Veja a seguinte imagem

Eu quero mudar a forma de exibição destacada, arrastando o seu canto .. não é necessário a visão depois de arrastar o canto deve ser retângulo pode ser qualquer forma arbitrária

como conseguir isso?

agora eu fiz os 4 cantos móveis no evento de toque, mas a forma não está mudando

<code>package com.assignment.DragDrop;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;

public class DrawView extends View {


    Point point1,point2,point3,point4;
    private ColorBall[] colorballs = new ColorBall[4]; // array that holds the balls
    private int balID = 0; // variable to know what ball is being dragged
    Paint paint;
    Canvas canvas;
    public DrawView(Context context) {
        super(context);
         paint=new Paint();
        setFocusable(true); //necessary for getting the touch events
        canvas= new Canvas();
        // setting the start point for the balls
        point1 = new Point();
        point1.x = 50;
        point1.y = 20;

        point2 = new Point();
        point2.x = 150;
        point2.y = 20;

        point3 = new Point();
        point3.x = 150;
        point3.y = 120;

        point4 = new Point();
        point4.x = 50;
        point4.y = 120;


        // declare each ball with the ColorBall class
        colorballs[0] = new ColorBall(context,R.drawable.bol_blauw, point1);
        colorballs[1] = new ColorBall(context,R.drawable.bol_blauw, point2);
        colorballs[2] = new ColorBall(context,R.drawable.bol_groen, point3);
        colorballs[3] = new ColorBall(context,R.drawable.bol_geel, point4);


    }

    // the method that draws the balls
    @Override protected void onDraw(Canvas canvas) {
        //canvas.drawColor(0xFFCCCCCC);     //if you want another background color       

        paint.setAntiAlias(true);
        paint.setDither(true);
        paint.setColor(Color.BLACK);
        paint.setStyle(Paint.Style.FILL);
        paint.setStrokeJoin(Paint.Join.ROUND);
       // mPaint.setStrokeCap(Paint.Cap.ROUND);
        paint.setStrokeWidth(5);


          canvas.drawPaint(paint);
          paint.setColor(Color.WHITE);

          canvas.drawRect(point1.x+25, point2.x, point3.x+25, point4.x, paint);
          BitmapDrawable mBitmap;
          mBitmap= new BitmapDrawable();

        //  canvas.drawBitmap(bitmap, left, top, paint)
        // shade_region_between_points();
         // canvas.drawLine(point1.x, point1.y, point2.x, point2.y, paint);
        //  canvas.drawLine(point1.x, point1.y, point4.x, point4.y, paint);

        //  canvas.drawLine(point4.x, point4.y, point3.x, point3.y, paint);
        // canvas.drawLine(point2.x, point2.y, point3.x, point3.y, paint);
          //draw the balls on the canvas
        for (ColorBall ball : colorballs) {
            canvas.drawBitmap(ball.getBitmap(), ball.getX(), ball.getY(), paint);
             // canvas.drawLine(point1.x, point1.y, point2.x, point2.y, paint);

    //  canvas.drawRect(point1.x, point2.x, point3.x, point4.x, paint);



        }
        /*Drawable drawable = getResources().getDrawable(R.drawable.ic_launcher);
        drawable.setBounds( point1.x+25, point2.x, point3.x+25, point4.x);
        drawable.draw(canvas);*/
    }

    // events when touching the screen
    public boolean onTouchEvent(MotionEvent event) {
        int eventaction = event.getAction(); 

        int X = (int)event.getX(); 
        int Y = (int)event.getY(); 

        switch (eventaction ) { 

        case MotionEvent.ACTION_DOWN: // touch down so check if the finger is on a ball
            balID = 0;
            for (ColorBall ball : colorballs) {
                // check if inside the bounds of the ball (circle)
                // get the center for the ball
                int centerX = ball.getX() + 25;
                int centerY = ball.getY() + 25;
                paint.setColor(Color.CYAN);
                // calculate the radius from the touch to the center of the ball
                double radCircle  = Math.sqrt( (double) (((centerX-X)*(centerX-X)) + (centerY-Y)*(centerY-Y)));
                //  canvas.drawLine(point1.x, point1.y, point2.x, point2.y, paint);

                // if the radius is smaller then 23 (radius of a ball is 22), then it must be on the ball
                if (radCircle < 23){

                    balID = ball.getID();
                    canvas.drawRect(point1.x, point2.x, point3.x, point4.x, paint);

                    invalidate(); 
                    break;
                }
                invalidate(); 

                //canvas.drawRect(point1.x, point2.x, point3.x, point4.x, paint);
                // check all the bounds of the ball (square)
                //if (X > ball.getX() && X < ball.getX()+50 && Y > ball.getY() && Y < ball.getY()+50){
                //  balID = ball.getID();
                //  break;
                //}
            }

            break; 


        case MotionEvent.ACTION_MOVE:   // touch drag with the ball
            // move the balls the same as the finger
            if (balID > 0) {
            try {
                colorballs[balID-1].setX(X-25);
                    colorballs[balID-1].setY(Y-25);
                     // canvas.drawLine(point1.x, point1.y, point2.x, point2.y, paint);

            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            paint.setColor(Color.CYAN);
            canvas.drawRect(point1.x, point2.x, point3.x, point4.x, paint);
            invalidate(); 
            }

            break; 

        case MotionEvent.ACTION_UP: 
            // touch drop - just do things here after dropping

            break; 
        } 
        // redraw the canvas
        invalidate(); 
        return true; 

    }


    public void shade_region_between_points()
    {
        canvas.drawRect(point1.x, point2.x, point3.x, point4.x, paint);
    }
}
</code>

Eu peguei esse código da internet.

isso será capaz de mover cantos no evento de toque, mas a forma não está se movendo ...