oberheim_dmx.lay: Proper tracking of pointer IDs. Easier fine adjustments. (#13319)

- Click and adjustment state is now tracked for each pointer ID individually,
  rather than globally.
- If a user selects the slider knob, the adjustment will be proportional to
  the knob movement. This allows for finer adjustments. If the user clicks
  elsewhere on the slider, the adjustment is based on the absolute position
  of the click.

Author: m1macrophage

src/mame/layout/oberheim_dmx.lay

@@ -543,13 +543,11 @@ copyright-holders:m1macrophage
 			function()
 				local id_port_index <const> = string.len("slider_knob_") + 1
 
-				-- Local state used by the pointer update handler.
-				local sliders = {}
-				local slider_knobs = {}
-				local slider_fields = {}
-				local selected = 0
+				-- 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 local 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)
@@ -575,50 +573,88 @@ copyright-holders:m1macrophage
 							print("LAYOUT ERROR - Element: 'slider_" .. slider_id .. "' does not exist.")
 						end
 
-						table.insert(sliders, slider)
-						table.insert(slider_knobs, item)
-						table.insert(slider_fields, field)
+						local slider_info = {}
+						slider_info.slider = slider
+						slider_info.knob = item
+						slider_info.field = field
+						table.insert(sliders, slider_info)
 					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
+				local function forget_pointers()
+					pointers = {}
+				end
+
+				local function pointer_lost(type, id, dev, x, y, up, cnt)
+					pointers[id] = nil
+				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
+				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. Nothing to do.
-						if selected <= 0 then
-							return
-						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
 
-						-- 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 knob_half_height = slider_knobs[selected].bounds.height / 2
-						local min_y = sliders[selected].bounds.y0 + knob_half_height
-						local max_y = sliders[selected].bounds.y1 - knob_half_height
-
-						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)
+				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)
 	]]></script>
 </mamelayout>