c# - 如何使用 Xamarin.Android 在相机流上绘制标记？

Question

我设法在 TextureView 上显示相机流，并制作一个位图来读取流中每一帧的像素。然后我可以应用跟踪算法来跟踪一个球。但是现在，我想显示一个红色标记(例如)，它显示找到的球的位置。我该怎么做？

Answer 1

我相信有很多方法可以在相机 View 上绘制标记。这里我使用了一个SurfaceView。基本思想是在 Textureview 的顶部设置一个具有透明背景的 SurfaceView。

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

  <TextureView android:id="@+id/textureView"
               android:layout_height="match_parent"
               android:layout_width="match_parent" />

  <SurfaceView
        android:id="@+id/surfaceview"
        android:layout_height="match_parent"
        android:layout_width="match_parent" />
</RelativeLayout >

代码隐藏:

public class MainActivity : Activity, TextureView.ISurfaceTextureListener
{
    private Android.Hardware.Camera _camera;
    private TextureView _textureView;
    private SurfaceView _surfaceView;
    private ISurfaceHolder holder;

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.Main);

        _textureView = (TextureView)FindViewById(Resource.Id.textureView);
        _textureView.SurfaceTextureListener = this;

        _surfaceView = (SurfaceView)FindViewById(Resource.Id.surfaceview);
        //set to top layer
        _surfaceView.SetZOrderOnTop(true);
        //set the background to transparent
        _surfaceView.Holder.SetFormat(Format.Transparent);
        holder = _surfaceView.Holder;
        _surfaceView.Touch += _surfaceView_Touch;
    }

    private void _surfaceView_Touch(object sender, View.TouchEventArgs e)
    {
        //define the paintbrush
        Paint mpaint = new Paint();
        mpaint.Color = Color.Red;
        mpaint.SetStyle(Paint.Style.Stroke);
        mpaint.StrokeWidth = 2f;

        //draw
        Canvas canvas = holder.LockCanvas();
        //clear the paint of last time
        canvas.DrawColor(Color.Transparent, PorterDuff.Mode.Clear);
        //draw a new one, set your ball's position to the rect here
        var x = e.Event.GetX();
        var y = e.Event.GetY();
        Rect r = new Rect((int)x, (int)y, (int)x + 100, (int)y + 100);
        canvas.DrawRect(r, mpaint);
        holder.UnlockCanvasAndPost(canvas);
    }

    public bool OnSurfaceTextureDestroyed(SurfaceTexture surface)
    {
        _camera.StopPreview();
        _camera.Release();

        return true;
    }

    public void OnSurfaceTextureAvailable(SurfaceTexture surface, int width, int height)
    {
        _camera = Android.Hardware.Camera.Open();

        try
        {
            _camera.SetPreviewTexture(surface);
            _camera.SetDisplayOrientation(90);
            _camera.StartPreview();
        }
        catch (Java.IO.IOException ex)
        {
            Console.WriteLine(ex.Message);
        }
    }

    public void OnSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height)
    {
    }

    public void OnSurfaceTextureUpdated(SurfaceTexture surface)
    {
    }
}

因为我没有跟踪球的跟踪算法，我使用了 SurfaceView 的 Touch 事件，每次当你点击 SurfaceView，点击的位置会绘制一个红色描边的矩形。您可以将我的_surfaceView_Touch 方法中的代码修改为您的跟踪算法并绘制您的红色标记。