刮刮蕾的簡單設計

package com.example.mohon.retrofitproject;

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.icu.util.Measure;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.Display;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by Mohon on 2016/10/23.
 */

public class GuaGuaLei extends View {

    private Paint paint;
    private Path path;
    private Bitmap bgBitmap;
    private Bitmap srcBitmap;
    private Canvas mCanvas;

    public GuaGuaLei(Context context) {
        super(context);
    }

    public GuaGuaLei(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public GuaGuaLei(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    private void init(Context context) {
        paint = new Paint();
        //設置透明
        paint.setAlpha(0);
        //設置層疊方式   Dst是先畫的圖形，Src是後畫的圖形
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
        paint.setStyle(Paint.Style.FILL_AND_STROKE);
        paint.setStrokeWidth(50);
        path = new Path();

        //刮刮蕾的背景圖
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inSampleSize = 2;
        bgBitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.alalei, options);

        //創建相同大小的遮蓋層
        srcBitmap = Bitmap.createBitmap(bgBitmap.getWidth(), bgBitmap.getHeight(), Bitmap.Config.ARGB_8888);

        //類似雙緩存的設計，手勢操作都是執行在srcBitmap上
        mCanvas = new Canvas(srcBitmap);
        mCanvas.drawColor(Color.GRAY);
    }


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }


    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
    }


    @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) {
        super.onDraw(canvas);
        canvas.drawBitmap(bgBitmap, 0, 0, null);
        canvas.drawBitmap(srcBitmap, 0, 0, null);
    }
}