Random Ravings of a Red Headed Code Monkey: WP7 AccelerometerProxy in F#

With the release of the Windows Phone 7.1 SDK RC, there is now an easy way to use the emulator to simulate sensor data (such as data from the accelerometer). Unfortunately, I'm doing WP7 development in a VM and haven't yet had any luck getting the new SDK functionality to work in that environment.

I am however able to run the emulator using the WP7 Developer Tools RTW, but of course that version did not include functionality to simulate sensor data. There are a couple of options that people have identified for simulating accelerometer data (see Example using a mouse, Example using a Wiimote, Example using external app). For my needs, I decided to go with the mouse-driven approach.

While I could have easily used the C# library from the previously mentioned example, I decided instead to port that example to F#. The result is show here:

	module AccelerometerProxy

	open System
	open System.Windows
	open Microsoft.Devices
	open Microsoft.Devices.Sensors

	type AccelerometerEventArgs() =
	inherit EventArgs()
	let mutable x = 0.0
	let mutable y = 0.0
	let mutable z = 0.0
	let mutable timestamp = DateTimeOffset(DateTime.Now)
	member this.X with get() = x and set v = x <- v
	member this.Y with get() = y and set v = y <- v
	member this.Z with get() = z and set v = z <- v
	member this.Timestamp with get() = timestamp and set v = timestamp <- v

	type DeviceAccelerometer(startFunc, stopFunc) =
	let readingChangedEvent = Event<EventHandler<AccelerometerEventArgs>, AccelerometerEventArgs>()
	member x.Start () = readingChangedEvent \|> startFunc x
	member x.Stop () = stopFunc()
	member x.ReadingChanged = readingChangedEvent.Publish
	member x.OnReadingChanged eventArgs = readingChangedEvent.Trigger(x, eventArgs)

	let DefaultAccelerometer() =
	let accelerometer = new Accelerometer()

	let startFunc x event =
	(fun (x, event:Event<EventHandler<AccelerometerEventArgs>, AccelerometerEventArgs>) ->
	accelerometer.ReadingChanged.Add(fun e -> event.Trigger(x,
	AccelerometerEventArgs(X=e.X, Y=e.Y, Z=e.Z,
	Timestamp=e.Timestamp)))
	do accelerometer.Start()
	)(x, event)

	let stopFunc () = (fun() -> accelerometer.Stop())()
	(startFunc, stopFunc)

	let MouseAccelerometer() =
	let mouseDownLocation = ref (new Point())
	let isMouseDown = ref false
	let tolerance = 0.001
	let target = Application.Current.RootVisual :?> FrameworkElement

	let startFunc x event =
	(fun (x, event:Event<EventHandler<AccelerometerEventArgs>, AccelerometerEventArgs>) ->
	target.MouseLeftButtonDown.Add(fun e -> if (target.CaptureMouse()) then
	isMouseDown := true
	mouseDownLocation := e.GetPosition(target))

	target.MouseMove.Add(fun e -> if !isMouseDown then
	let position = e.GetPosition target
	let x = (position.X - (!mouseDownLocation).X) * tolerance
	let y = -(position.Y - (!mouseDownLocation).Y) * tolerance
	let timestamp = new DateTimeOffset(DateTime.Now)
	event.Trigger(x,
	new AccelerometerEventArgs(X=x, Y=y, Z=0.0,
	Timestamp=timestamp)) )

	target.MouseLeftButtonUp.Add(fun e -> target.ReleaseMouseCapture())

	target.LostMouseCapture.Add(fun e -> isMouseDown := false)
	)(x, event)

	let stopFunc () = if (!isMouseDown) then
	target.ReleaseMouseCapture()
	isMouseDown := false
	(startFunc, stopFunc)

	let GetAccelerometer() =
	let (startFunc, stopFunc) = match Microsoft.Devices.Environment.DeviceType with
	\| DeviceType.Device -> DefaultAccelerometer()
	\| _ -> MouseAccelerometer()
	DeviceAccelerometer(startFunc, stopFunc)