title: How to draw lines on OpenCV Camera Preview?
body: <p>Im using OpenCV camera preview.</p>
  
  <p>I want to draw a rectangle over the live preview.
  Ive tried to override the ondraw method, but I cant see a line.
  Please help.</p>
  
  <pre><code>package com.example.easymeasure;
  
  import org.opencv.android.JavaCameraView;
  
  import android.content.Context;
  import android.content.res.Resources;
  import android.graphics.Canvas;
  import android.graphics.Paint;
  import android.util.AttributeSet;
  
  public class CustomOpenCVJavaCameraView extends JavaCameraView {
  
      public CustomOpenCVJavaCameraView(Context context, AttributeSet attrs) {
          super(context, attrs);
          init();
      }
  
      private Paint linePaint;
      protected void init() { 
          Resources r = this.getResources();
          linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
          linePaint.setAlpha(200);
          linePaint.setStrokeWidth(1);
          linePaint.setStyle(Paint.Style.STROKE);
          linePaint.setColor(r.getColor(R.color.marker_color));
          linePaint.setShadowLayer(2, 1, 1, r.getColor(R.color.shadow_color));        
      }
  
      @Override
        protected void onDraw(Canvas canvas) {
          super.onDraw(canvas);       
          linePaint.setStrokeWidth(5);
          canvas.drawLine(10,20,1000,200,linePaint);
      }
  }
  </code></pre>