本Demo旨在实现刮刮卡效果，优点是可自由实现刮层下的内容，附赠一个可随路径移动的橡皮擦。
在写正文之前，先感谢一下鸿洋大神的【Android 自定义控件实现刮刮卡效果 真的就只是刮刮卡么】这篇文章，此文章手把手教你实现一个刮刮卡效果，有助于从0开始理解刮奖效果是怎么实现的（绝大多数的刮奖效果实现原理是一样的）。
效果图
trimmedVideo_eo_20190726_175154.gif
实现
刮奖效果实现的核心是PorterDuffXfermode这个类，PorterDuffXfermode是一种集合概念，交集、并集等图像的混合显示模式。它提供了16个常用Mode，而我这里将要使用的Mode是PorterDuff.Mode.CLEAR，clear的意思很直白，清除。此外还有一个Mode， PorterDuff.Mode.DST_OUT可以使用，此处这两个Mode实现的效果是一样的。PorterDuffXfermode所有Mode的使用效果请自行百度。
刮奖效果实现原理
将Bitmap设置成底层画板，创建画笔，设置画笔Xfermode为PorterDuff.Mode.CLEAR，然后重写onTouchEvent，使用画笔画出手势移动的路径，那么画笔所经过的地方就会被擦除。
GuaGuaKaLayer.java
import android.content.Context;
import android.content.res.Resources;
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.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import com.adminstrator.guaguakaapplication.R;
/**
* Created by Administrator on 2019/7/26.
* 刮刮卡的蒙层View
*/
public class GuaGuaKaLayer extends View {
/**
* 绘制线条的Paint,即用户手指绘制Path
*/
private Paint mOutterPaint = new Paint();
/**
* 记录用户绘制的Path
*/
private Path mPath = new Path();
/**
* 内存中创建的Canvas
*/
private Canvas mCanvas;
/**
* mCanvas绘制内容在其上
*/
private Bitmap mBitmap;
/**
* 蒙层和橡皮擦
* */
private Bitmap mBackBitmap;
private Bitmap moveBitmap;
/**
* 记录手势移动位置
* */
private int mLastX;
private int mLastY;
/**
* 用于判断何时算刮开完成
* */
private boolean isComplete = false;
/**
* 用于判断是否显示橡皮擦
* */
private boolean isDownOrMove = false;
private Resources resources;
public GuaGuaKaLayer(Context context) {
this(context, null);
}
public GuaGuaKaLayer(Context context, @Nullable AttributeSet attrs) {
this(context, attrs, 0);
}
public GuaGuaKaLayer(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
resources = context.getResources();
init();
}
private void init() {
mPath = new Path();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int width = getMeasuredWidth();
int height = getMeasuredHeight();
//初始化bitmap
mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
//设置画笔
mOutterPaint.setColor(Color.RED);
mOutterPaint.setAntiAlias(true);
mOutterPaint.setDither(true);
mOutterPaint.setStyle(Paint.Style.STROKE);
mOutterPaint.setStrokeJoin(Paint.Join.ROUND);
mOutterPaint.setStrokeCap(Paint.Cap.ROUND);
//设置画笔宽度
mOutterPaint.setStrokeWidth(20);
//将Bitmap精确缩放到指定的大小
Bitmap tempBackBitmap = Bitmap.createBitmap(BitmapFactory.decodeResource(resources, R.drawable.guaguaceng));
Bitmap tempMoveBitmap = Bitmap.createBitmap(BitmapFactory.decodeResource(resources, R.drawable.cleaner));
moveBitmap = Bitmap.createScaledBitmap(tempMoveBitmap,100,100,true);
mBackBitmap= Bitmap.createScaledBitmap(tempBackBitmap, width, height, true);
mCanvas.drawBitmap(mBackBitmap, 0, 0, null);
}
@Override
protected void onDraw(Canvas canvas) {
if (!isComplete) {
drawPath();
canvas.drawBitmap(mBitmap, 0, 0, null);
if(isDownOrMove){
//绘制橡皮擦
canvas.drawBitmap(moveBitmap, mLastX - moveBitmap.getWidth()/2, mLastY - moveBitmap.getHeight()/2, null);
}
}
}
/**
* 绘制线条
* */
private void drawPath() {
mOutterPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
// mOutterPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
mCanvas.drawPath(mPath, mOutterPaint);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
int x = (int) event.getX();
int y = (int) event.getY();
switch (action) {
case MotionEvent.ACTION_DOWN:
mLastX = x;
mLastY = y;
mPath.moveTo(mLastX, mLastY);
isDownOrMove = true;
break;
case MotionEvent.ACTION_MOVE:
int dx = Math.abs(x - mLastX);
int dy = Math.abs(y - mLastY);
if (dx > 3 || dy > 3) {
mPath.lineTo(x, y);
}
mLastX = x;
mLastY = y;
isDownOrMove = true;
break;
case MotionEvent.ACTION_UP:
isDownOrMove = false;
new Thread(mRunnable).start();
break;
}
invalidate();
return true;
}
/**
* 统计擦除区域任务
*/
private Runnable mRunnable = new Runnable() {
private int[] mPixels;
@Override
public void run() {
int w = getWidth();
int h = getHeight();
float wipeArea = 0;
float totalArea = w * h;
Bitmap bitmap = mBitmap;
mPixels = new int[w * h];
/**
* 拿到所有的像素信息
*/
bitmap.getPixels(mPixels, 0, w, 0, 0, w, h);
/**
* 遍历统计擦除的区域
*/
for (int i = 0; i < w; i++) {
for (int j = 0; j < h; j++) {
int index = i + j * w;
//被擦除
if (mPixels[index] == 0) {
wipeArea++;
}
}
}
/**
* 根据所占百分比，进行一些操作
*/
if (wipeArea > 0 && totalArea > 0) {
int percent = (int) (wipeArea * 100 / totalArea);
if (percent > 70) {
isComplete = true;
postInvalidate();
}
}
}
};
}
使用
在布局文件中使用FrameLayout包裹刮刮乐底层内容和蒙层
文件中TextView可替换成任意控件和布局，自由实现刮层下的内容