仿微信朋友圈-发红包看图片效果

代码很简单，采用BitmapShader的复制图片机制实现。用法与ImageView相同，可设置模糊度setBlurDegree以及显示半径setRadius

public class TouchImageView extends ImageView {
private float radius = 70;
private float blurDegree=200;
private Paint paint = null;
private Bitmap blurBitmap=null;

private float x;
private float y;
private boolean shouldDrawOpening = false;

public TouchImageView(Context context) {
    super(context);
}

public TouchImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public void setRadius(float radius) {
    this.radius = radius;
}
public void setBlurDegree(float blurDegree){
    this.blurDegree = blurDegree;
}

@Override
public boolean onTouchEvent(MotionEvent motionEvent) {
    int action = motionEvent.getAction();
    shouldDrawOpening = (action == MotionEvent.ACTION_DOWN || action == MotionEvent.ACTION_MOVE);
    x = motionEvent.getX();
    y = motionEvent.getY();
    invalidate();
    return true;
}

@Override
protected void onDraw(Canvas canvas) {
    if (paint == null || blurBitmap == null) {
        //创建与ImageView相同大小的画布
        Bitmap original = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
        Canvas originalCanvas = new Canvas(original);

        //第一次，新建canvas，并绘制。但是注意：再第二次调用onDraw方法时，不会绘制并且不会保存。
        super.onDraw(originalCanvas);

        //根据原始图片创建Shader，画笔将按照原始图片画图。
        Shader shader = new BitmapShader(original, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        paint = new Paint();
        paint.setShader(shader);

        //创建模糊图片
        blurBitmap = blur(original, blurDegree);
    }
    //将模糊图片绘制在ImageView原始画布上
    canvas.drawBitmap(blurBitmap, 0, 0, paint);
    if (shouldDrawOpening) {
        //根据原始图片以及Shader，画笔按照原始图片画圆
        canvas.drawCircle(x, y - radius, radius, paint);
    }
}

private Bitmap blur(Bitmap original, float radius) {
    Bitmap bitmap = Bitmap.createBitmap(original);
    return Blur.fastBlur(bitmap, (int) radius, true);
}
}