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);
    }
}