Face detector (#5)

* Add face detection sample using CameraX + MLKit

* Resize art

* Update README.md

FaceDetectorSample/.gitignore

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+*.iml
+.gradle
+/local.properties
+/.idea/*
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx

FaceDetectorSample/app/.gitignore

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+/build

FaceDetectorSample/app/build.gradle

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+apply plugin: "com.android.application"
+apply plugin: "kotlin-android"
+apply plugin: "kotlin-android-extensions"
+
+android {
+    compileSdkVersion 30
+    buildToolsVersion "29.0.3"
+
+    defaultConfig {
+        applicationId "com.husaynhakeem.facedetectorsample"
+        minSdkVersion 21
+        targetSdkVersion 30
+        versionCode 1
+    }
+
+    // CameraX uses java8 features
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+}
+
+dependencies {
+    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
+    implementation "androidx.core:core-ktx:1.3.0"
+    implementation "androidx.appcompat:appcompat:1.1.0"
+    implementation "androidx.constraintlayout:constraintlayout:1.1.3"
+    implementation "androidx.activity:activity-ktx:1.2.0-alpha06"
+    implementation "androidx.fragment:fragment-ktx:1.3.0-alpha06"
+
+    // CameraX
+    implementation "androidx.camera:camera-camera2:1.0.0-beta06"
+    implementation "androidx.camera:camera-lifecycle:1.0.0-beta06"
+    implementation "androidx.camera:camera-view:1.0.0-alpha13"
+
+    // MLKit
+    implementation "com.google.mlkit:face-detection:16.0.0"
+}

FaceDetectorSample/app/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="com.husaynhakeem.facedetectorsample">
+
+    <!-- For using the camera -->
+    <uses-permission android:name="android.permission.CAMERA" />
+
+    <application
+        android:allowBackup="true"
+        android:label="@string/app_name"
+        android:supportsRtl="true"
+        android:theme="@style/AppTheme">
+        <activity android:name=".MainActivity">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

FaceDetectorSample/app/src/main/java/com/husaynhakeem/facedetectorsample/AnalysisFaceDetector.kt

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+package com.husaynhakeem.facedetectorsample
+
+import android.annotation.SuppressLint
+import android.graphics.Rect
+import android.graphics.RectF
+import androidx.camera.core.ImageAnalysis
+import androidx.camera.core.ImageProxy
+import com.google.mlkit.vision.common.InputImage
+import com.google.mlkit.vision.face.Face
+import com.google.mlkit.vision.face.FaceDetection
+import com.google.mlkit.vision.face.FaceDetector
+
+/** CameraX Analyzer that wraps MLKit's FaceDetector.  */
+internal class AnalysisFaceDetector(
+    private val previewWidth: Int,
+    private val previewHeight: Int,
+    private val isFrontLens: Boolean
+) : ImageAnalysis.Analyzer {
+
+    private val faceDetector: FaceDetector = FaceDetection.getClient()
+
+    /** Listener to receive callbacks for when faces are detected, or an error occurs.  */
+    var listener: Listener? = null
+
+    @SuppressLint("UnsafeExperimentalUsageError")
+    override fun analyze(imageProxy: ImageProxy) {
+        val image = imageProxy.image
+        if (image == null) {
+            imageProxy.close()
+            return
+        }
+
+        val rotation = imageProxy.imageInfo.rotationDegrees
+        val inputImage = InputImage.fromMediaImage(image, rotation)
+        faceDetector
+            .process(inputImage)
+            .addOnSuccessListener { faces: List<Face> ->
+                val listener = listener ?: return@addOnSuccessListener
+
+                // In order to correctly display the face bounds, the orientation of the analyzed
+                // image and that of the viewfinder have to match. Which is why the dimensions of
+                // the analyzed image are reversed if its rotation information is 90 or 270.
+                val reverseDimens = rotation == 90 || rotation == 270
+                val width = if (reverseDimens) imageProxy.height else imageProxy.width
+                val height = if (reverseDimens) imageProxy.width else imageProxy.height
+
+                val faceBounds = faces.map { it.boundingBox.transform(width, height) }
+                listener.onFacesDetected(faceBounds)
+                imageProxy.close()
+            }
+            .addOnFailureListener { exception ->
+                listener?.onError(exception)
+                imageProxy.close()
+            }
+    }
+
+    private fun Rect.transform(width: Int, height: Int): RectF {
+        val scaleX = previewWidth / width.toFloat()
+        val scaleY = previewHeight / height.toFloat()
+
+        // If the front camera lens is being used, reverse the right/left coordinates
+        val flippedLeft = if (isFrontLens) width - right else left
+        val flippedRight = if (isFrontLens) width - left else right
+
+        // Scale all coordinates to match preview
+        val scaledLeft = scaleX * flippedLeft
+        val scaledTop = scaleY * top
+        val scaledRight = scaleX * flippedRight
+        val scaledBottom = scaleY * bottom
+        return RectF(scaledLeft, scaledTop, scaledRight, scaledBottom)
+    }
+
+    /**
+     * Interface to register callbacks for when the face detector provides detected face bounds, or
+     * when it encounters an error.
+     */
+    internal interface Listener {
+        /** Callback that receives face bounds that can be drawn on top of the viewfinder.  */
+        fun onFacesDetected(faceBounds: List<RectF>)
+
+        /** Invoked when an error is encounter during face detection.  */
+        fun onError(exception: Exception)
+    }
+}

FaceDetectorSample/app/src/main/java/com/husaynhakeem/facedetectorsample/CameraViewModel.kt

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+package com.husaynhakeem.facedetectorsample
+
+import android.app.Application
+import androidx.camera.lifecycle.ProcessCameraProvider
+import androidx.core.content.ContextCompat
+import androidx.lifecycle.AndroidViewModel
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MutableLiveData
+import java.util.concurrent.ExecutionException
+
+/** ViewModel that provides a [ProcessCameraProvider] to interact with the camera. */
+class CameraViewModel(application: Application) : AndroidViewModel(application) {
+
+    private val _getProcessCameraProvider by lazy {
+        MutableLiveData<ProcessCameraProvider>().apply {
+            val cameraProviderFuture = ProcessCameraProvider.getInstance(getApplication())
+            cameraProviderFuture.addListener(
+                Runnable {
+                    try {
+                        value = cameraProviderFuture.get()
+                    } catch (exception: ExecutionException) {
+                        throw IllegalStateException(
+                            "Failed to retrieve a ProcessCameraProvider instance", exception
+                        )
+                    } catch (exception: InterruptedException) {
+                        throw IllegalStateException(
+                            "Failed to retrieve a ProcessCameraProvider instance", exception
+                        )
+                    }
+                },
+                ContextCompat.getMainExecutor(getApplication())
+            )
+        }
+    }
+    val processCameraProvider: LiveData<ProcessCameraProvider>
+        get() = _getProcessCameraProvider
+}

FaceDetectorSample/app/src/main/java/com/husaynhakeem/facedetectorsample/FaceBoundsOverlay.kt

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+package com.husaynhakeem.facedetectorsample
+
+import android.content.Context
+import android.graphics.Canvas
+import android.graphics.Paint
+import android.graphics.RectF
+import android.util.AttributeSet
+import android.view.View
+import androidx.core.content.ContextCompat
+
+/** Overlay where face bounds are drawn.  */
+class FaceBoundsOverlay constructor(context: Context?, attributeSet: AttributeSet?) :
+    View(context, attributeSet) {
+
+    private val faceBounds: MutableList<RectF> = mutableListOf()
+    private val paint = Paint().apply {
+        style = Paint.Style.STROKE
+        color = ContextCompat.getColor(context!!, android.R.color.black)
+        strokeWidth = 10f
+    }
+
+    override fun onDraw(canvas: Canvas) {
+        super.onDraw(canvas)
+        faceBounds.forEach { canvas.drawRect(it, paint) }
+    }
+
+    fun drawFaceBounds(faceBounds: List<RectF>) {
+        this.faceBounds.clear()
+        this.faceBounds.addAll(faceBounds)
+        invalidate()
+    }
+}