Google Android - это несложно

Код: Выделить всё

mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));

Код: Выделить всё

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
	android:id="@+id/rl"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content" >
    
    
</RelativeLayout>

Код: Выделить всё

package ru.test.CanvasTest2;

import ru.test.CanvasTest2.R.drawable;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;
import android.widget.RelativeLayout;

public class MainActivity extends Activity {
	
	private Paint mPaint;
	
	
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        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(12);
        
        RelativeLayout rl = (RelativeLayout) findViewById(R.id.rl);
        
        ImageView iv = new ImageView(this);
        iv.setImageResource(drawable.ic_launcher);
        rl.addView(iv);
        
        MyImageView miv = new MyImageView(this);
        miv.setImageBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher_red));
        
        rl.addView(miv);
    }
    
    public class MyImageView extends ImageView {

    	private Paint paint;
    	private Canvas c2;
    	private Bitmap overlay;
    	private Path path;
    	
		public MyImageView(Context context) {
			super(context);
			
			paint = new Paint();
			path = new Path();
			
			paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR)); 
            paint.setColor(Color.TRANSPARENT); 
            paint.setStyle(Paint.Style.STROKE); 
            paint.setStrokeJoin(Paint.Join.ROUND); 
            paint.setStrokeWidth(12); 
            paint.setAntiAlias(true);
		}
    	
		@Override
		public void setImageBitmap(Bitmap bm) {
			 super.setImageBitmap(bm);
			 Drawable bd = getDrawable(); 
             if(bd == null) {
            	 return; 
             } 

             Bitmap fullSizeBitmap = ((BitmapDrawable) bd).getBitmap(); 
             overlay = fullSizeBitmap.copy(Config.ARGB_8888, true);
             c2 = new Canvas(overlay);
		}
		
		@Override
		protected void onDraw(Canvas canvas) {
			//super.onDraw(canvas);
			
			Drawable bd = getDrawable(); 
            if(bd == null) {
            	return; 
            } 
            
            Bitmap fullSizeBitmap = ((BitmapDrawable) bd).getBitmap(); 
            if(fullSizeBitmap != null && c2 != null) {
            	canvas.drawColor(Color.TRANSPARENT); 
                c2.drawBitmap(fullSizeBitmap, 0, 0, null); 
                c2.drawPath(path, paint); 
                canvas.drawBitmap(overlay, 0, 0, null); 
            }
	}
    }
}

Код: Выделить всё

package ru.KamiSempai.LotteryLayer;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class LotteryLayer extends View {
	private final static int COATING_COLOR = Color.DKGRAY;
	private final static int PAINT_WIDTH = 24;

	private Paint mPaint;
	private Bitmap mBitmap;
	private Canvas mCanvas;
	private Paint mBitmapPaint;

	public LotteryLayer(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
		initialise();
	}

	public LotteryLayer(Context context, AttributeSet attrs) {
		super(context, attrs);
		initialise();
	}

	public LotteryLayer(Context context) {
		super(context);
		initialise();
	}

	private void initialise() {
		mBitmapPaint = new Paint(Paint.DITHER_FLAG);
		mPaint = new Paint();
		mPaint.setStyle(Paint.Style.STROKE);
		mPaint.setStrokeJoin(Paint.Join.ROUND);
		mPaint.setStrokeCap(Paint.Cap.ROUND);
		mPaint.setStrokeWidth(PAINT_WIDTH);
		mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
	}

	private Bitmap getBitmap() {
		if (mBitmap == null) {
			mBitmap = Bitmap.createBitmap(getMeasuredWidth(),
					getMeasuredHeight(), Bitmap.Config.ARGB_8888);
			mCanvas = new Canvas(mBitmap);
			mCanvas.drawColor(COATING_COLOR);
		}
		return mBitmap;
	}

	@Override
	protected void onDraw(Canvas canvas) {
		canvas.drawBitmap(getBitmap(), 0, 0, mBitmapPaint);
	}

	private float mX, mY;

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		float x = event.getX();
		float y = event.getY();

		if (event.getAction() == MotionEvent.ACTION_MOVE) {
			mCanvas.drawLine(mX, mY, x, y, mPaint);
			invalidate();
		}
		mX = x;
		mY = y;
		return true;
	}
}

Код: Выделить всё

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/ic_launcher" >
    <ru.KamiSempai.LotteryLayer.LotteryLayer
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</FrameLayout>