Android texture view blinking

Question

In the following application the screen is always blinking for some reason, also there are drawing artifacts just above the text. Is it possible to fix this? I am running Android 4.4.2 on a Nexus 7 device.

package com.example.TestSurfaceView;

import android.app.Activity;
import android.graphics.*;
import android.os.Bundle;
import java.util.Random;
import android.os.SystemClock;
import android.view.TextureView;

public class MyActivity extends Activity implements TextureView.SurfaceTextureListener, Runnable {

    TextureView view_;
    Thread thread_;
    long prev_ = -1;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        view_ = new TextureView(this);
        view_.setSurfaceTextureListener(this);
        thread_ = new Thread(this);
        setContentView(view_);
    }

    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
    }

    @Override
    public void run() {
        while(true) {
            Canvas canvas = view_.lockCanvas();
            Paint myPaint = new Paint();
            myPaint.setColor(Color.WHITE);
            myPaint.setStrokeWidth(10);
            canvas.drawRect(100, 100, 300, 300, myPaint);

            Random random = new Random();
            Paint paint = new Paint();
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeWidth(3);

            int w = canvas.getWidth();
            int h = canvas.getHeight();
            int x = random.nextInt(w-1);
            int y = random.nextInt(h-1);
            int r = random.nextInt(255);
            int g = random.nextInt(255);
            int b = random.nextInt(255);
            paint.setColor(0xff000000 + (r << 16) + (g << 8) + b);
            canvas.drawPoint(x, y, paint);

            if(prev_ == -1)
                prev_ = SystemClock.elapsedRealtime();
            else {
                long curr = SystemClock.elapsedRealtime();
                long diff = curr-prev_;
                Paint text = new Paint(Color.WHITE);
                text.setTextSize(15);
                canvas.drawText("FPS: " + String.valueOf(1000.0 / diff), 100, 100, text);
                prev_ = curr;
            }

            view_.unlockCanvasAndPost(canvas);
        }
    }

    @Override
    protected void onPause() {
        // TODO Auto-generated method stub
        super.onPause();
    }

    @Override
    public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture, int i, int i2) {
        thread_.start();
    }

    @Override
    public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture, int i, int i2) {
        //To change body of implemented methods use File | Settings | File Templates.
    }

    @Override
    public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
        return false;  //To change body of implemented methods use File | Settings | File Templates.
    }

    @Override
    public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {
        //To change body of implemented methods use File | Settings | File Templates.
    }
}

Answer 1

Clear the Canvas right after you lock it, e.g. canvas.drawRGB(0,0,0). Otherwise you might pick up artifacts from previous frames.

Answer 2

In my case I need the TextureView to be cleared transparent - the following code did it for me:

  Paint clearPaint = new Paint();
  clearPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));

  while(true) {
      Canvas canvas = surface.lockCanvas(null);
      canvas.drawPaint(clearPaint);
      ...
      surface.unlockCanvasAndPost(canvas);
  }