绘制圆形ImageView

/**
     * Returns a circular cropped version of the bitmap passed in.
     */
    public static Bitmap getCroppedBitmap(Bitmap bitmap) {
        Bitmap output = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(),
                Config.ARGB_8888);

        final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());

        Canvas canvas = new Canvas(output);

        final Paint paint = new Paint();
        paint.setAntiAlias(true);

        int halfWidth = bitmap.getWidth() / 2;
        int halfHeight = bitmap.getHeight() / 2;

        canvas.drawCircle(halfWidth, halfHeight, Math.max(halfWidth, halfHeight), paint);

        paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));

        canvas.drawBitmap(bitmap, rect, rect, paint);

        return output;
    }