/
fade.go
148 lines (137 loc) · 3.73 KB
/
fade.go
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package audio
import (
"time"
"github.com/oakmound/oak/v4/audio/pcm"
)
// FadeIn wraps a reader such that it will linearly fade in over the given duration.
func FadeIn(dur time.Duration, in pcm.Reader) pcm.Reader {
perSec := in.PCMFormat().BytesPerSecond()
bytesToFadeIn := int((time.Duration(perSec) / 1000) * (dur / time.Millisecond))
return &fadeInReader{
Reader: in,
toFadeIn: bytesToFadeIn,
totalToFadeIn: bytesToFadeIn,
}
}
type fadeInReader struct {
pcm.Reader
toFadeIn, totalToFadeIn int
}
func (fir *fadeInReader) ReadPCM(b []byte) (n int, err error) {
if fir.toFadeIn == 0 {
return fir.Reader.ReadPCM(b)
}
read, err := fir.Reader.ReadPCM(b)
if err != nil {
return read, err
}
format := fir.PCMFormat()
switch format.Bits {
case 8:
for i, byt := range b[:read] {
fadeInPercent := (float64(fir.totalToFadeIn) - float64(fir.toFadeIn)) / float64(fir.totalToFadeIn)
if fadeInPercent >= 1 {
fadeInPercent = 1
}
b[i] = byte(int8(float64(int8(byt)) * fadeInPercent))
fir.toFadeIn--
}
case 16:
for i := 0; i+2 <= read; i += 2 {
fadeInPercent := (float64(fir.totalToFadeIn) - float64(fir.toFadeIn)) / float64(fir.totalToFadeIn)
if fadeInPercent >= 1 {
fadeInPercent = 1
}
i16 := int16(b[i]) + (int16(b[i+1]) << 8)
new16 := int16(float64(i16) * fadeInPercent)
b[i] = byte(new16)
b[i+1] = byte(new16 >> 8)
fir.toFadeIn -= 2
}
case 32:
for i := 0; i+4 <= read; i += 4 {
fadeInPercent := (float64(fir.totalToFadeIn) - float64(fir.toFadeIn)) / float64(fir.totalToFadeIn)
if fadeInPercent >= 1 {
fadeInPercent = 1
}
i32 := int32(b[i]) +
(int32(b[i+1]) << 8) +
(int32(b[i+2]) << 16) +
(int32(b[i+3]) << 24)
new32 := int32(float64(i32) * fadeInPercent)
b[i] = byte(new32)
b[i+1] = byte(new32 >> 8)
b[i+2] = byte(new32 >> 16)
b[i+3] = byte(new32 >> 24)
fir.toFadeIn -= 4
}
}
return read, nil
}
// FadeOut wraps a reader such that it will linearly fade out over the given duration.
func FadeOut(dur time.Duration, in pcm.Reader) pcm.Reader {
perSec := in.PCMFormat().BytesPerSecond()
bytestoFadeOut := int((time.Duration(perSec) / 1000) * (dur / time.Millisecond))
return &fadeOutReader{
Reader: in,
toFadeOut: bytestoFadeOut,
totaltoFadeOut: bytestoFadeOut,
}
}
type fadeOutReader struct {
pcm.Reader
toFadeOut, totaltoFadeOut int
}
func (fir *fadeOutReader) ReadPCM(b []byte) (n int, err error) {
if fir.toFadeOut == 0 {
return fir.Reader.ReadPCM(b)
}
read, err := fir.Reader.ReadPCM(b)
if err != nil {
return read, err
}
format := fir.PCMFormat()
switch format.Bits {
case 8:
for i, byt := range b[:read] {
fadeOutPercent := float64(fir.toFadeOut) / float64(fir.totaltoFadeOut)
if fadeOutPercent <= 0 {
fadeOutPercent = 0
}
b[i] = byte(int8(float64(int8(byt)) * fadeOutPercent))
fir.toFadeOut--
}
case 16:
for i := 0; i+2 <= read; i += 2 {
fadeOutPercent := float64(fir.toFadeOut) / float64(fir.totaltoFadeOut)
if fadeOutPercent <= 0 {
fadeOutPercent = 0
}
i16 := int16(b[i]) + (int16(b[i+1]) << 8)
new16 := int16(float64(i16) * fadeOutPercent)
b[i] = byte(new16)
b[i+1] = byte(new16 >> 8)
fir.toFadeOut -= 2
}
case 32:
for i := 0; i+4 <= read; i += 4 {
fadeOutPercent := float64(fir.toFadeOut) / float64(fir.totaltoFadeOut)
if fadeOutPercent <= 0 {
fadeOutPercent = 0
}
i32 := int32(b[i]) +
(int32(b[i+1]) << 8) +
(int32(b[i+2]) << 16) +
(int32(b[i+3]) << 24)
new32 := int32(float64(i32) * fadeOutPercent)
b[i] = byte(new32)
b[i+1] = byte(new32 >> 8)
b[i+2] = byte(new32 >> 16)
b[i+3] = byte(new32 >> 24)
fir.toFadeOut -= 4
}
}
return read, nil
}
var _ pcm.Reader = &fadeOutReader{}
var _ pcm.Reader = &fadeInReader{}