ebiten/exp/audio/internal/audio_openal.go

// Copyright 2015 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 !js

package internal

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"github.com/timshannon/go-openal/openal"
	"log"
	"runtime"
	"sync"
	"time"
)

var channelsMutex = sync.Mutex{}

func withChannels(f func()) {
	channelsMutex.Lock()
	defer channelsMutex.Unlock()
	f()
}

func toBytesWithPadding(l, r []int16, size int) []byte {
	if len(l) != len(r) {
		panic("len(l) must equal to len(r)")
	}
	b := &bytes.Buffer{}
	for i := 0; i < len(l); i++ {
		if err := binary.Write(b, binary.LittleEndian, []int16{l[i], r[i]}); err != nil {
			panic(err)
		}
	}
	if 0 < size-len(l) {
		if err := binary.Write(b, binary.LittleEndian, make([]int16, (size-len(l))*2)); err != nil {
			panic(err)
		}
	}
	return b.Bytes()
}

func initialize() {
	// Creating OpenAL device must be done after initializing UI. I'm not sure the reason.
	ch := make(chan struct{})
	go func() {
		runtime.LockOSThread()

		device := openal.OpenDevice("")
		context := device.CreateContext()
		context.Activate()

		if alErr := openal.GetError(); alErr != 0 {
			log.Printf("OpenAL initialize error: %d", alErr)
			close(ch)
			// Graceful ending: Audio is not available on Travis CI.
			return
		}

		audioEnabled = true
		sources := openal.NewSources(MaxChannel)
		close(ch)

		const bufferSize = 512
		emptyBytes := make([]byte, 4*bufferSize)

		for _, source := range sources {
			// 3 is the least number?
			// http://stackoverflow.com/questions/14932004/play-sound-with-openalstream
			const bufferNum = 4
			buffers := openal.NewBuffers(bufferNum)
			for _, buffer := range buffers {
				buffer.SetData(openal.FormatStereo16, emptyBytes, SampleRate)
				source.QueueBuffer(buffer)
			}
			source.Play()
			if alErr := openal.GetError(); alErr != 0 {
				panic(fmt.Sprintf("OpenAL error: %d", alErr))
			}
		}

		for {
			oneProcessed := false
			for channel, source := range sources {
				processed := source.BuffersProcessed()
				if processed == 0 {
					continue
				}

				oneProcessed = true
				buffers := make([]openal.Buffer, processed)
				source.UnqueueBuffers(buffers)
				for _, buffer := range buffers {
					l, r := loadChannelBuffer(channel, bufferSize)
					b := toBytesWithPadding(l, r, bufferSize)
					buffer.SetData(openal.FormatStereo16, b, SampleRate)
					source.QueueBuffer(buffer)
				}
				if source.State() == openal.Stopped {
					source.Rewind()
					source.Play()
				}
			}
			if !oneProcessed {
				time.Sleep(1)
			}
		}
	}()
	<-ch
}

func start() {
	// Do nothing
}