Sdl backend (#670)

* [audio] added sdl audio backend and in-tree atrac9 decoder

* [input] replaced per-platform pad readers with sdl gamepad input

* [video] added sdl window and host display plumbing

* [gui] added host display options and per-game render settings

* [bink] synced host movie playback to the guest audio clock

* [cpu] hooked windows write faults into guest image tracking

* [perf] added guest and render profiling, reserved host cpu lanes

* [kernel] fixed stale pthread mutex handle alias

* [host] wired the sdl session, save-data paths and project references

* [audio] hoisted ajm trace stackalloc out of its loop

* [video] Add guest image sync setting

* [build] Strip native symbols

* reuse

src/SharpEmu.Libs/Audio/Atrac9DecodeState.cs

@@ -0,0 +1,409 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using System.Buffers.Binary;
+using LibAtrac9;
+
+namespace SharpEmu.Libs.Audio;
+
+internal enum Atrac9PcmEncoding
+{
+    Signed16,
+    Signed32,
+    Float,
+}
+
+internal readonly record struct Atrac9DecodeResult(
+    int Status,
+    int InputConsumed,
+    int OutputWritten,
+    ulong TotalDecodedSamples,
+    uint Frames);
+
+internal sealed class Atrac9DecodeState
+{
+    internal const int ResultNotInitialized = 0x00000001;
+    internal const int ResultInvalidData = 0x00000002;
+    internal const int ResultInvalidParameter = 0x00000004;
+    internal const int ResultPartialInput = 0x00000008;
+    internal const int ResultNotEnoughRoom = 0x00000010;
+    internal const int ResultCodecError = 0x40000000;
+
+    private const int MaxContainerHeaderBytes = 8 * 1024;
+
+    private enum ContainerScan
+    {
+        NotContainer,
+        NeedMoreData,
+        Found,
+    }
+
+    private readonly object _gate = new();
+    private Atrac9Decoder? _decoder;
+    private byte[]? _configData;
+    private byte[]? _compressed;
+    private short[][]? _planarPcm;
+    private byte[]? _containerHeader;
+    private int _containerHeaderLength;
+    private int _compressedLength;
+    private ulong _totalDecodedSamples;
+
+    public Atrac9Config? Config
+    {
+        get
+        {
+            lock (_gate)
+            {
+                return _decoder?.Config;
+            }
+        }
+    }
+
+    public bool TryInitialize(ReadOnlySpan<byte> configData)
+    {
+        if (configData.Length < 4)
+        {
+            return false;
+        }
+
+        lock (_gate)
+        {
+            try
+            {
+                var normalizedConfig = configData[..4].ToArray();
+                var decoder = new Atrac9Decoder();
+                decoder.Initialize(normalizedConfig);
+                var config = decoder.Config;
+
+                _decoder = decoder;
+                _configData = normalizedConfig;
+                _compressed = new byte[config.SuperframeBytes];
+                _planarPcm = CreatePcmBuffer(config.ChannelCount, config.SuperframeSamples);
+                _compressedLength = 0;
+                _totalDecodedSamples = 0;
+                _containerHeaderLength = 0;
+                Trace(
+                    $"initialized config={Convert.ToHexString(normalizedConfig)} channels={config.ChannelCount} " +
+                    $"rate={config.SampleRate} frame_samples={config.FrameSamples} " +
+                    $"superframe_samples={config.SuperframeSamples} superframe_bytes={config.SuperframeBytes} " +
+                    $"frames_per_superframe={config.FramesPerSuperframe}");
+                return true;
+            }
+            catch (Exception exception) when (
+                exception is ArgumentException or InvalidDataException or InvalidOperationException)
+            {
+                Clear();
+                return false;
+            }
+        }
+    }
+
+    public void Reset()
+    {
+        lock (_gate)
+        {
+            if (_configData is null)
+            {
+                Clear();
+                return;
+            }
+
+            var decoder = new Atrac9Decoder();
+            decoder.Initialize((byte[])_configData.Clone());
+            _decoder = decoder;
+            _compressedLength = 0;
+            _totalDecodedSamples = 0;
+            _containerHeaderLength = 0;
+            if (_compressed is not null)
+            {
+                Array.Clear(_compressed);
+            }
+        }
+    }
+
+    public Atrac9DecodeResult Decode(
+        ReadOnlySpan<byte> input,
+        Span<byte> output,
+        Atrac9PcmEncoding encoding,
+        int requestedChannels,
+        bool multipleFrames)
+    {
+        lock (_gate)
+        {
+            if (_decoder is null || _compressed is null || _planarPcm is null)
+            {
+                return new Atrac9DecodeResult(
+                    ResultNotInitialized,
+                    0,
+                    0,
+                    _totalDecodedSamples,
+                    0);
+            }
+
+            var config = _decoder.Config;
+            var channels = requestedChannels > 0 ? requestedChannels : config.ChannelCount;
+            if (channels is < 1 or > 16)
+            {
+                return new Atrac9DecodeResult(
+                    ResultInvalidParameter,
+                    0,
+                    0,
+                    _totalDecodedSamples,
+                    0);
+            }
+
+            var bytesPerSample = GetBytesPerSample(encoding);
+            var outputBytesPerSuperframe = checked(config.SuperframeSamples * channels * bytesPerSample);
+            var consumed = 0;
+            var written = 0;
+            uint frames = 0;
+            var status = 0;
+
+            while (_compressedLength == config.SuperframeBytes ||
+                   consumed < input.Length)
+            {
+                // Titles that stream whole .at9 files hand AJM the RIFF/WAVE
+                // container rather than a pointer into its `data` chunk, so the
+                // stream has to be advanced past the header before the first
+                // superframe — otherwise every job fails with invalid data and
+                // the title drops the voice. This is checked at every superframe
+                // boundary, not just after initialize, because a looping voice
+                // rewinds to the file header without reinitialising.
+                if (_compressedLength == 0 && (_containerHeaderLength != 0 || consumed < input.Length))
+                {
+                    var scan = ScanContainerHeader(input[consumed..], out var headerBytes);
+                    if (scan == ContainerScan.NeedMoreData)
+                    {
+                        consumed = input.Length;
+                        status |= ResultPartialInput;
+                        break;
+                    }
+
+                    if (scan == ContainerScan.Found)
+                    {
+                        _containerHeader = null;
+                        _containerHeaderLength = 0;
+                        consumed += headerBytes;
+                        continue;
+                    }
+                }
+
+                if (_compressedLength < config.SuperframeBytes)
+                {
+                    var copied = Math.Min(config.SuperframeBytes - _compressedLength, input.Length - consumed);
+                    input.Slice(consumed, copied).CopyTo(_compressed.AsSpan(_compressedLength));
+                    _compressedLength += copied;
+                    consumed += copied;
+                }
+
+                if (_compressedLength < config.SuperframeBytes)
+                {
+                    status |= ResultPartialInput;
+                    break;
+                }
+
+                if (output.Length - written < outputBytesPerSuperframe)
+                {
+                    status |= ResultNotEnoughRoom;
+                    break;
+                }
+
+                try
+                {
+                    _decoder.Decode(_compressed, _planarPcm);
+                }
+                catch (Exception exception) when (
+                    exception is ArgumentException or InvalidDataException or InvalidOperationException or IndexOutOfRangeException)
+                {
+                    Trace(
+                        $"decode_failed superframe_bytes={config.SuperframeBytes} " +
+                        $"config={Convert.ToHexString(_configData ?? [])} " +
+                        $"head={Convert.ToHexString(_compressed.AsSpan(0, Math.Min(16, _compressed.Length)))} " +
+                        $"error={exception.GetType().Name}: {exception.Message}");
+                    _compressedLength = 0;
+                    return new Atrac9DecodeResult(
+                        status | ResultInvalidData | ResultCodecError,
+                        consumed,
+                        written,
+                        _totalDecodedSamples,
+                        frames);
+                }
+
+                WriteInterleaved(
+                    _planarPcm,
+                    output.Slice(written, outputBytesPerSuperframe),
+                    config.SuperframeSamples,
+                    channels,
+                    encoding);
+
+                written += outputBytesPerSuperframe;
+                _compressedLength = 0;
+                _totalDecodedSamples += unchecked((uint)config.SuperframeSamples);
+                frames += unchecked((uint)config.FramesPerSuperframe);
+
+                if (!multipleFrames)
+                {
+                    break;
+                }
+            }
+
+            return new Atrac9DecodeResult(
+                status,
+                consumed,
+                written,
+                _totalDecodedSamples,
+                frames);
+        }
+    }
+
+    private ContainerScan ScanContainerHeader(ReadOnlySpan<byte> input, out int inputHeaderBytes)
+    {
+        inputHeaderBytes = 0;
+
+        if (_containerHeaderLength == 0 &&
+            (input.Length < 4 || !input[..4].SequenceEqual("RIFF"u8)))
+        {
+            return ContainerScan.NotContainer;
+        }
+
+        _containerHeader ??= new byte[MaxContainerHeaderBytes];
+        var previousLength = _containerHeaderLength;
+        var copied = Math.Min(input.Length, MaxContainerHeaderBytes - previousLength);
+        input[..copied].CopyTo(_containerHeader.AsSpan(previousLength));
+        var totalLength = previousLength + copied;
+
+        if (!TryFindRiffDataOffset(_containerHeader.AsSpan(0, totalLength), out var dataOffset))
+        {
+            if (totalLength >= MaxContainerHeaderBytes)
+            {
+                // Not a shape we understand — fall back to treating the stream
+                // as raw superframes rather than swallowing it forever. The
+                // scratch is dropped without advancing the caller's cursor, so
+                // the bytes are still decoded normally.
+                Trace($"container_scan_gave_up bytes={totalLength}");
+                _containerHeader = null;
+                _containerHeaderLength = 0;
+                return ContainerScan.NotContainer;
+            }
+
+            _containerHeaderLength = totalLength;
+            return ContainerScan.NeedMoreData;
+        }
+
+        inputHeaderBytes = dataOffset - previousLength;
+        Trace($"container_header_skipped bytes={dataOffset} from_this_input={inputHeaderBytes}");
+        return ContainerScan.Found;
+    }
+
+    private static bool TryFindRiffDataOffset(ReadOnlySpan<byte> header, out int dataOffset)
+    {
+        dataOffset = 0;
+        if (header.Length < 12 ||
+            !header[..4].SequenceEqual("RIFF"u8) ||
+            !header.Slice(8, 4).SequenceEqual("WAVE"u8))
+        {
+            return false;
+        }
+
+        var offset = 12;
+        while (offset + 8 <= header.Length)
+        {
+            var chunkId = header.Slice(offset, 4);
+            var chunkSize = BinaryPrimitives.ReadUInt32LittleEndian(header.Slice(offset + 4, 4));
+            offset += 8;
+            if (chunkId.SequenceEqual("data"u8))
+            {
+                dataOffset = offset;
+                return true;
+            }
+
+            // RIFF chunks are word aligned.
+            var advance = chunkSize + (chunkSize & 1);
+            if (advance > (ulong)(int.MaxValue - offset))
+            {
+                return false;
+            }
+
+            offset += (int)advance;
+        }
+
+        return false;
+    }
+
+    private static short[][] CreatePcmBuffer(int channels, int samples)
+    {
+        var result = new short[channels][];
+        for (var channel = 0; channel < channels; channel++)
+        {
+            result[channel] = new short[samples];
+        }
+
+        return result;
+    }
+
+    private static int GetBytesPerSample(Atrac9PcmEncoding encoding) =>
+        encoding switch
+        {
+            Atrac9PcmEncoding.Signed16 => sizeof(short),
+            Atrac9PcmEncoding.Signed32 => sizeof(int),
+            Atrac9PcmEncoding.Float => sizeof(float),
+            _ => throw new ArgumentOutOfRangeException(nameof(encoding)),
+        };
+
+    private static void WriteInterleaved(
+        short[][] source,
+        Span<byte> destination,
+        int samples,
+        int channels,
+        Atrac9PcmEncoding encoding)
+    {
+        var offset = 0;
+        for (var sample = 0; sample < samples; sample++)
+        {
+            for (var channel = 0; channel < channels; channel++)
+            {
+                var sourceChannel = Math.Min(channel, source.Length - 1);
+                var value = source[sourceChannel][sample];
+                switch (encoding)
+                {
+                    case Atrac9PcmEncoding.Signed16:
+                        BinaryPrimitives.WriteInt16LittleEndian(destination[offset..], value);
+                        offset += sizeof(short);
+                        break;
+                    case Atrac9PcmEncoding.Signed32:
+                        BinaryPrimitives.WriteInt32LittleEndian(destination[offset..], value << 16);
+                        offset += sizeof(int);
+                        break;
+                    case Atrac9PcmEncoding.Float:
+                        BinaryPrimitives.WriteInt32LittleEndian(
+                            destination[offset..],
+                            BitConverter.SingleToInt32Bits(value / 32768.0f));
+                        offset += sizeof(float);
+                        break;
+                    default:
+                        throw new ArgumentOutOfRangeException(nameof(encoding));
+                }
+            }
+        }
+    }
+
+    private static void Trace(string message)
+    {
+        if (string.Equals(Environment.GetEnvironmentVariable("SHARPEMU_LOG_AJM"), "1", StringComparison.Ordinal))
+        {
+            Console.Error.WriteLine($"[LOADER][TRACE] ajm.at9.{message}");
+        }
+    }
+
+    private void Clear()
+    {
+        _decoder = null;
+        _configData = null;
+        _compressed = null;
+        _planarPcm = null;
+        _containerHeader = null;
+        _containerHeaderLength = 0;
+        _compressedLength = 0;
+        _totalDecodedSamples = 0;
+    }
+}

src/SharpEmu.Libs/Audio/AudioOutExports.cs

@@ -44,6 +44,7 @@ public static class AudioOutExports
             int channels,
             int bytesPerSample,
             bool isFloat,
+            bool preservesGuestFormat,
             IHostAudioStream? backend)
         {
             UserId = userId;
@@ -54,6 +55,7 @@ public static class AudioOutExports
             Channels = channels;
             BytesPerSample = bytesPerSample;
             IsFloat = isFloat;
+            PreservesGuestFormat = preservesGuestFormat;
             Backend = backend;
         }
 
@@ -65,6 +67,7 @@ public static class AudioOutExports
         public int Channels { get; }
         public int BytesPerSample { get; }
         public bool IsFloat { get; }
+        public bool PreservesGuestFormat { get; }
         public IHostAudioStream? Backend { get; }
         public object SubmissionGate { get; } = new();
         public volatile float Volume = 1.0f;
@@ -140,6 +143,7 @@ public static class AudioOutExports
         }
 
         IHostAudioStream? backend = null;
+        var preservesGuestFormat = false;
         string backendName;
         try
         {
@@ -152,7 +156,18 @@ public static class AudioOutExports
             else
             {
                 var audio = HostPlatform.Current.Audio;
-                backend = audio.OpenStereoPcm16Stream(frequency);
+                if (audio is IHostPcmAudioOutput pcmAudio)
+                {
+                    backend = pcmAudio.OpenPcmStream(
+                        frequency,
+                        channels,
+                        isFloat ? HostPcmFormat.Float32 : HostPcmFormat.Signed16);
+                    preservesGuestFormat = true;
+                }
+                else
+                {
+                    backend = audio.OpenStereoPcm16Stream(frequency);
+                }
                 backendName = audio.BackendName;
             }
         }
@@ -173,6 +188,7 @@ public static class AudioOutExports
             channels,
             bytesPerSample,
             isFloat,
+            preservesGuestFormat,
             backend);
         Console.Error.WriteLine(
             $"[LOADER][INFO] AudioOut port {handle}: {frequency} Hz, " +
@@ -321,18 +337,13 @@ public static class AudioOutExports
                 return ctx.SetReturn(0);
             }
 
-            var outputLength = checked((int)port.BufferLength * AudioPcmConversion.OutputFrameSize);
+            var outputLength = port.PreservesGuestFormat
+                ? port.BufferByteLength
+                : checked((int)port.BufferLength * AudioPcmConversion.OutputFrameSize);
             var output = ArrayPool<byte>.Shared.Rent(outputLength);
             try
             {
-                AudioPcmConversion.ConvertToStereoPcm16(
-                    source,
-                    output.AsSpan(0, outputLength),
-                    checked((int)port.BufferLength),
-                    port.Channels,
-                    port.BytesPerSample,
-                    port.IsFloat,
-                    port.Volume);
+                ConvertForHost(port, source, output.AsSpan(0, outputLength));
                 if (!port.Backend.Submit(output.AsSpan(0, outputLength)))
                 {
                     port.PaceSilence();
@@ -449,17 +460,11 @@ public static class AudioOutExports
 
                     TraceOutput(output.Handle, output.Port, source);
 
-                    output.HostBufferLength = checked(
-                        (int)output.Port.BufferLength * AudioPcmConversion.OutputFrameSize);
+                    output.HostBufferLength = output.Port.PreservesGuestFormat
+                        ? output.Port.BufferByteLength
+                        : checked((int)output.Port.BufferLength * AudioPcmConversion.OutputFrameSize);
                     output.HostBuffer = ArrayPool<byte>.Shared.Rent(output.HostBufferLength);
-                    AudioPcmConversion.ConvertToStereoPcm16(
-                        source,
-                        output.HostBuffer.AsSpan(0, output.HostBufferLength),
-                        checked((int)output.Port.BufferLength),
-                        output.Port.Channels,
-                        output.Port.BytesPerSample,
-                        output.Port.IsFloat,
-                        output.Port.Volume);
+                    ConvertForHost(output.Port, source, output.HostBuffer.AsSpan(0, output.HostBufferLength));
                 }
                 finally
                 {
@@ -513,6 +518,24 @@ public static class AudioOutExports
         (ulong)candidate.BufferLength * current.Frequency >
         (ulong)current.BufferLength * candidate.Frequency;
 
+    private static void ConvertForHost(PortState port, ReadOnlySpan<byte> source, Span<byte> destination)
+    {
+        if (port.PreservesGuestFormat)
+        {
+            AudioPcmConversion.CopyWithVolume(source, destination, port.IsFloat, port.Volume);
+            return;
+        }
+
+        AudioPcmConversion.ConvertToStereoPcm16(
+            source,
+            destination,
+            checked((int)port.BufferLength),
+            port.Channels,
+            port.BytesPerSample,
+            port.IsFloat,
+            port.Volume);
+    }
+
     private static void TraceOutput(int handle, PortState port, ReadOnlySpan<byte> source)
     {
         if (!_traceOutput)

src/SharpEmu.Libs/Audio/AudioPcmConversion.cs

@@ -43,6 +43,46 @@ internal static class AudioPcmConversion
         }
     }
 
+    /// <summary>
+    /// Copies interleaved PCM without changing its channel layout. SDL can convert
+    /// this directly to the physical device, which preserves surround mixes that
+    /// would otherwise be truncated to the first two guest channels.
+    /// </summary>
+    public static void CopyWithVolume(
+        ReadOnlySpan<byte> source,
+        Span<byte> destination,
+        bool isFloat,
+        float volume)
+    {
+        var clampedVolume = Math.Clamp(volume, 0.0f, 1.0f);
+        if (clampedVolume >= 1.0f)
+        {
+            source.CopyTo(destination);
+            return;
+        }
+
+        if (isFloat)
+        {
+            for (var offset = 0; offset < source.Length; offset += sizeof(float))
+            {
+                var sample = BinaryPrimitives.ReadSingleLittleEndian(source.Slice(offset, sizeof(float)));
+                BinaryPrimitives.WriteSingleLittleEndian(
+                    destination.Slice(offset, sizeof(float)),
+                    sample * clampedVolume);
+            }
+
+            return;
+        }
+
+        for (var offset = 0; offset < source.Length; offset += sizeof(short))
+        {
+            var sample = BinaryPrimitives.ReadInt16LittleEndian(source.Slice(offset, sizeof(short)));
+            BinaryPrimitives.WriteInt16LittleEndian(
+                destination.Slice(offset, sizeof(short)),
+                ApplyVolume(sample, clampedVolume));
+        }
+    }
+
     private static short ReadSample(
         ReadOnlySpan<byte> frame,
         int channel,