audio: Change audio.SampleRate to be a const

example/audio/main.go

@@ -57,7 +57,7 @@ func square(out []int16, volume float64, freq float64, sequence float64) {
 		}
 		return
 	}
-	length := int(float64(audio.SampleRate()) / freq)
+	length := int(float64(audio.SampleRate) / freq)
 	if length == 0 {
 		panic("invalid freq")
 	}
@@ -85,7 +85,7 @@ func toBytes(l, r []int16) []byte {
 }
 
 func addNote() {
-	size := audio.SampleRate() / 60
+	size := audio.SampleRate / 60
 	notes := []float64{freqC, freqD, freqE, freqF, freqG, freqA * 2, freqB * 2}
 
 	defer func() {

example/piano/main.go

@@ -31,12 +31,12 @@ const (
 	screenHeight = 240
 )
 
-var pcm = make([]float64, 4*audio.SampleRate())
+var pcm = make([]float64, 4*audio.SampleRate)
 
 const baseFreq = 220
 
 func init() {
-	s := float64(audio.SampleRate())
+	s := float64(audio.SampleRate)
 	amp := []float64{1.0, 0.8, 0.6, 0.4, 0.2}
 	x := []float64{4.0, 2.0, 1.0, 0.5, 0.25}
 	for i := 0; i < len(pcm); i++ {

exp/audio/audio.go

@@ -19,12 +19,10 @@ import (
 )
 
 // SampleRate returns the sampling frequency (e.g. 44100).
-func SampleRate() int {
-	return audio.SampleRate
-}
+const SampleRate = audio.SampleRate
 
 // MaxChannel is a max number of channels.
-var MaxChannel = audio.MaxChannel
+const MaxChannel = audio.MaxChannel
 
 // Queue queues the given data to the given channel.
 // The given data is queued to the end of the buffer and not played immediately.
@@ -32,7 +30,7 @@ var MaxChannel = audio.MaxChannel
 // channel must be -1 or a channel index. If channel is -1, an empty channel is automatically selected.
 // If the channel is not empty, this function does nothing and returns false. This returns true otherwise.
 //
-// data's format must be linear PCM (44100Hz, 16bits, 2 channel stereo, little endian).
+// data's format must be linear PCM (44100Hz, 16bits, 2 channel stereo, little endian) without a header (e.g. RIFF header).
 func Queue(channel int, data []byte) bool {
 	return audio.Queue(channel, data)
 }

internal/audio/audio.go

@@ -23,7 +23,7 @@ type channel struct {
 	nextInsertionPosition int
 }
 
-var MaxChannel = 32
+const MaxChannel = 32
 
 var channels = make([]*channel, MaxChannel)