@Override
 public void onDrawFrame(GL10 unused) {
   GLES20.glViewport(0, 0, screenWidth, screenHeight);
   GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
   synchronized (yuvImageRenderers) {
     for (YuvImageRenderer yuvImageRenderer : yuvImageRenderers) {
       yuvImageRenderer.draw(drawer);
     }
   }
 }