Question

I need to draw a circle as per my finger move so i have write this code

package com.sport;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.BlurMaskFilter;
import android.graphics.BlurMaskFilter.Blur;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff.Mode;
import android.graphics.PorterDuffXfermode;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Toast;

public class sport extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new TouchView(this));

    }

    class TouchView extends View {
        Bitmap bgr;
        Bitmap overlayDefault;
        Bitmap overlay;
        Paint pTouch;

        int X;
        int Y;
        Canvas c2;

        public TouchView(Context context) {
            super(context);

            bgr = BitmapFactory.decodeResource(getResources(), R.drawable.new1);
            overlayDefault = BitmapFactory.decodeResource(getResources(),
                    R.drawable.original);
            overlay = BitmapFactory.decodeResource(getResources(),
                    R.drawable.new1).copy(Config.ARGB_8888, true);
            c2 = new Canvas(overlay);

            pTouch = new Paint(Paint.DEV_KERN_TEXT_FLAG);
            pTouch.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
            pTouch.setColor(Color.TRANSPARENT);
            // pTouch.setMaskFilter(new BlurMaskFilter(15, Blur.NORMAL));
            DisplayMetrics displaymetrics = new DisplayMetrics();
            getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
            int ht = displaymetrics.heightPixels;
            int wt = displaymetrics.widthPixels;

            X = wt / 2;
            Y = 0;

        }

        @Override
        public boolean onTouchEvent(MotionEvent ev) {

            switch (ev.getAction()) {

            case MotionEvent.ACTION_DOWN: {

                X = (int) ev.getX();
                Y = (int) ev.getY();
                //invalidate();

                break;
            }

            case MotionEvent.ACTION_MOVE: {

                X = (int) ev.getX();
                Y = (int) ev.getY();
                /* Toast.makeText(getBaseContext(),"x is::"+ X,
                          Toast.LENGTH_LONG).show();
                          Toast.makeText(getBaseContext(),"Y is::"+ Y,
                         Toast.LENGTH_LONG).show();*/
                          //c2.drawCircle(X, Y, 70, pTouch);

                /*System.out.println("x is"+X);
                System.out.println("Y is"+Y);*/
                invalidate();
                break;

            }

            case MotionEvent.ACTION_UP:
                X = (int) ev.getX();
                Y = (int) ev.getY();
                /*
                 * Toast.makeText(getBaseContext(),"x is::"+ X,
                 * Toast.LENGTH_LONG).show();
                 * Toast.makeText(getBaseContext(),"Y is::"+ Y,
                 * Toast.LENGTH_LONG).show();
                 */
                //invalidate();
                break;
            case MotionEvent.ACTION_POINTER_ID_MASK :
                /*X = (int) ev.getX();
                Y = (int) ev.getY();



                invalidate();*/
                break;
            }

            return true;
        }

        @Override
        public void onDraw(Canvas canvas) {
            super.onDraw(canvas);
            DisplayMetrics displaymetrics = new DisplayMetrics();
            getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
            int ht = displaymetrics.heightPixels;
            int wt = displaymetrics.widthPixels;
            int heightbitmap = bgr.getHeight();
            int widthbitmap = bgr.getWidth();
            int minus = wt - widthbitmap;

            // draw background
            canvas.drawBitmap(bgr, minus / 2, 0, null);
            // copy the default overlay into temporary overlay and punch a hole
            // in it
            c2.drawBitmap(overlayDefault, 360, 0, null); // exclude this line to
                                                            // show all as you
            Bitmap _scratch = BitmapFactory.decodeResource(getResources(), R.drawable.diff_6);                                              // draw

            //c2.drawBitmap(_scratch, 10, 10, pTouch);
            if(X >= 470 & X <= 522)
            {
                if(Y >= 255 & Y<= 330)
                {   
                //c2.drawRect(X, Y, 5, 5, pTouch);
                    double outer_radius = 0.5 * Math.sqrt((_scratch.getWidth()) * (_scratch.getWidth())+ (_scratch.getHeight()) * (_scratch.getHeight()));  
                 float f = (float) outer_radius;


                    c2.drawCircle(X, Y, f, pTouch);
                }

            }   


            // draw the overlay over the background
            canvas.drawBitmap(overlay, minus/2, 0, null);

        }

    }

}

Problem::
when i touch on screen circle are stay at right side of my finger Like this.
but i need it center of my finger please help on this

Answer 1

The problem is because you create ‘overlay’ with respect to the x and y cordinates from the touch event and later copying this onto the background with an offset (minus/2). Assuming your background image is smaller than the screen resolution the circle will always shift right and hence will look the circle is at the right of your finger.

If you use a background image which has same resolution as the screen dimensions , you will get properly drawn circle, with its centre at the point of touch.