ebiten/examples/sinewave/main.go
2018-03-15 01:26:21 +09:00

124 lines
2.9 KiB
Go

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