Android自定义橡皮擦效果

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public class picFingerToTest extends View {

  private Paint paint;
  private Bitmap decodeResourceSRC;
  private Bitmap createBitmapDST;
  // 手指路径，使用贝塞尔路线
  private Path path;
  private float perX;
  private float perY;

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

    // 2、设置手指画笔
    paint = new Paint();
    paint.setAntiAlias(true);
    paint.setColor(Color.RED);
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeWidth(45);

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

  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    // 分层绘制
    int saveLayer = canvas.saveLayer(0, 0, getWidth(), getHeight(), null,Canvas.ALL_SAVE_FLAG);

    // 把手指轨迹划到目标路径上
    Canvas canvas2 = new Canvas(createBitmapDST);
    canvas2.drawPath(path, paint);

    // 把目标图像画到画布上
    canvas.drawBitmap(createBitmapDST, 0, 0, paint);

    // 计算源图像区域

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

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

  }

  //使用贝塞尔曲线，使折线过度圆滑
  @Override
  public boolean onTouchEvent(MotionEvent event) {

    switch (event.getAction()) {
    // 记录手指触摸的初始化位置
    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);
  }

}

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public void onCreate() {
  //底边图片
  ImageView ivTop = (ImageView) findViewByid(R.id.iv_top);
 
  Options opts = new Options(); //图片加载器，用于配置一些缩放比例，和像素单位
  opts.inSampleSize = 2; //制定加载器把原图片的宽高缩放到2/1的效果加载
  //获得外层图片,decodeResource方法默认获得的像素单位是RGB(red,green,blue),ARGB(alpha,red,green,blue)
  Bitmap topImage = BitmapFactory.decodeResources( getResource(),R.drawable.top, opts);
 
  //创建一张空白图片，并且把图片想读单位指定为:ARGB
  Bitmap blank = Bitmap.createBitmap(topImage.getWidth(), topImage.getHeight, Config.ARGB_4444);
 
  //把上边的topImage画到空白图片上
  Canvas canvas = new Canvas(blank);
  //把topImage画到空白图片上但是像素单位变成ARGB()
  canvas.drawBitmap(topImage, 0, 0, null);
  ivTop.setImageBitmap(blank);
}
 
class MyOnTouchListoner implements OnTouchListener {
 
  @Override pulic boolean OnTouch(View v, MotionEvent event) {
    //是否是移动的事件
    if (event.getAction() == MotionEvent.ACTION_MOVE) {
      //获得按下坐标
      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++) {
          //防止超出边界
          if (j >= 0 && blank.getHeight() && i >= 0 && i < blank.getWidth()) {
            blank.setPixel(i, j, Color.TRANSPARENT);
          }
        }
      }
      //修改后的图片设置给ImageView
      ivTop.setImageBitmap(blank);
    }
 
    return true; //true 消耗掉这次触摸事件.false 不消耗
  }
 
}