New example: Sine Wave

examples/sinewave/main.go

@@ -0,0 +1,94 @@
+// Copyright 2016 Hajime Hoshi
+//
+// 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 main
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"math"
+
+	"github.com/hajimehoshi/ebiten"
+	"github.com/hajimehoshi/ebiten/ebitenutil"
+	"github.com/hajimehoshi/ebiten/exp/audio"
+)
+
+const (
+	screenWidth  = 320
+	screenHeight = 240
+	sampleRate   = 44100
+	frequency    = 440
+)
+
+type stream struct {
+	position int64
+}
+
+func (s *stream) Read(data []byte) (int, error) {
+	if len(data)%4 != 0 {
+		return 0, errors.New("len(data) % 4 must be 0")
+	}
+	const length = sampleRate / frequency // TODO: This should be integer?
+	p := s.position / 4
+	for i := 0; i < len(data)/4; i++ {
+		const max = (1<<15 - 1) / 2
+		b := int16(math.Sin(2*math.Pi*float64(p)/length) * max)
+		data[4*i] = byte(b)
+		data[4*i+1] = byte(b >> 8)
+		data[4*i+2] = byte(b)
+		data[4*i+3] = byte(b >> 8)
+		p++
+	}
+	s.position += int64(len(data))
+	s.position %= length * 4
+	return len(data), nil
+}
+
+func (s *stream) Seek(offset int64, whence int) (int64, error) {
+	const length = sampleRate / frequency
+	switch whence {
+	case 0:
+		s.position = offset
+	case 1:
+		s.position += offset
+	case 2:
+		return 0, errors.New("whence must be 0 or 1")
+	}
+	s.position %= length * 4
+	return s.position, nil
+}
+
+var player *audio.Player
+
+func update(screen *ebiten.Image) error {
+	if player == nil {
+		var err error
+		player, err = audio.NewPlayer(&stream{}, sampleRate)
+		if err != nil {
+			return err
+		}
+		if err := player.Play(); err != nil {
+			return err
+		}
+	}
+	ebitenutil.DebugPrint(screen, fmt.Sprintf("FPS: %0.2f", ebiten.CurrentFPS()))
+	return nil
+}
+
+func main() {
+	if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Sine Wave (Ebiten Demo)"); err != nil {
+		log.Fatal(err)
+	}
+}