audio: use float32 format under the hood

Updates #2160

audio/audio.go

@@ -48,6 +48,7 @@ import (
 const (
 	channelCount           = 2
 	bitDepthInBytesInt16   = 2
+	bitDepthInBytesFloat32 = 4
 )
 
 // A Context represents a current state of audio.
@@ -188,13 +189,13 @@ func (c *Context) addPlayingPlayer(p *playerImpl) {
 	c.playingPlayers[p] = struct{}{}
 
 	// Check the source duplication
-	srcs := map[io.Reader]struct{}{}
+	srcs := map[any]struct{}{}
 	for p := range c.playingPlayers {
-		if _, ok := srcs[p.source()]; ok {
+		if _, ok := srcs[p.sourceIdent()]; ok {
 			c.err = errors.New("audio: a same source is used by multiple Player")
 			return
 		}
-		srcs[p.source()] = struct{}{}
+		srcs[p.sourceIdent()] = struct{}{}
 	}
 }
 
@@ -323,7 +324,9 @@ type Player struct {
 // A Player doesn't close src even if src implements io.Closer.
 // Closing the source is src owner's responsibility.
 func (c *Context) NewPlayer(src io.Reader) (*Player, error) {
-	pi, err := c.playerFactory.newPlayer(c, src, bitDepthInBytesInt16)
+	_, seekable := src.(io.Seeker)
+	f32Src := convert.NewFloat32BytesReaderFromInt16BytesReader(src)
+	pi, err := c.playerFactory.newPlayer(c, f32Src, seekable, src, bitDepthInBytesFloat32)
 	if err != nil {
 		return nil, err
 	}

audio/audio_test.go

@@ -116,3 +116,21 @@ func TestPauseBeforeInit(t *testing.T) {
 		t.Error(err)
 	}
 }
+
+type emptySource struct{}
+
+func (emptySource) Read(buf []byte) (int, error) {
+	return len(buf), nil
+}
+
+func TestNonSeekableSource(t *testing.T) {
+	setup()
+	defer teardown()
+
+	p, err := context.NewPlayer(emptySource{})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	p.Play()
+}

audio/context.go

@@ -24,7 +24,7 @@ func newContext(sampleRate int) (context, chan struct{}, error) {
 	ctx, ready, err := oto.NewContext(&oto.NewContextOptions{
 		SampleRate:   sampleRate,
 		ChannelCount: channelCount,
-		Format:       oto.FormatSignedInt16LE,
+		Format:       oto.FormatFloat32LE,
 	})
 	err = addErrorInfoForContextCreation(err)
 	return &contextProxy{ctx}, ready, err

audio/internal/convert/float32.go

@@ -0,0 +1,93 @@
+// Copyright 2024 The Ebitengine Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package convert
+
+import (
+	"io"
+	"math"
+)
+
+func NewFloat32BytesReaderFromInt16BytesReader(r io.Reader) io.Reader {
+	return &float32BytesReader{r: r}
+}
+
+type float32BytesReader struct {
+	r      io.Reader
+	eof    bool
+	i16Buf []byte
+}
+
+func (r *float32BytesReader) Read(buf []byte) (int, error) {
+	if r.eof && len(r.i16Buf) == 0 {
+		return 0, io.EOF
+	}
+
+	if i16LenToFill := len(buf) / 4 * 2; len(r.i16Buf) < i16LenToFill && !r.eof {
+		origLen := len(r.i16Buf)
+		if cap(r.i16Buf) < i16LenToFill {
+			r.i16Buf = append(r.i16Buf, make([]byte, i16LenToFill-origLen)...)
+		}
+
+		// Read int16 bytes.
+		n, err := r.r.Read(r.i16Buf[origLen:i16LenToFill])
+		if err != nil && err != io.EOF {
+			return 0, err
+		}
+		if err == io.EOF {
+			r.eof = true
+		}
+		r.i16Buf = r.i16Buf[:origLen+n]
+	}
+
+	// Convert int16 bytes to float32 bytes and fill buf.
+	samplesToFill := min(len(r.i16Buf)/2, len(buf)/4)
+	for i := 0; i < samplesToFill; i++ {
+		vi16l := r.i16Buf[2*i]
+		vi16h := r.i16Buf[2*i+1]
+		v := float32(int16(vi16l)|int16(vi16h)<<8) / (1 << 15)
+		vf32 := math.Float32bits(v)
+		buf[4*i] = byte(vf32)
+		buf[4*i+1] = byte(vf32 >> 8)
+		buf[4*i+2] = byte(vf32 >> 16)
+		buf[4*i+3] = byte(vf32 >> 24)
+	}
+
+	// Copy the remaining part for the next read.
+	copy(r.i16Buf, r.i16Buf[samplesToFill*2:])
+	r.i16Buf = r.i16Buf[:len(r.i16Buf)-samplesToFill*2]
+
+	return samplesToFill * 4, nil
+}
+
+func (r *float32BytesReader) Seek(offset int64, whence int) (int64, error) {
+	s, ok := r.r.(io.Seeker)
+	if !ok {
+		panic("float32: the source must be io.Seeker when seeking but not")
+	}
+	r.i16Buf = r.i16Buf[:0]
+	r.eof = false
+	n, err := s.Seek(offset/4*2, whence)
+	if err != nil {
+		return 0, err
+	}
+	return n / 2 * 4, nil
+}
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}

audio/internal/convert/float32_test.go

@@ -0,0 +1,84 @@
+// Copyright 2024 The Ebitengine Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package convert_test
+
+import (
+	"bytes"
+	"crypto/rand"
+	"io"
+	"testing"
+	"unsafe"
+
+	"github.com/hajimehoshi/ebiten/v2/audio/internal/convert"
+)
+
+func randInt16s(n int) []int16 {
+	r := make([]int16, n)
+	if _, err := rand.Read(unsafe.Slice((*byte)(unsafe.Pointer(&r[0])), len(r)*2)); err != nil {
+		panic(err)
+	}
+	return r
+}
+
+func TestFloat32(t *testing.T) {
+	cases := []struct {
+		In []int16
+	}{
+		{
+			In: nil,
+		},
+		{
+			In: []int16{-32768, 0, 32767},
+		},
+		{
+			In: []int16{0, 0, 0, 0, 0, 0, 0, 0},
+		},
+		{
+			In: randInt16s(256),
+		},
+		{
+			In: randInt16s(65536),
+		},
+	}
+	for _, c := range cases {
+		// Note that unsafe.SliceData is available as of Go 1.20.
+		var in, out []byte
+		if len(c.In) > 0 {
+			outF32 := make([]float32, len(c.In))
+			for i := range c.In {
+				outF32[i] = float32(c.In[i]) / (1 << 15)
+			}
+			in = unsafe.Slice((*byte)(unsafe.Pointer(&c.In[0])), len(c.In)*2)
+			out = unsafe.Slice((*byte)(unsafe.Pointer(&outF32[0])), len(outF32)*4)
+		}
+		r := convert.NewFloat32BytesReaderFromInt16BytesReader(bytes.NewReader(in))
+		var got []byte
+		for {
+			var buf [97]byte
+			n, err := r.Read(buf[:])
+			got = append(got, buf[:n]...)
+			if err != nil {
+				if err != io.EOF {
+					t.Fatal(err)
+				}
+				break
+			}
+		}
+		want := out
+		if !bytes.Equal(got, want) {
+			t.Errorf("got: %v, want: %v", got, want)
+		}
+	}
+}

audio/player.go

@@ -66,6 +66,8 @@ type playerImpl struct {
 	context        *Context
 	player         player
 	src            io.Reader
+	seekable       bool
+	srcIdent       any
 	stream         *timeStream
 	factory        *playerFactory
 	initBufferSize int
@@ -86,12 +88,14 @@ type playerImpl struct {
 	m sync.Mutex
 }
 
-func (f *playerFactory) newPlayer(context *Context, src io.Reader, bitDepthInBytes int) (*playerImpl, error) {
+func (f *playerFactory) newPlayer(context *Context, src io.Reader, seekable bool, srcIdent any, bitDepthInBytes int) (*playerImpl, error) {
 	f.m.Lock()
 	defer f.m.Unlock()
 
 	p := &playerImpl{
 		src:            src,
+		seekable:       seekable,
+		srcIdent:       srcIdent,
 		context:        context,
 		factory:        f,
 		lastSamples:    -1,
@@ -165,7 +169,7 @@ func (p *playerImpl) ensurePlayer() error {
 	}
 
 	if p.stream == nil {
-		s, err := newTimeStream(p.src, p.factory.sampleRate, p.bytesPerSample/channelCount)
+		s, err := newTimeStream(p.src, p.seekable, p.factory.sampleRate, p.bytesPerSample/channelCount)
 		if err != nil {
 			return err
 		}
@@ -324,8 +328,8 @@ func (p *playerImpl) SetBufferSize(bufferSize time.Duration) {
 	p.player.SetBufferSize(bufferSizeInBytes)
 }
 
-func (p *playerImpl) source() io.Reader {
+func (p *playerImpl) sourceIdent() any {
-	return p.src
+	return p.srcIdent
 }
 
 func (p *playerImpl) onContextSuspended() {
@@ -384,6 +388,7 @@ func (p *playerImpl) updatePosition() {
 
 type timeStream struct {
 	r              io.Reader
+	seekable       bool
 	sampleRate     int
 	pos            int64
 	bytesPerSample int
@@ -393,15 +398,16 @@ type timeStream struct {
 	m sync.Mutex
 }
 
-func newTimeStream(r io.Reader, sampleRate int, bitDepthInBytes int) (*timeStream, error) {
+func newTimeStream(r io.Reader, seekable bool, sampleRate int, bitDepthInBytes int) (*timeStream, error) {
 	s := &timeStream{
 		r:              r,
+		seekable:       seekable,
 		sampleRate:     sampleRate,
 		bytesPerSample: bitDepthInBytes * channelCount,
 	}
-	if seeker, ok := s.r.(io.Seeker); ok {
+	if seekable {
 		// Get the current position of the source.
-		pos, err := seeker.Seek(0, io.SeekCurrent)
+		pos, err := s.r.(io.Seeker).Seek(0, io.SeekCurrent)
 		if err != nil {
 			return nil, err
 		}
@@ -423,12 +429,11 @@ func (s *timeStream) Seek(offset int64, whence int) (int64, error) {
 	s.m.Lock()
 	defer s.m.Unlock()
 
-	seeker, ok := s.r.(io.Seeker)
+	if !s.seekable {
-	if !ok {
 		// TODO: Should this return an error?
 		panic("audio: the source must be io.Seeker when seeking but not")
 	}
-	pos, err := seeker.Seek(offset, whence)
+	pos, err := s.r.(io.Seeker).Seek(offset, whence)
 	if err != nil {
 		return pos, err
 	}