metro-puzzle-jp/tools/gensound/main.go

// Genererar placeholder-ljud tills riktiga inspelningar finns:
//
//	go run ./tools/gensound
//
// Skriver resources/sound/melody-approach.wav (en kort pentatonisk
// avgångsmelodi i japansk stationsstil, spelas när tåget är på väg in) och
// resources/sound/door-chime.wav (dörrsignal strax före avgång). 16-bit
// mono 44,1 kHz, syntetiserade med enkla vågformer så att allt är
// deterministiskt.
package main

import (
	"encoding/binary"
	"fmt"
	"math"
	"os"
	"path/filepath"
)

const rate = 44100

type note struct {
	freq float64 // Hz, 0 = paus
	dur  float64 // sekunder
}

// Pentatonisk melodi (C-dur-pentatonik), två takter.
var approachMelody = []note{
	{523.25, 0.18}, {587.33, 0.18}, {659.25, 0.18}, {783.99, 0.36},
	{880.00, 0.18}, {783.99, 0.18}, {659.25, 0.18}, {523.25, 0.36},
	{0, 0.12},
	{659.25, 0.18}, {783.99, 0.18}, {880.00, 0.18}, {1046.50, 0.54},
}

// Dörrsignal: två toner växelvis.
var doorChime = []note{
	{1318.51, 0.14}, {1046.50, 0.14}, {1318.51, 0.14}, {1046.50, 0.14},
	{1318.51, 0.14}, {1046.50, 0.14}, {1318.51, 0.14}, {1046.50, 0.28},
}

func render(notes []note, attack, release float64, overtone float64) []int16 {
	var out []int16
	for _, n := range notes {
		samples := int(n.dur * rate)
		for i := 0; i < samples; i++ {
			if n.freq == 0 {
				out = append(out, 0)
				continue
			}
			t := float64(i) / rate
			env := 1.0
			if t < attack {
				env = t / attack
			}
			if rem := n.dur - t; rem < release {
				env *= rem / release
			}
			v := math.Sin(2*math.Pi*n.freq*t) + overtone*math.Sin(2*math.Pi*2*n.freq*t)
			v = v / (1 + overtone) * env * 0.5
			out = append(out, int16(v*32767))
		}
	}
	return out
}

func writeWAV(path string, pcm []int16) error {
	f, err := os.Create(path)
	if err != nil {
		return err
	}
	defer f.Close()
	dataLen := uint32(len(pcm) * 2)
	hdr := []any{
		[]byte("RIFF"), uint32(36 + dataLen), []byte("WAVE"),
		[]byte("fmt "), uint32(16), uint16(1), uint16(1), uint32(rate), uint32(rate * 2), uint16(2), uint16(16),
		[]byte("data"), dataLen,
	}
	for _, h := range hdr {
		if err := binary.Write(f, binary.LittleEndian, h); err != nil {
			return err
		}
	}
	return binary.Write(f, binary.LittleEndian, pcm)
}

// chatter syntetiserar sex sekunder loopbart stationssorl: lågpassat brus
// med stavelseliknande amplitudmodulation från en deterministisk LCG.
func chatter(seconds float64) []int16 {
	n := int(seconds * rate)
	out := make([]int16, n)
	var lcg uint32 = 12345
	next := func() float64 { lcg = lcg*1664525 + 1013904223; return float64(lcg>>8)/float64(1<<24)*2 - 1 }
	lp := 0.0
	env, envTarget, envT := 0.3, 0.3, 0.0
	for i := 0; i < n; i++ {
		t := float64(i) / rate
		// ny "stavelse" var 120–250 ms
		if t >= envT {
			envTarget = 0.1 + 0.6*math.Abs(next())
			envT = t + 0.12 + 0.13*math.Abs(next())
		}
		env += (envTarget - env) * 0.002
		lp += (next() - lp) * 0.08 // lågpass ≈ 600 Hz
		v := lp * env * 0.6
		// mjuk in-/utfasning för sömlös loop
		fade := math.Min(1, math.Min(t, seconds-t)/0.2)
		out[i] = int16(v * fade * 32767)
	}
	return out
}

func main() {
	out := filepath.Join(repoRoot(), "resources", "sound")
	must(os.MkdirAll(out, 0o755))
	must(writeWAV(filepath.Join(out, "melody-approach.wav"), render(approachMelody, 0.01, 0.06, 0.3)))
	must(writeWAV(filepath.Join(out, "door-chime.wav"), render(doorChime, 0.005, 0.04, 0.1)))
	must(writeWAV(filepath.Join(out, "chatter.wav"), chatter(6)))
	fmt.Println("skrev", filepath.Join(out, "melody-approach.wav"), ", door-chime.wav och chatter.wav")
}

func repoRoot() string {
	dir, _ := os.Getwd()
	for {
		if _, err := os.Stat(filepath.Join(dir, "go.mod")); err == nil {
			return dir
		}
		parent := filepath.Dir(dir)
		if parent == dir {
			must(fmt.Errorf("hittade ingen go.mod"))
		}
		dir = parent
	}
}

func must(err error) {
	if err != nil {
		fmt.Fprintln(os.Stderr, "gensound:", err)
		os.Exit(1)
	}
}