Android 自定义橡皮擦效果

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);
}

}