Golang Context.Const方法代码示例

func genMelodyArpeggio(ctx sound.Context, scale music.Scale, n int) (stream chan float64) {
	var parts []chan float64

	root := scale.Root

	for i := 0; i < n; i++ {
		if i+1 < n && rand.Float64() < 0.01 {
			from := scale.Root
			nextNote(&scale, root)
			to := scale.Root
			nextNote(&scale, root)

			part := genSlideEnvelope(ctx, from, to, time.Second/4)
			parts = append(parts, part)

		} else {
			note := scale.Root
			nextNote(&scale, root)

			part := ctx.TakeDuration(ctx.Const(note.Frequency()), time.Second/8, false)
			parts = append(parts, part)
		}
	}

	return ctx.Append(parts...)
}

func FrequencyEnvelope(ctx sound.Context) (stream chan float64) {
	var parts []chan float64
	for _, note := range Notes {
		part := ctx.TakeDuration(ctx.Const(note.Frequency()), NoteDuration, false)
		parts = append(parts, part)
	}
	return ctx.Append(parts...)
}

func FilterFormant(ctx sound.Context, input chan float64, centre, q, gain float64) (output chan float64) {
	lowerCutoff := (centre - (centre / q)) / 0.772
	upperCutoff := (centre + (centre / q)) / 1.29

	input, formant := ctx.Fork2(input)
	formant = filter.Chebyshev(ctx, formant, filter.HighPass, lowerCutoff, 0.5, 2)
	formant = filter.Chebyshev(ctx, formant, filter.LowPass, upperCutoff, 0.5, 2)
	formant = ctx.Mul(formant, ctx.Const(gain-1.0))
	return ctx.Add(input, formant)
}

func playBassSynth(ctx sound.Context, freqInput chan float64) (stream chan float64) {
	return ctx.Add(
		ctx.Mul(
			ctx.Square(
				freqInput,
				ctx.Const(0.8),
			),
		),
	)
}

func Generate(ctx sound.Context) (left, right chan float64) {
	stream := ctx.TakeDuration(
		ctx.Mul(
			ctx.Sine(
				FrequencyEnvelope(ctx),
			),
			ctx.Const(0.7),
		),
		NoteDuration*8,
		true, // Wait for a zero crossing
	)
	return ctx.Fork2(stream)
}

func Generate(ctx sound.Context) (left, right chan float64) {
	treble := SequenceTreble(ctx).Play()
	bass := SequenceBass(ctx).Play()

	trebleLeft, trebleRight := ctx.Fork2(treble)
	bassLeft, bassRight := ctx.Fork2(bass)

	left = ctx.TakeDuration(
		ctx.Add(
			ctx.Mul(trebleLeft, ctx.Const(0.3)),
			ctx.Mul(bassLeft, ctx.Const(0.4)),
		),
		NoteDuration*NumBars*3+time.Second*2,
		true,
	)

	right = ctx.TakeDuration(
		ctx.Add(
			ctx.Mul(trebleRight, ctx.Const(0.4)),
			ctx.Mul(bassRight, ctx.Const(0.3)),
		),
		NoteDuration*NumBars*3+time.Second*2,
		true,
	)

	return left, right
}

func PlayBassNote(ctx sound.Context, freqInput chan float64, duration time.Duration) (stream chan float64) {
	return ctx.TakeDuration(
		ctx.Add(
			ctx.Mul(
				ctx.Square(
					freqInput,
					ctx.Const(0.8),
				),
			),
		),
		duration,
		true,
	)
}

func SequenceBass(ctx sound.Context) (seq *sound.Sequencer) {
	melody := GenerateBassMelody()
	seq = sound.NewSequencer(ctx)

	var pos time.Duration

	for i := 0; i < NumBars; i++ {
		if rand.Float64() < 0.05 {
			freqInput := ctx.Const((<-melody).Frequency())
			note := PlayBassNote(ctx, freqInput, NoteDuration*3)
			seq.Add(pos, note)

		} else if rand.Float64() < 0.05 {
			freqInput1, freqInput2 := ctx.Fork2(ctx.Const((<-melody).Frequency()))
			note1 := PlayBassNote(ctx, freqInput1, NoteDuration)
			note2 := PlayBassNote(ctx, freqInput2, NoteDuration)
			seq.Add(pos, note1)
			seq.Add(pos+NoteDuration*2, note2)

		} else {
			freqInput := ctx.Const((<-melody).Frequency())
			note := PlayBassNote(ctx, freqInput, NoteDuration)
			seq.Add(pos, note)
		}

		pos += NoteDuration * 3
	}

	return seq
}

func SequenceTreble(ctx sound.Context) (seq *sound.Sequencer) {
	melody := GenerateTrebleMelody()
	seq = sound.NewSequencer(ctx)

	var pos time.Duration

	for i := 0; i < NumBars*3; i++ {
		var freqInput chan float64
		var duration time.Duration

		if rand.Float64() < 0.01 {
			from := (<-melody).Frequency()
			to := (<-melody).Frequency()

			freqInput = ctx.LinearEnvelope(
				from,
				NoteDuration*1/5,
				from,
				NoteDuration*8/5,
				to,
				NoteDuration*1/5+time.Millisecond,
				to,
			)
			duration = NoteDuration * 2

		} else {
			freqInput = ctx.Const((<-melody).Frequency())
			duration = NoteDuration
		}

		note := PlayTrebleNote(ctx, freqInput, duration)
		seq.Add(pos, note)
		pos += duration
	}

	return seq
}

// input should be finite and preferably short (e.g. one cycle of a triangle wave)
func KarplusStrong(ctx sound.Context, input chan float64, delaySamples uint, cutoff float64, decay float64) (output chan float64) {
	feedback := make(chan float64, ctx.StreamBufferSize)

	// Mix the input with the feedback.
	output = ctx.Add(input, feedback)

	// Fork off a copy of the output.
	output, outputCopy := ctx.Fork2(output)

	// The copy is first passed through a delay line...
	outputCopy = delay(ctx, outputCopy, delaySamples)

	// ...then filtered...
	//outputCopy = filter.Chebyshev(ctx, outputCopy, filter.LowPass, cutoff, 0.5, 2)
	outputCopy = filter.RC(ctx, outputCopy, filter.LowPass, cutoff)

	// ...and finally attenuated slightly.
	outputCopy = ctx.Mul(outputCopy, ctx.Const(decay))

	// The filtered output copy is fed back into the system.
	go pipe(outputCopy, feedback)

	return output
}

func playMelodySynth(ctx sound.Context, freqInput chan float64) (stream chan float64) {
	freqInput1, freqInput2 := ctx.Fork2(freqInput)

	return ctx.Add(
		ctx.Mul(
			ctx.Square(
				freqInput1,
				ctx.Const(0.5),
			),
			ctx.Const(0.75),
		),
		ctx.Mul(
			ctx.Saw(
				ctx.Mul(freqInput2, ctx.Const(2)),
			),
			ctx.Const(0.25),
		),
	)
}

func PlayTrebleNote(ctx sound.Context, freqInput chan float64, duration time.Duration) (stream chan float64) {
	freqInput1, freqInput2 := ctx.Fork2(freqInput)

	return ctx.TakeDuration(
		ctx.Add(
			ctx.Mul(
				ctx.Square(
					freqInput1,
					ctx.Const(0.5),
				),
				ctx.Const(0.75),
			),
			ctx.Mul(
				ctx.Saw(
					ctx.Mul(freqInput2, ctx.Const(2)),
				),
				ctx.Const(0.25),
			),
		),
		duration,
		true,
	)
}

func KarplusStrongSaw(ctx sound.Context, frequency, cutoff, decay float64) (output chan float64) {
	delaySamples := uint((1.0 / frequency) * ctx.SampleRate)
	wave := ctx.Saw(ctx.Const(frequency))
	input := ctx.Take(wave, delaySamples, true)
	return KarplusStrong(ctx, input, delaySamples, cutoff, decay)
}

func Generate(ctx sound.Context) (left, right chan float64) {
	rand.Seed(time.Now().UnixNano())

	melodyParts := make(chan chan float64)
	bassParts := make(chan chan float64)

	go func() {
		for {
			var octave int
			x := rand.Float64()
			if x < 0.3 {
				octave = 4
			} else {
				octave = 5
			}

			root := music.MakeNote(music.D, octave)
			scale := music.Scale{Root: root, Intervals: music.HarmonicMinor}

			var n int
			x = rand.Float64()
			if x < 0.2 {
				n = 3
			} else if x < 0.4 {
				n = 6
			} else if x < 0.6 {
				n = 12
			} else if x < 0.8 {
				n = 18
			} else {
				n = 24
			}

			melodyParts <- genMelodyArpeggio(ctx, scale, n)
		}
	}()

	go func() {
		for {
			var octave int
			x := rand.Float64()
			if x < 0.3 {
				octave = 3
			} else {
				octave = 2
			}

			root := music.MakeNote(music.D, octave)
			scale := music.Scale{Root: root, Intervals: music.HarmonicMinor}

			var n int
			x = rand.Float64()
			if x < 0.2 {
				n = 3
			} else if x < 0.4 {
				n = 6
			} else if x < 0.6 {
				n = 9
			} else if x < 0.8 {
				n = 12
			} else {
				n = 18
			}

			bassParts <- genBassArpeggio(ctx, scale, n)
		}
	}()

	melody := playMelodySynth(ctx, ctx.AppendStream(melodyParts))
	bass := playBassSynth(ctx, ctx.AppendStream(bassParts))

	melodyLeft, melodyRight := ctx.Fork2(melody)
	bassLeft, bassRight := ctx.Fork2(bass)

	left = ctx.TakeDuration(
		ctx.Add(
			ctx.Mul(melodyLeft, ctx.Const(0.4)),
			ctx.Mul(bassLeft, ctx.Const(0.6)),
		),
		time.Second*300,
		true,
	)

	right = ctx.TakeDuration(
		ctx.Add(
			ctx.Mul(melodyRight, ctx.Const(0.6)),
			ctx.Mul(bassRight, ctx.Const(0.4)),
		),
		time.Second*300,
		true,
	)

	return left, right
}

func genBassArpeggio(ctx sound.Context, scale music.Scale, n int) (stream chan float64) {
	var parts []chan float64

	root := scale.Root

	for i := 0; i < n; i++ {
		note := scale.Root
		nextNote(&scale, root)

		if rand.Float64() < 0.05 {
			part := ctx.TakeDuration(
				ctx.Mul(
					ctx.Const(note.Frequency()),
					ctx.Add( // Add a slight vibrato effect
						ctx.Mul(
							ctx.Sine(ctx.Const(24)),
							ctx.Const(0.01),
						),
						ctx.Const(1.0),
					),
				),
				time.Second*3/8,
				false,
			)

			parts = append(parts, part)

		} else if rand.Float64() < 0.05 {
			part1 := ctx.TakeDuration(
				ctx.Const(note.Frequency()),
				time.Second/8,
				false,
			)

			part2 := ctx.TakeDuration(
				ctx.Const(note.Frequency()),
				time.Second/8,
				false,
			)

			parts = append(parts, part1)
			parts = append(parts, ctx.TakeDuration(ctx.Silence(), time.Second/8, false))
			parts = append(parts, part2)

		} else {
			part := ctx.TakeDuration(
				ctx.Const(note.Frequency()),
				time.Second/8,
				false,
			)

			parts = append(parts, part)
			parts = append(parts, ctx.TakeDuration(ctx.Silence(), time.Second/4, false))
		}
	}

	return ctx.Append(parts...)
}