使用PorterDuffXfermode画出刮刮奖效果p146-p148

package com.zzw.Qunyinzghuan3;

import android.content.Context;
import android.graphics.Bitmap;
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.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

/**
* Created by zzw on 2016/7/12.
* 描述:
*/
public class PorterDuffXfermodeView extends View {

private Bitmap bgBmp, fgBmp;
private Paint paint;
private Canvas mCanvas;
private Path path;

public PorterDuffXfermodeView(Context context) {
this(context, null);
}

public PorterDuffXfermodeView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}

public PorterDuffXfermodeView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
paint = new Paint();
paint.setAlpha(0);//要把透明度设置为0
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.ROUND);//设置结合处的样子 Miter:结合处为锐角， Round:结合处为圆弧：BEVEL：结合处为直线。
paint.setStrokeWidth(50);
paint.setStrokeCap(Paint.Cap.ROUND);// 设置画笔转弯去的连接风格

path = new Path();
bgBmp = BitmapFactory.decodeResource(context.getResources(), R.mipmap.ic_test);
fgBmp = Bitmap.createBitmap(bgBmp.getWidth(), bgBmp.getHeight(), Bitmap.Config.ARGB_8888);

mCanvas = new Canvas(fgBmp);
mCanvas.drawColor(Color.GRAY);
}

@Override
public boolean onTouchEvent(MotionEvent event) {

switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
path.reset();
path.moveTo(event.getX(), event.getY());
break;

case MotionEvent.ACTION_MOVE:
path.lineTo(event.getX(), event.getY());
break;
}

mCanvas.drawPath(path, paint);
invalidate();

return true;
}

@Override
protected void onDraw(Canvas canvas) {
canvas.drawBitmap(bgBmp, 0, 0, null);
canvas.drawBitmap(fgBmp, 0, 0, null);
}
}