在相机预览上绘制矩形

Question

我有一个相机预览，其中我获取每一帧，对于每一帧我分析内部的对象并且我有一个包含每个识别的对象和位置的列表，所以我已经有了每个对象的位置。现在我想在相机预览中围绕该对象绘制一个矩形，但是 canvas.drawRect 不起作用，有什么建议吗？

                for (final Detector.Recognition result : results) {
                final RectF location = result.getLocation();
                if (location != null && result.getConfidence() >= 0.1) {
                    result.setLocation(location);
                    mappedRecognitions.add(result);
                    Log.d("OBJECT: ", result.getTitle());

                    final Paint paint = new Paint();
                    paint.setColor(Color.RED);
                    paint.setStyle(Paint.Style.STROKE);
                    paint.setStrokeWidth(2.0f);
                    canvas_crop.drawRect(location, paint);
                    cropToFrameTransform.mapRect(location);
                }
            }

这是布局XML

<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/black"
    android:orientation="vertical">


    <FrameLayout
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </FrameLayout>

    <com.otaliastudios.cameraview.CameraView
        android:id="@+id/cameraView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</RelativeLayout>


</androidx.coordinatorlayout.widget.CoordinatorLayout>

Answer 1

如果你不需要记录矩形，所以只在实时预览中显示，那么一般的解决方案是覆盖一个专门用于绘图渲染的自定义视图。

创建一个自定义视图并将其放在顶部，确保它始终匹配 CameraView 显示的预览的位置和大小（纵横比）。接下来是一个让您入门的示例，尽管您需要添加逻辑以确保它与 CameraView "preview" 指标匹配。使用 setTargets 将矩形传递给绘画：

Java:

public final class OverlayView extends View {
    private final Paint paint = new Paint();
    private final List<Rect> targets = new ArrayList<>();

    public OverlayView(@NonNull final Context context) {
        this(context, null);
    }

    public OverlayView(@NonNull final Context context, @Nullable final AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public OverlayView(@NonNull final Context context, @Nullable final AttributeSet attrs, final int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        final float density = context.getResources().getDisplayMetrics().density;
        this.paint.setStrokeWidth(2.0f * density);
        this.paint.setColor(Color.BLUE);
        this.paint.setStyle(Paint.Style.STROKE);
    }

    @Override
    protected void onDraw(final Canvas canvas) {
        super.onDraw(canvas);

        synchronized (this) {
            for (final Rect entry : this.targets) {
                canvas.drawRect(entry, this.paint);
            }
        }
    }

    public void setTargets(@NonNull final List<Rect> sources) {
        synchronized (this) {
            this.targets.clear();
            this.targets.addAll(sources);
            this.postInvalidate();
        }
    }
}

科特林：

class OverlayView(context: Context, attrs: AttributeSet) : View(context, attrs) {
    private val paint = Paint()
    private val targets: MutableList<Rect> = ArrayList()

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)

        synchronized(this) {
            for (entry in targets) {
                canvas.drawRect(entry, paint)
            }
        }
    }

    fun setTargets(sources: List<Rect>) {
        synchronized(this) {
            targets.clear()
            targets.addAll(sources)
            this.postInvalidate()
        }
    }

    init {
        val density = context.resources.displayMetrics.density
        paint.strokeWidth = 2.0f * density
        paint.color = Color.BLUE
        paint.style = Paint.Style.STROKE
    }
}

对于您的特定 xml，将如下所示：

<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/black"
    android:orientation="vertical">


    <FrameLayout
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </FrameLayout>

    <com.otaliastudios.cameraview.CameraView
        android:id="@+id/cameraView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
        
    <com.otaliastudios.cameraview.OverlayView 
        android:id="@+id/overlayView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
        
</RelativeLayout>


</androidx.coordinatorlayout.widget.CoordinatorLayout>

请注意，您正在为 CameraView 使用 match_parent，这应该在代码中更好地处理以适应所有可能的相机宽高比，因此当您解决预览大小，这也必须应用于新的 OverlayView.

在相机预览上绘制矩形

Draw rect over camera preview

java

android

canvas

drawrect