CLOSES #1471

src/core/ChipAudio.lua

@@ -183,6 +183,9 @@ end
 -- ---------------------------------------------------------------------------
 
 local musicGen = 0
+-- bumps when SOUND flips so already-queued PCM (old pan) is dropped rather
+-- than playing out the ~6s stall-tolerance queue (#1471)
+local stereoEpoch = 0
 
 function ChipAudio.playMusic(data, header, allowLoops)
   if not ensureWorker() then
@@ -204,9 +207,11 @@ function ChipAudio.playMusic(data, header, allowLoops)
                allowLoops = allowLoops, audio = slimAudio(data),
                channelVolumes = ChipSynth.getChannelVolumes(),
                channelPitches = ChipSynth.getChannelPitches(),
-               stereo = ChipSynth.getStereo() })
+               stereo = ChipSynth.getStereo(),
+               stereoEpoch = stereoEpoch })
   currentMusic = { source = source, gen = gen, threaded = true,
-                   started = false, finished = false }
+                   started = false, finished = false,
+                   stereoEpoch = stereoEpoch }
   -- playback starts in update() once the first buffer arrives (~1 frame)
   return source
 end
@@ -236,6 +241,9 @@ local function updateThreaded()
     if not buf then break end
     if buf.gen ~= m.gen then
       -- stale buffer from a superseded song: drop it
+    elseif buf.stereoEpoch ~= nil and m.stereoEpoch ~= nil
+        and buf.stereoEpoch ~= m.stereoEpoch then
+      -- stale pan mix from before a live SOUND toggle (#1471)
     elseif buf.done then
       m.finished = true
     elseif buf.error then
@@ -354,9 +362,45 @@ function ChipAudio.shutdown()
   workerReady = false
 end
 
+function ChipAudio.currentSource()
+  return currentMusic and currentMusic.source
+end
+
 function ChipAudio.setStereo(enabled)
+  enabled = not not enabled
+  if ChipSynth.getStereo() == enabled then return end
   ChipSynth.setStereo(enabled)
-  pushChannelMix()
+  stereoEpoch = stereoEpoch + 1
+  local m = currentMusic
+  if m and m.engine then
+    ChipSynth.applyStereo(m.engine)
+  end
+  if workerReady and cmdCh then
+    cmdCh:push({ cmd = "channelMix",
+                 volumes = ChipSynth.getChannelVolumes(),
+                 pitches = ChipSynth.getChannelPitches(),
+                 stereo = enabled,
+                 stereoEpoch = stereoEpoch })
+  end
+  if not m then return end
+  pendingBuf = nil
+  if outCh then outCh:clear() end
+  m.stereoEpoch = stereoEpoch
+  -- QueueableSource cannot unqueue; swap so the ~6s stall-tolerance buffers
+  -- (mixed under the previous pan) do not have to play out first (#1471)
+  if not love.audio then return end
+  local ok, source = pcall(
+    love.audio.newQueueableSource, SAMPLE_RATE, 16, 2, MUSIC_BUFFER_COUNT)
+  if not ok or not source then return end
+  local old = m.source
+  m.source = source
+  m.started = false
+  if old then pcall(old.stop, old) end
+  if not m.threaded then
+    fillSync(MUSIC_FILL_INITIAL)
+    if not musicHeld then pcall(source.play, source) end
+    m.started = true
+  end
 end
 
 function ChipAudio.getStereo()

src/core/ChipSynth.lua

@@ -294,6 +294,10 @@ function Channel.new(engine, spec, options)
     noiseSampling = false, -- Gen 2 toggle_noise
     condition = 0, -- Gen 2 set_condition / sound_jump_if
     tracks = tracks, -- Gen 2 CHANNEL_TRACKS (NR51 bits for this channel)
+    -- last Music_StereoPanning byte; remembered even while MONO so a live
+    -- SOUND toggle can re-apply it without restarting the song (#1471)
+    stereoPanning = nil,
+    forcePanning = false, -- ForceStereoPanning ($e4) ignores the SOUND option
     waveInstrument = 0,
     waveLevel = 1,
     perfectPitch = false,
@@ -406,6 +410,20 @@ function Channel:pan()
     bit.band(self.engine.pan, mask) ~= 0
 end
 
+-- Recompute CHANNEL_TRACKS from the remembered panning byte and the live
+-- STEREO flag.  ForceStereoPanning stays put either way.
+function Channel:applyStereoMix()
+  local mask = bit.lshift(1, self.hardware - 1)
+  local default = bit.bor(bit.lshift(mask, 4), mask)
+  if self.forcePanning then
+    return
+  elseif stereoEnabled and self.stereoPanning then
+    self.tracks = bit.band(self.stereoPanning, default)
+  else
+    self.tracks = default
+  end
+end
+
 function Channel:tone(ticks, register, volume, fade)
   if register >= 0x800 then
     return self:timedEvent({ silence = true }, ticks)
@@ -756,6 +774,7 @@ function Channel:nextEventGen2()
       local mask = bit.lshift(1, self.hardware - 1)
       local default = bit.bor(bit.lshift(mask, 4), mask)
       self.tracks = bit.band(packed, default)
+      self.forcePanning = true
     elseif command == 0xE5 then -- volume (global master; ignored for mix)
       self:byte()
     elseif command == 0xE6 then -- pitch_offset (big-endian)
@@ -778,8 +797,12 @@ function Channel:nextEventGen2()
     elseif command == 0xEE then -- unknownmusic0xee
       self:word()
     elseif command == 0xEF then
-      -- audio/engine.asm:1987 Music_StereoPanning: apply only when STEREO is on
+      -- audio/engine.asm:1987 Music_StereoPanning: apply only when STEREO is on.
+      -- The packed byte is kept either way so ChipSynth.applyStereo can honour
+      -- a live SOUND toggle mid-song (#1471).
       local packed = self:byte()
+      self.stereoPanning = packed
+      self.forcePanning = false
       if stereoEnabled then
         local mask = bit.lshift(1, self.hardware - 1)
         local default = bit.bor(bit.lshift(mask, 4), mask)
@@ -1298,14 +1321,30 @@ function Engine:sampleStereo()
   local left, right = 0, 0
   for _, channel in ipairs(self.channels) do
     local value = channel:sample()
-    local event = channel.event
-    if not event or event.panLeft ~= false then left = left + value end
-    if not event or event.panRight ~= false then right = right + value end
+    local panLeft, panRight
+    if self.generation == 2 then
+      -- live CHANNEL_TRACKS, not the pan baked into the current note, so a
+      -- SOUND toggle reaches the next synthesized sample (#1471)
+      panLeft, panRight = channel:pan()
+    else
+      local event = channel.event
+      panLeft = not event or event.panLeft ~= false
+      panRight = not event or event.panRight ~= false
+    end
+    if panLeft then left = left + value end
+    if panRight then right = right + value end
   end
   return analogOut(self, left, "hpfCapLeft", "lpfLeft"),
     analogOut(self, right, "hpfCapRight", "lpfRight")
 end
 
+function Engine:applyStereo()
+  if self.generation ~= 2 then return end
+  for _, channel in ipairs(self.channels) do
+    channel:applyStereoMix()
+  end
+end
+
 function Engine:sampleChannel(number)
   local selected = 0
   for _, channel in ipairs(self.channels) do
@@ -1360,4 +1399,10 @@ ChipSynth.newEngine = Engine.new
 ChipSynth.soundData = soundData
 ChipSynth.renderEffectData = renderEffectData
 
+function ChipSynth.applyStereo(engine)
+  if type(engine) == "table" and engine.applyStereo then
+    engine:applyStereo()
+  end
+end
+
 return ChipSynth

src/core/Music.lua

@@ -507,7 +507,18 @@ function Music.applyOptions(opts)
   Music.setVolumeLevel(opts and opts.musicVol or 7)
   Music.setFilterLevel(opts and opts.musicFilter or 0)
   -- engine/menus/options_menu.asm SOUND row (wOptions STEREO bit)
-  require("src.core.ChipAudio").setStereo(opts and opts.sound == "STEREO")
+  local ChipAudio = require("src.core.ChipAudio")
+  ChipAudio.setStereo(opts and opts.sound == "STEREO")
+  -- setStereo may swap the queueable source so the new pan is not sitting
+  -- behind already-mixed buffers; re-bind so volume/filter follow (#1471)
+  if state.chip then
+    local src = ChipAudio.currentSource()
+    if src then
+      state.source = src
+      applyVolume(src)
+      applyFilter(src)
+    end
+  end
 end
 
 local function sourceStopped(src)

src/core/chip_worker.lua

@@ -6,9 +6,10 @@
 -- Protocol -- main thread pushes command tables onto the "chipaudio_cmd"
 -- channel and drains produced buffers off "chipaudio_out":
 --   cmd = "play"  { gen, header, allowLoops, audio,
---                   channelVolumes?, channelPitches? }
+--                   channelVolumes?, channelPitches?, stereo?, stereoEpoch? }
 --   cmd = "stop"                                       halt production
---   cmd = "channelMix" { volumes, pitches }            per-hw volume/pitch
+--   cmd = "channelMix" { volumes, pitches, stereo?, stereoEpoch? }
+--                   stereoEpoch present: live SOUND toggle; drop lookahead
 --   cmd = "invalidate"                                 drop the bank cache
 --   cmd = "quit"                                        end the thread
 -- out buffers are tagged with the play's `gen` so the main thread can
@@ -39,6 +40,7 @@ local gen = nil        -- active song generation, or nil when stopped
 local engine = nil     -- the ChipSynth engine producing the current song
 local finished = false -- the current song ran out (non-looping)
 local data = nil       -- { audio = <slim audio tables> } for ROM bank/wave reads
+local stereoEpoch = 0  -- matches ChipAudio; stale pan buffers are dropped
 
 local function handle(cmd)
   if cmd.cmd == "play" then
@@ -56,6 +58,7 @@ local function handle(cmd)
     if cmd.stereo ~= nil then
       ChipSynth.setStereo(cmd.stereo)
     end
+    if cmd.stereoEpoch ~= nil then stereoEpoch = cmd.stereoEpoch end
     local ok, eng = pcall(ChipSynth.newEngine, data, cmd.header,
                           { allowLoops = cmd.allowLoops })
     if ok then
@@ -73,6 +76,11 @@ local function handle(cmd)
     if cmd.volumes ~= nil then ChipSynth.setChannelVolumes(cmd.volumes) end
     if cmd.pitches ~= nil then ChipSynth.setChannelPitches(cmd.pitches) end
     if cmd.stereo ~= nil then ChipSynth.setStereo(cmd.stereo) end
+    if engine and cmd.stereo ~= nil then ChipSynth.applyStereo(engine) end
+    if cmd.stereoEpoch ~= nil then
+      stereoEpoch = cmd.stereoEpoch
+      outCh:clear()
+    end
   elseif cmd.cmd == "invalidate" then
     ChipSynth.invalidateBanks()
   elseif cmd.cmd == "quit" then
@@ -95,12 +103,13 @@ while true do
     local activeGen = gen
     local ok, sd = pcall(ChipSynth.soundData, engine, BUF, 2)
     if not ok then
-      outCh:push({ gen = activeGen, error = tostring(sd) })
+      outCh:push({ gen = activeGen, error = tostring(sd),
+                   stereoEpoch = stereoEpoch })
       finished = true
     else
-      outCh:push({ gen = activeGen, sd = sd })
+      outCh:push({ gen = activeGen, sd = sd, stereoEpoch = stereoEpoch })
       if engine:finished() then
-        outCh:push({ gen = activeGen, done = true })
+        outCh:push({ gen = activeGen, done = true, stereoEpoch = stereoEpoch })
         finished = true
       end
     end