“Submarine Challenge” is a small game on Douyin, which uses facial recognition to drive submarines through obstacles. It is very popular recently, and I believe many people have played it.

On a whim I use Android custom View also masturbated a, found that as long as there is a good idea, without advanced technology can still develop a fun application. The development process is out to share with you.

Project address: github.com/vitaviva/ug…

The basic idea

The overall game view can be divided into three layers:

Camera: Handle camera preview and face recognition
Background: Handles obstruction-related logic
Foreground: Submarine foreground

The code is also organized by the three layers above, and the layout of the game interface can be easily understood as the superposition of three layers of views, and then the related work is done in each layer


<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

  <! - camera - >
  <TextureView
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

  <! - foreground - >
  <com.my.ugame.bg.BackgroundView
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
        
  <! Prospects -- -- -- >
  <com.my.ugame.fg.ForegroundView
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</Framelayout>
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Development will involve the use of the following technologies, no sophisticated, are common goods:

Camera: use Camera2 for camera preview and face recognition
Custom View: Defines and controls obstacles and submarines
Property animation: Controls the movement of obstacles and submarines and various dynamic effects

Get off your back and look at things first! The implementation of each part of the code is described below.

Background

Bar

Firstly, the obstacle base class Bar is defined, which is mainly responsible for drawing bitmap resources to the specified area. Since the height of the obstacle is random when it is periodically refreshed from the right side of the screen, the x, Y, W and H of its drawing area need to be set dynamically

/** * Obstacle base class */
sealed class Bar(context: Context) {

    protected open valbmp = context.getDrawable(R.mipmap.bar)!! .toBitmap()protected abstract val srcRect: Rect

    private lateinit var dstRect: Rect

    private val paint = Paint()

    var h = 0F
        set(value) {
            field = value
            dstRect = Rect(0.0, w.toInt(), h.toInt())
        }

    var w = 0F
        set(value) {
            field = value
            dstRect = Rect(0.0, w.toInt(), h.toInt())
        }

    var x = 0F
        set(value) {
            view.x = value
            field = value
        }

    val y
        get() = view.y

    internal val view bylazy { BarView(context) { it? .apply { drawBitmap( bmp, srcRect, dstRect, paint ) } } } }internal class BarView(context: Context? .private val block: (Canvas?) -> Unit) :
    View(context) {

    override fun onDraw(canvas: Canvas?). {
        block((canvas))
    }
}
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Obstacles are divided into upper and lower parts. Since the same resource is used, they should be treated differently when drawing. Therefore, two subclasses are defined: UpBar and DnBar

/** * Obstacles above the screen */
class UpBar(context: Context, container: ViewGroup) : Bar(context) {

    private val _srcRect by lazy(LazyThreadSafetyMode.NONE) {
        Rect(0, (bmp.height * (1 - (h / container.height))).toInt(), bmp.width, bmp.height)
    }
    override val srcRect: Rect
        get() = _srcRect

}
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Resources on the obstacles below are drawn after being rotated 180 degrees

/** * Obstacles below the screen */
class DnBar(context: Context, container: ViewGroup) : Bar(context) {

    override val bmp = super.bmp.let {
        Bitmap.createBitmap(
            it, 0.0, it.width, it.height,
            Matrix().apply { postRotate(-180F)},true)}private val _srcRect by lazy(LazyThreadSafetyMode.NONE) {
        Rect(0.0, bmp.width, (bmp.height * (h / container.height)).toInt())
    }

    override val srcRect: Rect
        get() = _srcRect
}

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BackgroundView

Next, create the BackgroundView container for the backscene, which is used to periodically create and move obstacles. Use the barsList to manage all the current obstacles. In onLayout, place the obstacles at the top and bottom of the screen

/** * Backscene container class */
class BackgroundView(context: Context, attrs: AttributeSet?) : FrameLayout(context, attrs) {

    internal val barsList = mutableListOf<Bars>()

    override fun onLayout(changed: Boolean, left: Int, top: Int, right: Int, bottom: Int) {
        barsList.flatMap { listOf(it.up, it.down) }.forEach {
            val w = it.view.measuredWidth
            val h = it.view.measuredHeight
            when (it) {
                is UpBar -> it.view.layout(0.0, w, h)
                else -> it.view.layout(0, height - h, w, height)
            }
        }
    }
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Provide two methods start and stop to control the start and end of the game:

At the end of the game, all obstacles are required to stop moving.
It will pass when the game startsTimerAnd periodically refresh obstacles

    /** * End of game, stop all obstacles */
    @UiThread
    fun stop(a) {
        _timer.cancel()
        _anims.forEach { it.cancel() }
        _anims.clear()
    }

    /** * Periodically refresh obstacles: * 1. Create * 2. Add to view * 3. Mobile * /
    @UiThread
    fun start(a) {
        _clearBars()
        Timer().also { _timer = it }.schedule(object : TimerTask() {
            override fun run(a) {
                post {
                    _createBars(context, barsList.lastOrNull()).let {
                        _addBars(it)
                        _moveBars(it)
                    }
                }
            }

        },  FIRST_APPEAR_DELAY_MILLIS, BAR_APPEAR_INTERVAL_MILLIS
        )
    }

     /** * When the game restarts, clear obstacles */
    private fun _clearBars(a) {
        barsList.clear()
        removeAllViews()
    }

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Refresh obstacles

Obstacle refreshment goes through three steps:

Create: Create an obstacle in a group of two
Add: Adds an object tobarsListAnd at the same time willViewAdd to container
Move: Move from the right to the left by animating properties, and delete after moving off screen

When creating an obstacle, set a random height for it. The randomness should not be too high. Adjust the height based on the previous obstacle to ensure randomness and consistency

    /** * Create an obstacle */
    private fun _createBars(context: Context, pre: Bars?). = run {
        val up = UpBar(context, this).apply { h = pre? .let {val step = when {
                    it.up.h >= height - _gap - _step -> -_step
                    it.up.h <= _step -> _step
                    _random.nextBoolean() -> _step
                    else-> -_step } it.up.h + step } ? : _barHeight w = _barWidth }val down = DnBar(context, this).apply {
            h = height - up.h - _gap
            w = _barWidth
        }

        Bars(up, down)

    }

    /** * add to screen */
    private fun _addBars(bars: Bars) {
        barsList.add(bars)
        bars.asArray().forEach {
            addView(
                it.view,
                ViewGroup.LayoutParams(
                    it.w.toInt(),
                    it.h.toInt()
                )
            )
        }
    }

    /** * Use properties to animate obstacles */
    private fun _moveBars(bars: Bars) {
        _anims.add(
            ValueAnimator.ofFloat(width.toFloat(), -_barWidth)
                .apply {
                    addUpdateListener {
                        bars.asArray().forEach { bar ->
                            bar.x = it.animatedValue as Float
                            if (bar.x + bar.w <= 0) { post { removeView(bar.view) } } } } duration = BAR_MOVE_DURATION_MILLIS interpolator = LinearInterpolator() start() }}})Copy the code

Foreground

Boat

Class Boat, creates a custom View, and provides methods to move to the specified coordinates

/** * sub */
class Boat(context: Context) {

    internal val view by lazy { BoatView(context) }

    val h
        get() = view.height.toFloat()

    val w
        get() = view.width.toFloat()

    val x
        get() = view.x

    val y
        get() = view.y

    /** * moves to the specified coordinate */
    fun moveTo(x: Int, y: Int) {
        view.smoothMoveTo(x, y)
    }

}

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BoatView

The following things are done in a custom View

Two resources are switched periodically to achieve the effect of searchlight flashing
throughOverScrollerMake the movement smoother
Through aRotation Animation, allowing the submarine to turn the Angle when moving, more flexible

internal class BoatView(context: Context?) : AppCompatImageView(context) {

    private val _scroller by lazy { OverScroller(context) }

    private val _res = arrayOf(
        R.mipmap.boat_000,
        R.mipmap.boat_002
    )

    private var _rotationAnimator: ObjectAnimator? = null

    private var _cnt = 0
        set(value) {
            field = if (value > 1) 0 else value
        }

    init {
        scaleType = ScaleType.FIT_CENTER
        _startFlashing()
    }

    private fun _startFlashing(a) {
        postDelayed({
            setImageResource(_res[_cnt++])
            _startFlashing()
        }, 500)}override fun computeScroll(a) {
        super.computeScroll()

        if (_scroller.computeScrollOffset()) {

            x = _scroller.currX.toFloat()
            y = _scroller.currY.toFloat()

            // Keep on drawing until the animation has finished.
            postInvalidateOnAnimation()
        }

    }

    /** * moves more smoothly */
    internal fun smoothMoveTo(x: Int, y: Int) {
        if(! _scroller.isFinished) _scroller.abortAnimation() _rotationAnimator? .let {if (it.isRunning) it.cancel() }

        val curX = this.x.toInt()
        val curY = this.y.toInt()

        val dx = (x - curX)
        val dy = (y - curY)
        _scroller.startScroll(curX, curY, dx, dy, 250)

        _rotationAnimator = ObjectAnimator.ofFloat(
            this."rotation",
            rotation,
            Math.toDegrees(atan((dy / 100.toDouble()))).toFloat()
        ).apply {
            duration = 100
            start()
        }

        postInvalidateOnAnimation()
    }
}
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ForegroundView

throughboatMembers hold and control submarine objects
implementationCameraHelper.FaceDetectListenerAccording to the face recognition callback, move the submarine to the specified position
At the start of the game, build the submarine and do the opening animation


/** * foreground container class */
class ForegroundView(context: Context, attrs: AttributeSet?) : FrameLayout(context, attrs),
    CameraHelper.FaceDetectListener {

    private var _isStop: Boolean = false

    internal var boat: Boat? = null

    /** * The game stops and the sub no longer moves */
    @MainThread
    fun stop(a) {
        _isStop = true
    }
    
    /** * accept face recognition callback, move position */
    override fun onFaceDetect(faces: Array<Face>, facesRect: ArrayList<RectF>) {
        if (_isStop) return
        if(facesRect.isNotEmpty()) { boat? .run {val face = facesRect.first()
                val x = (face.left - _widthOffset).toInt()
                val y = (face.top + _heightOffset).toInt()
                moveTo(x, y)
            }
            _face = facesRect.first()
        }
    }

}

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intro

The game begins by animating the submarine to its starting position, halfway down the Y axis

 /** * The game starts with an animation to enter */
    @MainThread
    fun start(a) {
        _isStop = false
        if (boat == null) {
            boat = Boat(context).also {
                post {
                    addView(it.view, _width, _width)
                    AnimatorSet().apply {
                        play(
                            ObjectAnimator.ofFloat(
                                it.view,
                                "y".0F.this@ForegroundView.height / 2f
                            )
                        ).with(
                            ObjectAnimator.ofFloat(it.view, "rotation".0F.360F)
                        )
                        doOnEnd { _ -> it.view.rotation = 0F }
                        duration = 1000
                    }.start()
                }
            }
        }
    }
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Camera

The camera part mainly consists of TextureView and CameraHelper. TextureView provides Camera bearing preview; CameraHelper implements the following functions:

Turn on the camera: YesCameraMangerAlternate camera
Camera switching: Switch the front and rear cameras.
Preview: Obtain the preview size provided by the Camera and adapt itTextureViewAccording to
Face recognition: detection of face position, forTestureViewThe transformation of coordinates on

Adapter PreviewSize

The previewable size provided by the camera hardware may be different from the actual screen size (i.e. TextureView size), so you need to select the most appropriate PreviewSize during camera initialization to avoid stretching and other exceptions on TextureView

class CameraHelper(val mActivity: Activity, private val mTextureView: TextureView) {

    private lateinit var mCameraManager: CameraManager
    private var mCameraDevice: CameraDevice? = null
    private var mCameraCaptureSession: CameraCaptureSession? = null

    private var canExchangeCamera = false                                               // Whether the camera can be switched
    private var mFaceDetectMatrix = Matrix()                                            // Face detection coordinate transformation matrix
    private var mFacesRect = ArrayList<RectF>()                                         // Save the face coordinate information
    private var mFaceDetectListener: FaceDetectListener? = null                         // Face detection callback
    private lateinit var mPreviewSize: Size

    /** * initializes */
    private fun initCameraInfo(a) {
        mCameraManager = mActivity.getSystemService(Context.CAMERA_SERVICE) as CameraManager
        val cameraIdList = mCameraManager.cameraIdList
        if (cameraIdList.isEmpty()) {
            mActivity.toast("No cameras available")
            return
        }

        // Get the camera direction
        mCameraSensorOrientation =
            mCameraCharacteristics.get(CameraCharacteristics.SENSOR_ORIENTATION)!!
        // Get StreamConfigurationMap, which manages all output formats and sizes supported by the camera
        val configurationMap =
            mCameraCharacteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP)!!

        val previewSize = configurationMap.getOutputSizes(SurfaceTexture::class.java) // Preview the size

        // When the screen is vertical, switch the width and height to make sure that the width is larger than the height
        mPreviewSize = getBestSize(
            mTextureView.height,
            mTextureView.width,
            previewSize.toList()
        )

        // Set TextureView according to the preview size
        mTextureView.surfaceTexture.setDefaultBufferSize(mPreviewSize.width, mPreviewSize.height)
        mTextureView.setAspectRatio(mPreviewSize.height, mPreviewSize.width)
    }

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The principles for selecting preview dimensions should be consistent with the aspect ratio of TextureView, and the area should be as close as possible.

private fun getBestSize(
        targetWidth: Int,
        targetHeight: Int,
        sizeList: List<Size>): Size {
        val bigEnough = ArrayList<Size>()     // A list of sizes larger than the specified width
        val notBigEnough = ArrayList<Size>()  // A list of sizes smaller than the specified width and height

        for (size in sizeList) {

            // Aspect ratio == Target aspect ratio
            if (size.width == size.height * targetWidth / targetHeight
            ) {
                if (size.width >= targetWidth && size.height >= targetHeight)
                    bigEnough.add(size)
                else
                    notBigEnough.add(size)
            }
        }

        // Select the smallest value in bigEnough or the largest value in notBigEnough
        return when {
            bigEnough.size > 0 -> Collections.min(bigEnough, CompareSizesByArea())
            notBigEnough.size > 0 -> Collections.max(notBigEnough, CompareSizesByArea())
            else -> sizeList[0]
        }
		
		initFaceDetect()
    }
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InitFaceDetect () is used to initialize the Matrix of the face, described below

Face recognition

As the camera preview, create a CameraCaptureSession object, session through CameraCaptureSession. Return to TotalCaptureResult CaptureCallback, through the parameters including can face recognition of relevant information

 /** * Create a preview session */
    private fun createCaptureSession(cameraDevice: CameraDevice) {

        // Create a CameraCaptureSession object for camera preview
        cameraDevice.createCaptureSession(
            arrayListOf(surface),
            object : CameraCaptureSession.StateCallback() {

                override fun onConfigured(session: CameraCaptureSession) {
                    mCameraCaptureSession = session
                    session.setRepeatingRequest(
                        captureRequestBuilder.build(),
                        mCaptureCallBack,
                        mCameraHandler
                    )
                }

            },
            mCameraHandler
        )
    }

    private val mCaptureCallBack = object : CameraCaptureSession.CaptureCallback() {
        override fun onCaptureCompleted(
            session: CameraCaptureSession,
            request: CaptureRequest,
            result: TotalCaptureResult
        ) {
            super.onCaptureCompleted(session, request, result)
            if(mFaceDetectMode ! = CaptureRequest.STATISTICS_FACE_DETECT_MODE_OFF) handleFaces(result) } }Copy the code

MFaceDetectMatrix is used to change the matrix of face information and determine the face coordinates to make it accurately applied to TextureView.

  /** ** Handle face information */
    private fun handleFaces(result: TotalCaptureResult) {
        val faces = result.get(CaptureResult.STATISTICS_FACES)!!
        mFacesRect.clear()

        for (face in faces) {
            val bounds = face.bounds

            val left = bounds.left
            val top = bounds.top
            val right = bounds.right
            val bottom = bounds.bottom

            val rawFaceRect =
                RectF(left.toFloat(), top.toFloat(), right.toFloat(), bottom.toFloat())
            mFaceDetectMatrix.mapRect(rawFaceRect)

            var resultFaceRect = if (mCameraFacing == CaptureRequest.LENS_FACING_FRONT) {
                rawFaceRect
            } else {
                RectF(
                    rawFaceRect.left,
                    rawFaceRect.top - mPreviewSize.width,
                    rawFaceRect.right,
                    rawFaceRect.bottom - mPreviewSize.width
                )
            }

            mFacesRect.add(resultFaceRect)

        }
        
  		mActivity.runOnUiThread {
            mFaceDetectListener?.onFaceDetect(faces, mFacesRect)
        }
    }
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Finally, the UI thread passes the Rect containing the face coordinates through a callback:

mActivity.runOnUiThread {
        mFaceDetectListener?.onFaceDetect(faces, mFacesRect)
    }
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FaceDetectMatrix

MFaceDetectMatrix is created after getting PreviewSize


    /** * Initializes face detection information */
    private fun initFaceDetect(a) {

        val faceDetectModes =
            mCameraCharacteristics.get(CameraCharacteristics.STATISTICS_INFO_AVAILABLE_FACE_DETECT_MODES)  // Face detection mode

        mFaceDetectMode = when{ faceDetectModes!! .contains(CaptureRequest.STATISTICS_FACE_DETECT_MODE_FULL) -> CaptureRequest.STATISTICS_FACE_DETECT_MODE_FULL faceDetectModes!! .contains(CaptureRequest.STATISTICS_FACE_DETECT_MODE_SIMPLE) -> CaptureRequest.STATISTICS_FACE_DETECT_MODE_FULLelse -> CaptureRequest.STATISTICS_FACE_DETECT_MODE_OFF
        }

        if (mFaceDetectMode == CaptureRequest.STATISTICS_FACE_DETECT_MODE_OFF) {
            mActivity.toast("Camera hardware does not support face detection.")
            return
        }

        val activeArraySizeRect =
            mCameraCharacteristics.get(CameraCharacteristics.SENSOR_INFO_ACTIVE_ARRAY_SIZE)!! // Get the image area
        val scaledWidth = mPreviewSize.width / activeArraySizeRect.width().toFloat()
        val scaledHeight = mPreviewSize.height / activeArraySizeRect.height().toFloat()

        val mirror = mCameraFacing == CameraCharacteristics.LENS_FACING_FRONT

        mFaceDetectMatrix.setRotate(mCameraSensorOrientation.toFloat())
        mFaceDetectMatrix.postScale(if (mirror) -scaledHeight else scaledHeight, scaledWidth)// Switch width and height!
        mFaceDetectMatrix.postTranslate(
            mPreviewSize.height.toFloat(),
            mPreviewSize.width.toFloat()
        )

    }
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Control class (GameController)

After three view layers are assembled, a master control class is needed to control the game logically

GameController

Mainly completed the following work:

Controls the start/stop of the game
Calculates the current score of the game
Detect submarine collisions
Foreign (ActivityorFragmentEtc.) provides an interface for game state monitoring

Initialize the

The game starts by initializing the camera, creating the GameHelper class and setting up the setFaceDetectListener callback to the ForegroundView

class GameController(
    private val activity: AppCompatActivity,
    private val textureView: AutoFitTextureView,
    private val bg: BackgroundView,
    private val fg: ForegroundView
) {
    
    private var camera2HelperFace: CameraHelper? = null
    /** * Camera initialization */
    private fun initCamera(a){ cameraHelper ? : run { cameraHelper = CameraHelper(activity, textureView).apply { setFaceDetectListener(object : CameraHelper.FaceDetectListener {
                    override fun onFaceDetect(faces: Array<Face>, facesRect: ArrayList<RectF>) {
                        if (facesRect.isNotEmpty()) {
                            fg.onFaceDetect(faces, facesRect)
                        }
                    }
                })
            }
        }
    }


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The game state

Define GameState to provide external status listening. Currently, three states are supported

Start: The game starts
Over: The game is Over
Score: The Score of a game

sealed class GameState(open val score: Long) {
    object Start : GameState(0)
    data class Over(override val score: Long) : GameState(score)
    data class Score(override val score: Long) : GameState(score)
}
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You can update the status at stop and start



    /** * Game state */
    private val _state = MutableLiveData<GameState>()
    internal val gameState: LiveData<GameState>
        get() = _state

    /**
     * 游戏停止
     */
    fun stop(a) {
        bg.stop()
        fg.stop()
        _state.value = GameState.Over(_score)
        _score = 0L
    }

    /** ** start */
    fun start(a) {
        initCamera()
        fg.start()
        bg.start()
        _state.value = GameState.Start
        handler.postDelayed({
            startScoring()
        }, FIRST_APPEAR_DELAY_MILLIS)
    }
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Calculate a score

At the start of the game, startScoring is calculated and reported by GameState. The current rules are simple, with the survival time being the game score

    /**
     * 开始计分
     */
    private fun startScoring(a){ handler.postDelayed( { fg.boat? .run { bg.barsList.flatMap { listOf(it.up, it.down) } .forEach { bar ->if (isCollision(
                                    bar.x, bar.y, bar.w, bar.h,
                                    this.x, this.y, this.w, this.h
                                )
                            ) {
                                stop()
                                return@postDelayed
                            }
                        }
                }
                _score++
                _state.value = GameState.Score(_score)
                startScoring()
            }, 100)}Copy the code

Collision detection

IsCollision calculates whether a collision has occurred according to the current position of the submarine and obstacle, and GameOver occurs when a collision occurs

  /** * Collision detection */
    private fun isCollision(
        x1: Float,
        y1: Float,
        w1: Float,
        h1: Float,
        x2: Float,
        y2: Float,
        w2: Float,
        h2: Float
    ): Boolean {
        if (x1 > x2 + w2 || x1 + w1 < x2 || y1 > y2 + h2 || y1 + h1 < y2) {
            return false
        }
        return true
    }
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Activity

The Activity works simply:

Permission application: Dynamically apply for Camera permission
Listen for GameState: create a GameController and listen for the GameState state

    private fun startGame(a) {
        PermissionUtils.checkPermission(this, Runnable {
            gameController.start()
            gameController.gameState.observe(this, Observer {
                when (it) {
                    is GameState.Start ->
                        score.text = "DANGER\nAHEAD"
                    is GameState.Score ->
                        score.text = "${it.score / 10f} m"
                    is GameState.Over ->
                        AlertDialog.Builder(this)
                            .setMessage("Game over! Successfully promote${it.score / 10f}Meters! ")
                            .setNegativeButton("End the game.") { _: DialogInterface, _: Int ->
                                finish()
                            }.setCancelable(false)
                            .setPositiveButton("Give me one more.") { _: DialogInterface, _: Int ->
                                gameController.start()
                            }.show()
                }
            })
        })
    }
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The last

The structure of the project is very clear, and most of the use of conventional technology, even for the new Android students look effortless. The game can be further improved by adding BGM and obstacle types. If you like, leave a star to encourage the author ^^

Github.com/vitaviva/ug…

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【Android】 Hand lift douyin small game submarine big challenge

The basic idea

Background

Bar

BackgroundView

Refresh obstacles

Foreground

Boat

BoatView

ForegroundView

intro

Camera

Adapter PreviewSize

Face recognition

FaceDetectMatrix

Control class (GameController)

GameController

Initialize the

The game state

Calculate a score

Collision detection

Activity

The last

【Android】 Hand lift douyin small game submarine big challenge

The basic idea

Background

Bar

BackgroundView

Refresh obstacles

Foreground

Boat

BoatView

ForegroundView

intro

Camera

Adapter PreviewSize

Face recognition

FaceDetectMatrix

Control class (GameController)

GameController

Initialize the

The game state

Calculate a score

Collision detection

Activity

The last

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