This problem is not difficult. When triggering the drawing of drawing board A, you have to invert the coordinates of point A. According to the conversion relationship, calculate the coordinates of point B and draw the points in B. https://segmentfault.com/n/1330000005040693

MainActivity
 
package com.cyrus.demoboard;
 
import android.app.Activity;
import android.os.Bundle;
import android.view.ViewTreeObserver.OnGlobalLayoutListener;
 
import com.cyrus.demoboard.BoardView.OnPositionListener;
 
 
/**

1. class MainActivity extends Activity {

   
      private BoardView aView;
      private BoardViewB bView;
      
      
      private int wA,hA;
      private int wB,hB;
      
      private float sX = 0.0f;
      private float sY = 0.0f;
      
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          aView = (BoardView)findViewById(R.id.a_boardview);
          bView = (BoardViewB)findViewById(R.id.b_boardview);
          
          aView.getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
              
              @Override
              public void onGlobalLayout() {
                  // TODO Auto-generated method stub
                  hA = aView.getHeight();
                  wA = aView.getWidth();
              }
          });
          
          bView.getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
              
              @Override
              public void onGlobalLayout() {
                  // TODO Auto-generated method stub
                  hB = bView.getHeight();
                  wB = bView.getWidth();
              }
          });
          
          aView.setOnPositionListener(new OnPositionListener() {
              
              @Override
              public void onPositionListener(float x,float y,int action) {
                  // TODO Auto-generated method stub
                  if (sX == 0 || sY == 0) {
                      sX = (wB*1.0f)/wA;
                      sY = (hB*1.0f)/hA;
                  }
                  bView.triggerDraw(x*sX,y*sY,action);
              }
          });
          
      }

   }

   Board A

2. com.cyrus.demoboard;

3. android.annotation.SuppressLint;

4. android.content.Context;

5. android.graphics.Canvas;

6. android.graphics.Paint;

7. android.graphics.Path;

8. android.util.AttributeSet;

9. android.view.MotionEvent;

10. android.view.View;
    /**

    • @author CyrusCao
      *
      */

11. class BoardView extends View {

       
       
       private float mX, mY;
       private Path mPath;
       private static final float TOUCH_TOLERANCE = 4;
       private Paint mPaint;
       private OnPositionListener mPositionListener;
    
       @SuppressLint("NewApi")
       public BoardView(Context context, AttributeSet attrs, int defStyleAttr,
               int defStyleRes) {
           super(context, attrs, defStyleAttr, defStyleRes);
           // TODO Auto-generated constructor stub
           initPaint();
       }
    
       public BoardView(Context context, AttributeSet attrs, int defStyleAttr) {
           super(context, attrs, defStyleAttr);
           // TODO Auto-generated constructor stub
           initPaint();
       }
    
       public BoardView(Context context, AttributeSet attrs) {
           super(context, attrs);
           // TODO Auto-generated constructor stub
           initPaint();
       }
    
       public BoardView(Context context) {
           super(context);
           // TODO Auto-generated constructor stub
           initPaint();
       }
       
       public void initPaint(){
           
           mPaint = new Paint();
           mPaint.setAntiAlias(true);
           mPaint.setDither(true);
           mPaint.setColor(0xFF00FF00);
           mPaint.setStyle(Paint.Style.STROKE);
           mPaint.setStrokeJoin(Paint.Join.ROUND);
           mPaint.setStrokeCap(Paint.Cap.ROUND);
           mPaint.setStrokeWidth(10);  
           
       }
    
       @SuppressLint("ClickableViewAccessibility")
       @Override
       public boolean onTouchEvent(MotionEvent event) {
           // TODO Auto-generated method stub
           float x = event.getX();
           float y = event.getY();
           if (mPositionListener != null) {
               mPositionListener.onPositionListener(x, y,event.getAction());
           }
           switch (event.getAction()) {
               case MotionEvent.ACTION_DOWN:
                   mPath = new Path();
                   touchStart(x, y);
                   break;
               case MotionEvent.ACTION_MOVE:
                   touchMove(x, y);
                   break;
               case MotionEvent.ACTION_UP:
                   touchUp();
                   break;
           }
           invalidate();
           return true;
       }
       
    
    
       @Override
       protected void onDraw(Canvas canvas) {
           // TODO Auto-generated method stub
           if (mPath != null) {
               canvas.drawPath(mPath, mPaint);
           }
       }
       
       private void touchStart(float x, float y) {
           mPath.reset();
           mPath.moveTo(x, y);
           mX = x;
           mY = y;
       }
       private void touchMove(float x, float y) {
           float dx = Math.abs(x - mX);
           float dy = Math.abs(y - mY);
           if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
                mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
               mX = x;
               mY = y;
           }
       }
       private void touchUp() {
           mPath.lineTo(mX, mY);
           mPath = null;
           
       }
       
       
       
       public void setOnPositionListener(OnPositionListener mPositionListener) {
           this.mPositionListener = mPositionListener;
       }
    
       public interface OnPositionListener {
           void onPositionListener(float x,float y,int action);
       }
       
    

    }

    Board B

12. com.cyrus.demoboard;

13. android.annotation.SuppressLint;

14. android.content.Context;

15. android.graphics.Canvas;

16. android.graphics.Paint;

17. android.graphics.Path;

18. android.util.AttributeSet;

19. android.view.MotionEvent;

20. android.view.View;

    /**

    • @author CyrusCao
      *
      */

21. class BoardViewB extends View {

    
       private float mX, mY;
       private Path mPath;
       private static final float TOUCH_TOLERANCE = 4;
       private Paint mPaint;
    
       @SuppressLint("NewApi")
       public BoardViewB(Context context, AttributeSet attrs, int defStyleAttr,
               int defStyleRes) {
           super(context, attrs, defStyleAttr, defStyleRes);
           // TODO Auto-generated constructor stub
           initPaint();
       }
    
       public BoardViewB(Context context, AttributeSet attrs, int defStyleAttr) {
           super(context, attrs, defStyleAttr);
           // TODO Auto-generated constructor stub
           initPaint();
       }
    
       public BoardViewB(Context context, AttributeSet attrs) {
           super(context, attrs);
           // TODO Auto-generated constructor stub
           initPaint();
       }
    
       public BoardViewB(Context context) {
           super(context);
           // TODO Auto-generated constructor stub
           initPaint();
       }
    
       public void initPaint() {
    
           mPaint = new Paint();
           mPaint.setAntiAlias(true);
           mPaint.setDither(true);
           mPaint.setColor(0xFFFF0000);
           mPaint.setStyle(Paint.Style.STROKE);
           mPaint.setStrokeJoin(Paint.Join.ROUND);
           mPaint.setStrokeCap(Paint.Cap.ROUND);
           mPaint.setStrokeWidth(10);
    
       }
    
       public void triggerDraw(float x, float y, int action) {
           switch (action) {
           case MotionEvent.ACTION_DOWN:
               mPath = new Path();
               touchStart(x, y);
               break;
           case MotionEvent.ACTION_MOVE:
               touchMove(x, y);
               break;
           case MotionEvent.ACTION_UP:
               touchUp();
               break;
           }
           invalidate();
       }
    
       @Override
       protected void onDraw(Canvas canvas) {
           // TODO Auto-generated method stub
           if (mPath != null) {
               canvas.drawPath(mPath, mPaint);
           }
       }
    
       private void touchStart(float x, float y) {
           mPath.reset();
           mPath.moveTo(x, y);
           mX = x;
           mY = y;
       }
    
       private void touchMove(float x, float y) {
           float dx = Math.abs(x - mX);
           float dy = Math.abs(y - mY);
           if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
               mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
               mX = x;
               mY = y;
           }
       }
    
       private void touchUp() {
           mPath.lineTo(mX, mY);
           mPath = null;
    
       }
    

    }

22. <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

       xmlns:tools="http://schemas.android.com/tools"
       android:layout_width="match_parent"
       android:layout_height="match_parent" >
    
       <com.cyrus.demoboard.BoardViewB
           android:id="@+id/b_boardview"
           android:layout_width="300dp"
           android:layout_height="250dp"
           android:background="#fff000" />
    
       <com.cyrus.demoboard.BoardView
           android:id="@+id/a_boardview"
           android:layout_width="200dp"
           android:layout_height="200dp"
           android:layout_alignParentBottom="true"
           android:background="#fff000" />
    

    </RelativeLayout>

Websocket can be implemented, but you need to use flash under IE