PorterDuffXfermode實現Android刮刮卡效果

import android.annotation.SuppressLint;
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.graphics.Paint.Cap;
import android.view.MotionEvent;
import android.view.View;

public class Scrape extends View {
/**
* 刮刮卡
*/
private Bitmap mBitmap,mFgBitmap;
private Paint mPaint;
private Path mPath;
private Context mContext;
private Canvas mCanvas;
public Scrape(Context context) {
super(context);
this.mContext = context;
init();
}
private void init()
{
mPaint = new Paint();
///< 原圖
mBitmap = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.gril);
///< 底圖 也可以找兩張大小一樣的圖片代替
mFgBitmap = Bitmap.createBitmap(mBitmap.getWidth(), mBitmap.getHeight(), Bitmap.Config.ARGB_8888);
mPaint = new Paint();
///< 設置畫筆爲透明色
mPaint.setAlpha(0);
///< DST_IN模式將路徑繪製到前面覆蓋的圖層上面即可
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeWidth(50);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Cap.ROUND);
mCanvas = new Canvas(mFgBitmap);
mCanvas.drawColor(Color.GRAY);
mPath = new Path();
}
@SuppressLint(“ClickableViewAccessibility”)
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mPath.reset();
mPath.moveTo(event.getX(), event.getY());
break;
case MotionEvent.ACTION_MOVE:
mPath.lineTo(event.getX(), event.getY());
break;
default:
break;
}
mCanvas.drawPath(mPath, mPaint);
invalidate();
return true;
}
@Override
protected void onDraw(Canvas canvas) {
///< 先畫底圖
canvas.drawBitmap(mBitmap, 0, 0, null);
///< 再畫緩存的圖片
canvas.drawBitmap(mFgBitmap, 0, 0, null);
}
}