_pointers)
+		end
+		-----------------------------------------------------------------------
+		-- Slider library ends.
+		-----------------------------------------------------------------------
 	]]></script>
 </mamelayout>
 
diff --git a/src/mame/layout/oberheim_dmx.lay b/src/mame/layout/oberheim_dmx.lay
index f293000cc8d..d4a8aaeb4d9 100644
--- a/src/mame/layout/oberheim_dmx.lay
+++ b/src/mame/layout/oberheim_dmx.lay
@@ -92,13 +92,13 @@ copyright-holders:m1macrophage
 	</element>
 
 	<group name="trimmer">
-		<element ref="invisible-rect" id="slider_pitch_adj_~trimmer_id~">
+		<element ref="invisible-rect" id="trimmer_~trimmer_id~">
 			<bounds x="0" y="0" width="15" height="40"/>
 		</element>
 		<element ref="trimmer-rail">
 			<bounds x="5" y="0" width="5" height="40"/>
 		</element>
-		<element ref="trimmer-knob" id="slider_knob_pitch_adj_~trimmer_id~">
+		<element ref="trimmer-knob" id="trimmer_knob_~trimmer_id~">
 			<animate inputtag="pitch_adj_~trimmer_id~" inputmask="0x7f"/>
 			<bounds state="100" x="0" y="0" width="15" height="5"/>
 			<bounds state="0" x="0" y="35" width="15" height="5"/>
@@ -117,13 +117,13 @@ copyright-holders:m1macrophage
 	</element>
 
 	<group name="fader">
-		<element id="slider_fader_p~fader_id~" ref="invisible-rect">
+		<element id="fader_~fader_id~" ref="invisible-rect">
 			<bounds x="15" y="0" width="35" height="162"/>
 		</element>
 		<element ref="black-rect">  <!-- slider rail -->
 			<bounds x="29" y="9" width="7" height="144"/>
 		</element>
-		<element id="slider_knob_fader_p~fader_id~" ref="fader-knob">
+		<element id="fader_knob_~fader_id~" ref="fader-knob">
 			<animate inputtag="fader_p~fader_id~" inputmask="0x7f"/>
 			<bounds state="100" x="15" y="0" width="35" height="35"/>
 			<bounds state="0" x="15" y="127" width="35" height="35"/>
@@ -355,8 +355,8 @@ copyright-holders:m1macrophage
 			</element>
 		</repeat>
 
-		<!-- Tunning trimmers -->
-		<collection name="tunning">
+		<!-- Tuning trimmers -->
+		<collection name="tuning">
 			<element ref="text-tune">
 				<bounds x="20" y="110" width="30" height="10"/>
 			</element>
@@ -541,121 +541,144 @@ copyright-holders:m1macrophage
 	<script><![CDATA[
 		file:set_resolve_tags_callback(
 			function()
-				local id_port_index <const> = string.len("slider_knob_") + 1
-
-				-- State used by pointer handlers.
-				local sliders = {}  -- Info about all sliders (constant after initialization).
-				local pointers = {}  -- Pointer tracking state.
-
-				-- Gather relevant elements and inputs into `sliders`.
 				local view = file.views["Default Layout"]
-				for i = 1, #view.items do
-					local item = view.items:at(i)
-					if item.id ~= nil and string.find(item.id, "slider_knob_") == 1 then
-						local slider_id = string.sub(item.id, id_port_index)
+				install_slider_callbacks(view)
 
-						local port = file.device:ioport(slider_id)
-						local field = nil
-						if port ~= nil then
-							for k, val in pairs(port.fields) do
-								field = val
-								break
-							end
-							if field == nil then
-								print("LAYOUT ERROR - Port does not have a field: " .. slider_id)
-							end
-						else
-							print("LAYOUT ERROR - Port not found: " .. slider_id)
-						end
-
-						local slider = view.items["slider_" .. slider_id]
-						if slider == nil then
-							print("LAYOUT ERROR - Element: 'slider_" .. slider_id .. "' does not exist.")
-						end
-
-						local slider_info = {}
-						slider_info.slider = slider
-						slider_info.knob = item
-						slider_info.field = field
-						table.insert(sliders, slider_info)
-					end
+				-- Configure volume faders.
+				for i = 1, 10 do
+					add_vertical_slider(view, "fader_" .. i, "fader_knob_" .. i, "fader_p" .. i)
 				end
 
-				local function forget_pointers()
-					pointers = {}
+				-- Configure tuning trimmers.
+				for i = 1, 8 do
+					add_vertical_slider(view, "trimmer_" .. i, "trimmer_knob_" .. i, "pitch_adj_" .. i)
 				end
-
-				local function pointer_lost(type, id, dev, x, y, up, cnt)
-					pointers[id] = nil
-				end
-
-				local function pointer_updated(type, id, dev, x, y, btn, dn, up, cnt)
-					-- Button not pressed? Reset state of current pointer.
-					if btn & 1 == 0 then
-						pointers[id] = nil
-						return
-					end
-
-					-- Button just pressed? Find affected slider, if any.
-					if dn & 1 ~= 0 then
-						for i = 1, #sliders do
-							if sliders[i].knob.bounds:includes(x, y) then
-								local pointer = {}
-								pointer.selected_slider = i
-								pointer.relative = true
-								pointer.start_y = y
-								pointer.start_value = sliders[i].field.user_value
-								pointers[id] = pointer
-								break
-							elseif sliders[i].slider.bounds:includes(x, y) then
-								local pointer = {}
-								pointer.selected_slider = i
-								pointer.relative = false
-								pointers[id] = pointer
-								break
-							end
-						end
-					end
-
-					-- No slider selected by current pointer? Nothing to do.
-					if pointers[id] == nil then
-						return
-					end
-
-					-- A slider is selected. Update state and, indirectly,
-					-- slider knob position, based on the pointer's Y position.
-					-- It is assumed the attached IO field is an IPT_ADJUSTER
-					-- with a range of 0-100 (the default).
-
-					local pointer = pointers[id]
-					local slider_info = sliders[pointer.selected_slider]
-
-					local knob_half_height = slider_info.knob.bounds.height / 2
-					local min_y = slider_info.slider.bounds.y0 + knob_half_height
-					local max_y = slider_info.slider.bounds.y1 - knob_half_height
-
-					local new_value = 0
-					if pointer.relative then
-						-- User clicked on the knob. New value depends on how
-						-- much the knob was dragged.
-						new_value = pointer.start_value - 100 * (y - pointer.start_y) / (max_y - min_y)
-					else
-						-- User clicked elsewhere on the slider. New value
-						-- depends on the absolute position of the click.
-						new_value = 100 - 100 * (y - min_y) / (max_y - min_y)
-					end
-
-					new_value = math.floor(new_value + 0.5)
-					if new_value < 0 then new_value = 0 end
-					if new_value > 100 then new_value = 100 end
-					slider_info.field.user_value = new_value
-				end
-
-				view:set_pointer_updated_callback(pointer_updated)
-				view:set_pointer_left_callback(pointer_lost)
-				view:set_pointer_aborted_callback(pointer_lost)
-				view:set_forget_pointers_callback(forget_pointers)
 			end)
+
+		-----------------------------------------------------------------------
+		-- Slider library starts.
+		-- Can be copied as-is to other layouts.
+		-----------------------------------------------------------------------
+		local sliders = {}   -- Stores slider information.
+		local pointers = {}  -- Tracks pointer state.
+
+		-- The knob's Y position must be animated using <animate inputtag="{port_name}">.
+		-- The click area's vertical size must exactly span the range of the
+		-- knob's movement.
+		function add_vertical_slider(view, clickarea_id, knob_id, port_name)
+			local slider = {}
+
+			slider.clickarea = view.items[clickarea_id]
+			if slider.clickarea == nil then
+				emu.print_error("Slider element: '" .. clickarea_id .. "' not found.")
+				return
+			end
+
+			slider.knob = view.items[knob_id]
+			if slider.knob == nil then
+				emu.print_error("Slider knob element: '" .. knob_id .. "' not found.")
+				return
+			end
+
+			local port = file.device:ioport(port_name)
+			if port == nil then
+				emu.print_error("Port: '" .. port_name .. "' not found.")
+				return
+			end
+
+			slider.field = nil
+			for k, val in pairs(port.fields) do
+				slider.field = val
+				break
+			end
+			if slider.field == nil then
+				emu.print_error("Port: '" .. port_name .."' does not seem to be an IPT_ADJUSTER.")
+				return
+			end
+
+			table.insert(sliders, slider)
+		end
+
+		local function pointer_updated(type, id, dev, x, y, btn, dn, up, cnt)
+			-- If a button is not pressed, reset the state of the current pointer.
+			if btn & 1 == 0 then
+				pointers[id] = nil
+				return
+			end
+
+			-- If a button was just pressed, find the affected slider, if any.
+			if dn & 1 ~= 0 then
+				for i = 1, #sliders do
+					if sliders[i].knob.bounds:includes(x, y) then
+						pointers[id] = {
+							selected_slider = i,
+							relative = true,
+							start_y = y,
+							start_value = sliders[i].field.user_value }
+						break
+					elseif sliders[i].clickarea.bounds:includes(x, y) then
+						pointers[id] = {
+							selected_slider = i,
+							relative = false }
+						break
+					end
+				end
+			end
+
+			-- If there is no slider selected by the current pointer, we are done.
+			if pointers[id] == nil then
+				return
+			end
+
+			-- A slider is selected. Update state and, indirectly, slider knob position,
+			-- based on the pointer's Y position. It is assumed the attached IO field is
+			-- an IPT_ADJUSTER with a range of 0-100 (the default).
+
+			local pointer = pointers[id]
+			local slider = sliders[pointer.selected_slider]
+
+			local knob_half_height = slider.knob.bounds.height / 2
+			local min_y = slider.clickarea.bounds.y0 + knob_half_height
+			local max_y = slider.clickarea.bounds.y1 - knob_half_height
+
+			local new_value = 0
+			if pointer.relative then
+				-- User clicked on the knob. The new value will depend on how much the
+				-- knob was dragged.
+				new_value = pointer.start_value - 100 * (y - pointer.start_y) / (max_y - min_y)
+			else
+				-- User clicked elsewhere on the slider. The new value will depend on
+				-- the absolute position of the click.
+				new_value = 100 - 100 * (y - min_y) / (max_y - min_y)
+			end
+
+			new_value = math.floor(new_value + 0.5)
+			if new_value < 0 then new_value = 0 end
+			if new_value > 100 then new_value = 100 end
+			slider.field.user_value = new_value
+		end
+
+		local function pointer_left(type, id, dev, x, y, up, cnt)
+			pointers[id] = nil
+		end
+
+		local function pointer_aborted(type, id, dev, x, y, up, cnt)
+			pointers[id] = nil
+		end
+
+		local function forget_pointers()
+			pointers = {}
+		end
+
+		function install_slider_callbacks(view)
+			view:set_pointer_updated_callback(pointer_updated)
+			view:set_pointer_left_callback(pointer_left)
+			view:set_pointer_aborted_callback(pointer_aborted)
+			view:set_forget_pointers_callback(forget_pointers)
+		end
+		-----------------------------------------------------------------------
+		-- Slider library ends.
+		-----------------------------------------------------------------------
 	]]></script>
 </mamelayout>
 
diff --git a/src/mame/layout/roland_d70.lay b/src/mame/layout/roland_d70.lay
index 6f767e75eb4..7ec0d5404d8 100644
--- a/src/mame/layout/roland_d70.lay
+++ b/src/mame/layout/roland_d70.lay
@@ -248,7 +248,7 @@ copyright-holders:Felipe Sanches, m1macrophage
 
 		<element ref="slider-wider-well" id="SLIDER4"><bounds x="200" y="349" width="43" height="97"/></element>
 		<element ref="slider-well"><bounds x="217" y="357" width="10" height="82"/></element>
-		<element ref="slider-knob">
+		<element ref="slider-knob" id="SLIDER-KNOB4">
 			<animate inputtag="SLIDER4" inputmask="0x7f"/>
 			<bounds state="100" x="203" y="352" width="37" height="24"/>
 			<bounds state="0"  x="203" y="417" width="37" height="24"/>
@@ -256,7 +256,7 @@ copyright-holders:Felipe Sanches, m1macrophage
 
 		<element ref="slider-wider-well" id="SLIDER5"><bounds x="269" y="349" width="43" height="97"/></element>
 		<element ref="slider-well"><bounds x="286" y="357" width="10" height="82"/></element>
-		<element ref="slider-knob">
+		<element ref="slider-knob" id="SLIDER-KNOB5">
 			<animate inputtag="SLIDER5" inputmask="0x7f"/>
 			<bounds state="100" x="272" y="352" width="37" height="24"/>
 			<bounds state="0" x="272" y="417" width="37" height="24"/>
@@ -264,7 +264,7 @@ copyright-holders:Felipe Sanches, m1macrophage
 
 		<element ref="slider-wider-well" id="SLIDER6"><bounds x="337" y="349" width="43" height="97"/></element>
 		<element ref="slider-well"><bounds x="354" y="357" width="10" height="82"/></element>
-		<element ref="slider-knob">
+		<element ref="slider-knob" id="SLIDER-KNOB6">
 			<animate inputtag="SLIDER6" inputmask="0x7f"/>
 			<bounds state="100" x="340" y="352" width="37" height="24"/>
 			<bounds state="0"  x="340" y="417" width="37" height="24"/>
@@ -272,7 +272,7 @@ copyright-holders:Felipe Sanches, m1macrophage
 
 		<element ref="slider-wider-well" id="SLIDER7"><bounds x="405" y="349" width="43" height="97"/></element>
 		<element ref="slider-well"><bounds x="422" y="357" width="10" height="82"/></element>
-		<element ref="slider-knob">
+		<element ref="slider-knob" id="SLIDER-KNOB7">
 			<animate inputtag="SLIDER7" inputmask="0x7f"/>
 			<bounds state="100" x="408" y="352" width="37" height="24"/>
 			<bounds state="0"  x="408" y="417" width="37" height="24"/>
@@ -550,84 +550,137 @@ copyright-holders:Felipe Sanches, m1macrophage
 	<script><![CDATA[
 		file:set_resolve_tags_callback(
 			function()
-				-- These constants need to match the "slider" and
-				-- "slider-knob" element attributes.
-				local slider_height <const> = 82
-				local knob_height <const> = 24
-				local knob_slider_delta_y <const> = 5  -- slider y - knob y
-
-				local slider_deadzone <const> = math.floor(knob_height / 2) - knob_slider_delta_y
-
-				-- Local state used by the pointer update handler.
-				local sliders = {}
-				local slider_fields = {}
-				local selected = 0
-
-				-- Gather relevant elements and inputs into local state.
 				local view = file.views["Internal Layout"]
-				for i = 1, #view.items do
-					local item = view.items:at(i)
-					if item.id ~= nil and string.find(item.id, "SLIDER") == 1 then
-						local port_tag = item.id
-						local port = file.device:ioport(port_tag)
-						local field = nil
-						if port ~= nil then
-							for k, val in pairs(port.fields) do
-								field = val
-								break
-							end
-							if field == nil then
-								print("LAYOUT ERROR - Port does not have a field: " .. port_tag)
-							end
-						else
-							print("LAYOUT ERROR - Port not found: " .. port_tag)
-						end
-						table.insert(sliders, item)
-						table.insert(slider_fields, field)
+				install_slider_callbacks(view)
+
+				for i = 4, 7 do
+					add_vertical_slider(view, "SLIDER" .. i, "SLIDER-KNOB" .. i, "SLIDER" .. i)
+				end
+			end)
+		-----------------------------------------------------------------------
+		-- Slider library starts.
+		-- Can be copied as-is to other layouts.
+		-----------------------------------------------------------------------
+		local sliders = {}   -- Stores slider information.
+		local pointers = {}  -- Tracks pointer state.
+
+		-- The knob's Y position must be animated using <animate inputtag="{port_name}">.
+		-- The click area's vertical size must exactly span the range of the
+		-- knob's movement.
+		function add_vertical_slider(view, clickarea_id, knob_id, port_name)
+			local slider = {}
+
+			slider.clickarea = view.items[clickarea_id]
+			if slider.clickarea == nil then
+				emu.print_error("Slider element: '" .. clickarea_id .. "' not found.")
+				return
+			end
+
+			slider.knob = view.items[knob_id]
+			if slider.knob == nil then
+				emu.print_error("Slider knob element: '" .. knob_id .. "' not found.")
+				return
+			end
+
+			local port = file.device:ioport(port_name)
+			if port == nil then
+				emu.print_error("Port: '" .. port_name .. "' not found.")
+				return
+			end
+
+			slider.field = nil
+			for k, val in pairs(port.fields) do
+				slider.field = val
+				break
+			end
+			if slider.field == nil then
+				emu.print_error("Port: '" .. port_name .."' does not seem to be an IPT_ADJUSTER.")
+				return
+			end
+
+			table.insert(sliders, slider)
+		end
+
+		local function pointer_updated(type, id, dev, x, y, btn, dn, up, cnt)
+			-- If a button is not pressed, reset the state of the current pointer.
+			if btn & 1 == 0 then
+				pointers[id] = nil
+				return
+			end
+
+			-- If a button was just pressed, find the affected slider, if any.
+			if dn & 1 ~= 0 then
+				for i = 1, #sliders do
+					if sliders[i].knob.bounds:includes(x, y) then
+						pointers[id] = {
+							selected_slider = i,
+							relative = true,
+							start_y = y,
+							start_value = sliders[i].field.user_value }
+						break
+					elseif sliders[i].clickarea.bounds:includes(x, y) then
+						pointers[id] = {
+							selected_slider = i,
+							relative = false }
+						break
 					end
 				end
+			end
 
-				view:set_pointer_updated_callback(
-					function(type, id, dev, x, y, btn, dn, up, cnt)
-						-- No button pressed. Reset state.
-						if btn & 1 == 0 then
-							selected = 0
-							return
-						end
+			-- If there is no slider selected by the current pointer, we are done.
+			if pointers[id] == nil then
+				return
+			end
 
-						-- Button just pressed. Find affected slider.
-						if dn & 1 ~= 0 then
-							for i = 1, #sliders do
-								if sliders[i].bounds:includes(x, y) then
-									selected = i
-									break
-								end
-							end
-						end
+			-- A slider is selected. Update state and, indirectly, slider knob position,
+			-- based on the pointer's Y position. It is assumed the attached IO field is
+			-- an IPT_ADJUSTER with a range of 0-100 (the default).
 
-						-- No slider selected. Nothing to do.
-						if selected <= 0 then
-							return
-						end
+			local pointer = pointers[id]
+			local slider = sliders[pointer.selected_slider]
 
-						-- A slider is selected. Update state and, indirectly,
-						-- slider knob position, based on the pointer's Y position.
+			local knob_half_height = slider.knob.bounds.height / 2
+			local min_y = slider.clickarea.bounds.y0 + knob_half_height
+			local max_y = slider.clickarea.bounds.y1 - knob_half_height
 
-						-- It is assumed the attached IO field is an IPT_ADJUSTER
-						-- with a range of 0-100 (the default).
+			local new_value = 0
+			if pointer.relative then
+				-- User clicked on the knob. The new value will depend on how much the
+				-- knob was dragged.
+				new_value = pointer.start_value - 100 * (y - pointer.start_y) / (max_y - min_y)
+			else
+				-- User clicked elsewhere on the slider. The new value will depend on
+				-- the absolute position of the click.
+				new_value = 100 - 100 * (y - min_y) / (max_y - min_y)
+			end
 
-						local bbox = sliders[selected].bounds
-						local scale_factor = bbox.height / slider_height
-						local min_y = bbox.y0 + slider_deadzone * scale_factor
-						local max_y = bbox.y1 - slider_deadzone * scale_factor
+			new_value = math.floor(new_value + 0.5)
+			if new_value < 0 then new_value = 0 end
+			if new_value > 100 then new_value = 100 end
+			slider.field.user_value = new_value
+		end
 
-						local new_value = 100 - 100 * (y - min_y) / (max_y - min_y)
-						new_value = math.floor(new_value + 0.5)
-						if new_value < 0 then new_value = 0 end
-						if new_value > 100 then new_value = 100 end
-						slider_fields[selected].user_value = new_value
-					end)
-			end)
+		local function pointer_left(type, id, dev, x, y, up, cnt)
+			pointers[id] = nil
+		end
+
+		local function pointer_aborted(type, id, dev, x, y, up, cnt)
+			pointers[id] = nil
+		end
+
+		local function forget_pointers()
+			pointers = {}
+		end
+
+		function install_slider_callbacks(view)
+			view:set_pointer_updated_callback(pointer_updated)
+			view:set_pointer_left_callback(pointer_left)
+			view:set_pointer_aborted_callback(pointer_aborted)
+			view:set_forget_pointers_callback(forget_pointers)
+		end
+		-----------------------------------------------------------------------
+		-- Slider library ends.
+		-----------------------------------------------------------------------
 	]]></script>
 
 </mamelayout>