UnsafeMutablePointer in AURenderCallback - swift3

Question

I can't understand, how I should use UnsafeMutablePointer in Swift 3. Especially in AURenderCallback.
I try below code:
import Foundation
import AudioToolbox
let sineFrequency = 880.0
// MARK: User data struct
struct SineWavePlayer {
var outputUnit: AudioUnit? = nil
var startingFrameCount: Double = 0
}
// MARK: Callback function
let SineWaveRenderProc: AURenderCallback = {(inRefCon, ioActionFlags, inTimeStamp, inBusNumber, inNumberFrames, ioData) -> OSStatus in
var player = UnsafeMutablePointer<SineWavePlayer>(inRefCon)
var j = player.pointee.startingFrameCount
let cycleLength = 44100 / sineFrequency
for frame in 0..<inNumberFrames {
var buffers = UnsafeMutableAudioBufferListPointer(ioData)
UnsafeMutablePointer<Float32>(buffers[0].mData)[Int(frame)] = Float32(sin(2 * M_PI * (j / cycleLength)))
UnsafeMutablePointer<Float32>(buffers[1].mData)[Int(frame)] = Float32(sin(2 * M_PI * (j / cycleLength)))
// Or iterate through array:
// for buffer in buffers {
// UnsafeMutablePointer<Float32>(buffer.mData)[Int(frame)] = Float32(sin(2 * M_PI * (j / cycleLength)))
// }
j++
if j > cycleLength {
j -= cycleLength
}
}
player.pointee.startingFrameCount = j
return noErr
}
// MARK: Utility function
func CheckError(_ error: OSStatus, operation: String) {
guard error != noErr else {
return
}
var result: String = ""
var char = Int(error.bigEndian)
for _ in 0..<4 {
guard isprint(Int32(char&255)) == 1 else {
result = "\(error)"
break
}
result.append(String(describing: UnicodeScalar(char&255)))
char = char/256
}
print("Error: \(operation) (\(result))")
exit(1)
}
func CreateAndConnectOutputUnit(_ player: inout SineWavePlayer) {
// Generate a description that matches the output device (speakers)
var outputcd = AudioComponentDescription(componentType: kAudioUnitType_Output, componentSubType: kAudioUnitSubType_DefaultOutput, componentManufacturer: kAudioUnitManufacturer_Apple, componentFlags: 0, componentFlagsMask: 0)
let comp = AudioComponentFindNext(nil, &outputcd)
if comp == nil {
print("Can't get output unit")
exit(-1)
}
CheckError(AudioComponentInstanceNew(comp!, &player.outputUnit),
operation: "Couldn't open component for outputUnit")
// Register the render callback
var input = AURenderCallbackStruct(inputProc: SineWaveRenderProc, inputProcRefCon: &player)
CheckError(AudioUnitSetProperty(player.outputUnit!, kAudioUnitProperty_SetRenderCallback, kAudioUnitScope_Input, 0, &input, UInt32(MemoryLayout<AURenderCallbackStruct>.size)),
operation: "AudioUnitSetProperty failed")
// Initialize the unit
CheckError(AudioUnitInitialize(player.outputUnit!),
operation: "Couldn't initialize output unit")
}
func main() {
var player = SineWavePlayer()
// Set up output unit and callback
CreateAndConnectOutputUnit(&player)
// Start playing
CheckError(AudioOutputUnitStart(player.outputUnit!),
operation: "Couldn't start output unit")
// Play for 5 seconds
sleep(5)
// Clean up
AudioOutputUnitStop(player.outputUnit!)
AudioUnitUninitialize(player.outputUnit!)
AudioComponentInstanceDispose(player.outputUnit!)
}
main()
But this line of code
var player = UnsafeMutablePointer<SineWavePlayer>(inRefCon)
is not working. How to translate this line to Swift 3?
Please, help me.

Answer 1

In Swift 3, initializers cannot be used to convert pointer types. In your case, the type of inRefCon is UnsafeMutableRawPointer, so you need to use assumingMemoryBound(to:) method.
And one more, the address of player passed to the callback needs to be stable all while the sound is playing, addresses taken from inout arguments (specified by & prefix) does not fulfil this requirement.
The two things above fixed, your code would be something like this:
import Foundation
import AudioToolbox
let sineFrequency = 880.0
// MARK: User data struct
struct SineWavePlayer {
var outputUnit: AudioUnit? = nil
var startingFrameCount: Double = 0
}
// MARK: Callback function
let SineWaveRenderProc: AURenderCallback = {(inRefCon, ioActionFlags, inTimeStamp, inBusNumber, inNumberFrames, ioData) -> OSStatus in
var player = inRefCon.assumingMemoryBound(to: SineWavePlayer.self)
var j = player.pointee.startingFrameCount
let cycleLength = 44100 / sineFrequency
for frame in 0..<inNumberFrames {
var buffers = UnsafeMutableAudioBufferListPointer(ioData)
buffers?[0].mData?.assumingMemoryBound(to: Float32.self)[Int(frame)] = Float32(sin(2 * M_PI * (j / cycleLength)))
buffers?[1].mData?.assumingMemoryBound(to: Float32.self)[Int(frame)] = Float32(sin(2 * M_PI * (j / cycleLength)))
j += 1
if j > cycleLength {
j -= cycleLength
}
}
player.pointee.startingFrameCount = j
return noErr
}
// MARK: Utility function
func CheckError(_ error: OSStatus, operation: String) {
guard error != noErr else {
return
}
var result: String = ""
var char = Int(error.bigEndian)
for _ in 0..<4 {
guard isprint(Int32(char&255)) == 1 else {
result = "\(error)"
break
}
result.append(String(describing: UnicodeScalar(char&255)))
char = char/256
}
print("Error: \(operation) (\(result))")
exit(1)
}
func CreateAndConnectOutputUnit(_ playerPtr: UnsafeMutablePointer<SineWavePlayer>) {
// Generate a description that matches the output device (speakers)
var outputcd = AudioComponentDescription(componentType: kAudioUnitType_Output, componentSubType: kAudioUnitSubType_DefaultOutput, componentManufacturer: kAudioUnitManufacturer_Apple, componentFlags: 0, componentFlagsMask: 0)
let comp = AudioComponentFindNext(nil, &outputcd)
if comp == nil {
print("Can't get output unit")
exit(-1)
}
CheckError(AudioComponentInstanceNew(comp!, &playerPtr.pointee.outputUnit),
operation: "Couldn't open component for outputUnit")
// Register the render callback
var input = AURenderCallbackStruct(inputProc: SineWaveRenderProc, inputProcRefCon: playerPtr)
CheckError(AudioUnitSetProperty(playerPtr.pointee.outputUnit!, kAudioUnitProperty_SetRenderCallback, kAudioUnitScope_Input, 0, &input, UInt32(MemoryLayout<AURenderCallbackStruct>.size)),
operation: "AudioUnitSetProperty failed")
// Initialize the unit
CheckError(AudioUnitInitialize(playerPtr.pointee.outputUnit!),
operation: "Couldn't initialize output unit")
}
func main() {
let playerPtr = UnsafeMutablePointer<SineWavePlayer>.allocate(capacity: 1)
defer {playerPtr.deallocate(capacity: 1)}
playerPtr.initialize(to: SineWavePlayer())
defer {playerPtr.deinitialize()}
// Set up output unit and callback
CreateAndConnectOutputUnit(playerPtr)
// Start playing
CheckError(AudioOutputUnitStart(playerPtr.pointee.outputUnit!),
operation: "Couldn't start output unit")
// Play for 5 seconds
sleep(5)
// Clean up
AudioOutputUnitStop(playerPtr.pointee.outputUnit!)
AudioUnitUninitialize(playerPtr.pointee.outputUnit!)
AudioComponentInstanceDispose(playerPtr.pointee.outputUnit!)
}