Android自定義橡皮擦效果

public class picFingerToTest extends View {

  private Paint paint;
  private Bitmap decodeResourceSRC;
  private Bitmap createBitmapDST;
  // 手指路徑，使用貝塞爾路線
  private Path path;
  private float perX;
  private float perY;

  public picFingerToTest(Context context, AttributeSet attrs) {
    super(context, attrs);
    // 1、設(shè)置禁用硬件設(shè)置
    setLayerType(View.LAYER_TYPE_SOFTWARE, null);

    // 2、設(shè)置手指畫筆
    paint = new Paint();
    paint.setAntiAlias(true);
    paint.setColor(Color.RED);
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeWidth(45);

    // 3、生成圖像手指源目標
    // 源
    decodeResourceSRC = BitmapFactory.decodeResource(getResources(), R.drawable.welcome, null);
    // 目標
    createBitmapDST = Bitmap.createBitmap(decodeResourceSRC.getWidth(), decodeResourceSRC.getHeight(),
        Config.ARGB_8888);
    path = new Path();

  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    // 分層繪制
    int saveLayer = canvas.saveLayer(0, 0, getWidth(), getHeight(), null,Canvas.ALL_SAVE_FLAG);

    // 把手指軌跡劃到目標路徑上
    Canvas canvas2 = new Canvas(createBitmapDST);
    canvas2.drawPath(path, paint);

    // 把目標圖像畫到畫布上
    canvas.drawBitmap(createBitmapDST, 0, 0, paint);

    // 計算源圖像區(qū)域

    paint.setXfermode(new PorterDuffXfermode(Mode.SRC_OUT));
    canvas.drawBitmap(decodeResourceSRC, 0, 0, paint);

    paint.setXfermode(null);
    canvas.restoreToCount(saveLayer);

  }

  //使用貝塞爾曲線，使折線過度圓滑
  @Override
  public boolean onTouchEvent(MotionEvent event) {

    switch (event.getAction()) {
    // 記錄手指觸摸的初始化位置
    case MotionEvent.ACTION_DOWN:

      path.moveTo(event.getX(), event.getY());

      perX = event.getX();
      perY = event.getY();

      return true;

    case MotionEvent.ACTION_MOVE:

      float endX = (perX + event.getX()) / 2;
      float endY = (perY + event.getY()) / 2;

      path.quadTo(perX, perY, endX, endY);
      perX = event.getX();
      perY = event.getY();
      postInvalidate();

      break;
    case MotionEvent.ACTION_UP:

      break;

    default:
      break;
    }

    return super.onTouchEvent(event);
  }

}

public void onCreate() {
  //底邊圖片
  ImageView ivTop = (ImageView) findViewByid(R.id.iv_top);
 
  Options opts = new Options(); //圖片加載器，用于配置一些縮放比例，和像素單位
  opts.inSampleSize = 2; //制定加載器把原圖片的寬高縮放到2/1的效果加載
  //獲得外層圖片,decodeResource方法默認獲得的像素單位是RGB(red,green,blue),ARGB(alpha,red,green,blue)
  Bitmap topImage = BitmapFactory.decodeResources( getResource(),R.drawable.top, opts);
 
  //創(chuàng)建一張空白圖片，并且把圖片想讀單位指定為:ARGB
  Bitmap blank = Bitmap.createBitmap(topImage.getWidth(), topImage.getHeight, Config.ARGB_4444);
 
  //把上邊的topImage畫到空白圖片上
  Canvas canvas = new Canvas(blank);
  //把topImage畫到空白圖片上但是像素單位變成ARGB()
  canvas.drawBitmap(topImage, 0, 0, null);
  ivTop.setImageBitmap(blank);
}
 
class MyOnTouchListoner implements OnTouchListener {
 
  @Override pulic boolean OnTouch(View v, MotionEvent event) {
    //是否是移動的事件
    if (event.getAction() == MotionEvent.ACTION_MOVE) {
      //獲得按下坐標
      int x = (int) event.getX();
      int y = (int) event.getY();
 
      for (int i = x - 10; i < x + 10; i++) {
        for (int j = y - 10; j < y + 10; j++) {
          //防止超出邊界
          if (j >= 0 && blank.getHeight() && i >= 0 && i < blank.getWidth()) {
            blank.setPixel(i, j, Color.TRANSPARENT);
          }
        }
      }
      //修改后的圖片設(shè)置給ImageView
      ivTop.setImageBitmap(blank);
    }
 
    return true; //true 消耗掉這次觸摸事件.false 不消耗
  }
 
}