package com.clock.scratch;

import ...;

/**
 * Created by Clock on 2016/8/26.
 */
public class ScratchView extends View {

 ...

 public ScratchView(Context context) {
  super(context);
  TypedArray typedArray = context.obtainStyledAttributes(R.styleable.ScratchView);
  init(typedArray);
 }

 ...

 private void init(TypedArray typedArray) {
  ...
  mMaskColor = typedArray.getColor(R.styleable.ScratchView_maskColor, DEFAULT_MASKER_COLOR);

  mMaskPaint = new Paint();
  mMaskPaint.setAntiAlias(true);//抗锯齿
  mMaskPaint.setDither(true);//防抖
  setMaskColor(mMaskColor);
  ...

 }

 /**
  * 设置蒙板颜色
  *
  * @param color 十六进制颜色值，如：0xffff0000（不透明的红色）
  */
 public void setMaskColor(int color) {
  mMaskPaint.setColor(color);
 }

 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  canvas.drawBitmap(mMaskBitmap, 0, 0, mBitmapPaint);//绘制图层遮罩
 }

 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
  super.onSizeChanged(w, h, oldw, oldh);
  createMasker(w, h);
 }

 /**
  * 创建蒙层
  *
  * @param width
  * @param height
  */
 private void createMasker(int width, int height) {
  mMaskBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
  mMaskCanvas = new Canvas(mMaskBitmap);
  Rect rect = new Rect(0, 0, width, height);
  mMaskCanvas.drawRect(rect, mMaskPaint);//绘制生成和控件大小一致的遮罩 Bitmap
 }

}

<?xml version="1.0" encoding="utf-8"?>
<resources>
 <declare-styleable name="ScratchView">
  <!--蒙层的颜色-->
  <attr name="maskColor" format="color|reference" />
 </declare-styleable>

</resources>

<FrameLayout
  android:layout_width="200dp"
  android:layout_height="200dp"
  android:layout_gravity="center_horizontal"
  android:layout_marginTop="8dp">
  <!--刮层下遮住的内容-->
  <ImageView
   android:layout_width="150dp"
   android:layout_height="150dp"
   android:layout_gravity="center"
   android:src="@mipmap/lufy" />
  <!--刮层-->
  <com.clock.scratch.ScratchView
   android:id="@+id/scratch_view"
   android:layout_width="match_parent"
   android:layout_height="match_parent" />
 </FrameLayout>

package com.clock.scratch;

import ...;

public class ScratchView extends View {

 public ScratchView(Context context) {
  super(context);
  TypedArray typedArray = context.obtainStyledAttributes(R.styleable.ScratchView);
  init(typedArray);
 }

 private void init(TypedArray typedArray) {
  mEraseSize = typedArray.getFloat(R.styleable.ScratchView_eraseSize, DEFAULT_ERASER_SIZE);
  ...

  mErasePaint = new Paint();
  mErasePaint.setAntiAlias(true);
  mErasePaint.setDither(true);
  mErasePaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));//设置擦除效果
  mErasePaint.setStyle(Paint.Style.STROKE);
  mErasePaint.setStrokeCap(Paint.Cap.ROUND);//设置笔尖形状，让绘制的边缘圆滑
  setEraserSize(mEraseSize);

  mErasePath = new Path();

  ViewConfiguration viewConfiguration = ViewConfiguration.get(getContext());
  mTouchSlop = viewConfiguration.getScaledTouchSlop();

 }

 /**
  * 设置橡皮檫尺寸大小（默认大小是 60）
  *
  * @param eraserSize 橡皮檫尺寸大小
  */
 public void setEraserSize(float eraserSize) {
  mErasePaint.setStrokeWidth(eraserSize);
 }

 @Override
 public boolean onTouchEvent(MotionEvent event) {
  int action = event.getAction();
  switch (action) {
   case MotionEvent.ACTION_DOWN:
    startErase(event.getX(), event.getY());
    invalidate();
    return true;
   case MotionEvent.ACTION_MOVE:
    erase(event.getX(), event.getY());
    invalidate();
    return true;
   case MotionEvent.ACTION_UP:
    stopErase();
    invalidate();
    return true;
   default:
    break;
  }
  return super.onTouchEvent(event);
 }

 /**
  * 开始擦除
  *
  * @param x
  * @param y
  */
 private void startErase(float x, float y) {
  mErasePath.reset();
  mErasePath.moveTo(x, y);
  this.mStartX = x;
  this.mStartY = y;
 }

 /**
  * 擦除
  *
  * @param x
  * @param y
  */
 private void erase(float x, float y) {
  int dx = (int) Math.abs(x - mStartX);
  int dy = (int) Math.abs(y - mStartY);
  if (dx >= mTouchSlop || dy >= mTouchSlop) {
   this.mStartX = x;
   this.mStartY = y;

   mErasePath.lineTo(x, y);
   mMaskCanvas.drawPath(mErasePath, mErasePaint);

   mErasePath.reset();
   mErasePath.moveTo(mStartX, mStartY);
  }
 }


 /**
  * 停止擦除
  */
 private void stopErase() {
  this.mStartX = 0;
  this.mStartY = 0;
  mErasePath.reset();
 }

}

<?xml version="1.0" encoding="utf-8"?>
<resources>
 <declare-styleable name="ScratchView">
  <!--擦除尺寸大小-->
  <attr name="eraseSize" format="float" />
 </declare-styleable>

</resources>

 /**
  * 设置水印图标
  *
  * @param resId 图标资源id，-1表示去除水印
  */
 public void setWatermark(int resId) {
  if (resId == -1) {
   mWatermark = null;
  } else {
   Bitmap bitmap = BitmapFactory.decodeResource(getResources(), resId);
   mWatermark = new BitmapDrawable(bitmap);
   mWatermark.setTileModeXY(Shader.TileMode.REPEAT, Shader.TileMode.REPEAT);
  }
 }

 /**
  * 创建蒙层
  *
  * @param width
  * @param height
  */
 private void createMasker(int width, int height) {
  ...

  if (mWatermark != null) {//
   Rect bounds = new Rect(rect);
   mWatermark.setBounds(bounds);
   mWatermark.draw(mMaskCanvas);
  }
 }

private void onErase() {
  int width = getWidth();
  int height = getHeight();
  new AsyncTask<Integer, Integer, Boolean>() {

   @Override
   protected Boolean doInBackground(Integer... params) {
    int width = params[0];
    int height = params[1];
    int pixels[] = new int[width * height];
    mMaskBitmap.getPixels(pixels, 0, width, 0, 0, width, height);//获取覆盖图层中所有的像素信息，stride用于表示一行的像素个数有多少

    float erasePixelCount = 0;//擦除的像素个数
    float totalPixelCount = width * height;//总像素个数

    for (int pos = 0; pos < totalPixelCount; pos++) {
     if (pixels[pos] == 0) {//透明的像素值为0
      erasePixelCount++;
     }
    }

    int percent = 0;
    if (erasePixelCount >= 0 && totalPixelCount > 0) {
     percent = Math.round(erasePixelCount * 100 / totalPixelCount);
     publishProgress(percent);
    }

    return percent >= mMaxPercent;
   }

   @Override
   protected void onProgressUpdate(Integer... values) {
    super.onProgressUpdate(values);
    mPercent = values[0];
    onPercentUpdate();
   }

   @Override
   protected void onPostExecute(Boolean result) {
    super.onPostExecute(result);
    if (result && !mIsCompleted) {//标记擦除，并完成回调
     mIsCompleted = true;
     if (mEraseStatusListener != null) {
      mEraseStatusListener.onCompleted(ScratchView.this);
     }
    }
   }

  }.execute(width, height);
 }

 /**
  * 设置擦除监听器
  *
  * @param listener
  */
 public void setEraseStatusListener(EraseStatusListener listener) {
  this.mEraseStatusListener = listener;
 }

 /**
  * 擦除状态监听器
  */
 public static interface EraseStatusListener {

  /**
   * 擦除进度
   *
   * @param percent 进度值，大于0，小于等于100；
   */
  public void onProgress(int percent);

  /**
   * 擦除完成回调函数
   *
   * @param view
   */
  public void onCompleted(View view);
 }