ebiten/examples/sinewave/main.go

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// 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.
// +build example
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package main
import (
"errors"
"fmt"
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"io"
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"log"
"math"
"github.com/hajimehoshi/ebiten"
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"github.com/hajimehoshi/ebiten/audio"
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"github.com/hajimehoshi/ebiten/ebitenutil"
)
const (
screenWidth = 320
screenHeight = 240
sampleRate = 44100
frequency = 440
)
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var audioContext *audio.Context
func init() {
var err error
audioContext, err = audio.NewContext(sampleRate)
if err != nil {
log.Fatal(err)
}
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}
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// stream is an infinite stream of 440 Hz sine wave.
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type stream struct {
position int64
}
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// Read is io.Reader's Read.
//
// Read fills the data with sine wave samples.
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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
}
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// Seek is io.Seeker's Seek.
//
// whence must be io.SeekStart or io.SeekCurrent.
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func (s *stream) Seek(offset int64, whence int) (int64, error) {
const length = sampleRate / frequency
switch whence {
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case io.SeekStart:
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s.position = offset
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case io.SeekCurrent:
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s.position += offset
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default:
return 0, errors.New("whence must be io.SeekStart or io.SeekCurrent")
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}
s.position %= length * 4
return s.position, nil
}
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// Close is io.Closer's Close.
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func (s *stream) Close() error {
return nil
}
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var player *audio.Player
func update(screen *ebiten.Image) error {
if player == nil {
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// Pass the (infinite) stream to audio.NewPlayer.
// After calling Play, the stream never ends as long as the player object lives.
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var err error
player, err = audio.NewPlayer(audioContext, &stream{})
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if err != nil {
return err
}
player.Play()
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}
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if ebiten.IsRunningSlowly() {
return nil
}
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msg := fmt.Sprintf("FPS: %0.2f\nThis is an example using infinite audio stream.", ebiten.CurrentFPS())
ebitenutil.DebugPrint(screen, msg)
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return nil
}
func main() {
if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Sine Wave (Ebiten Demo)"); err != nil {
log.Fatal(err)
}
}