/**
     * 转换图片成圆形
     * @param bitmap 传入Bitmap对象
     * @return
     */
    public static Bitmap toRoundBitmap(Bitmap bitmap) {
        int width = bitmap.getWidth();
        int height = bitmap.getHeight();
        float roundPx;
        float left,top,right,bottom,dst_left,dst_top,dst_right,dst_bottom;
        if (width <= height) {
                roundPx = width / 2;
                top = 0;
                bottom = width;
                left = 0;
                right = width;
                height = width;
                dst_left = 0;
                dst_top = 0;
                dst_right = width;
                dst_bottom = width;
        } else {
                roundPx = height / 2;
                float clip = (width - height) / 2;
                left = clip;
                right = width - clip;
                top = 0;
                bottom = height;
                width = height;
                dst_left = 0;
                dst_top = 0;
                dst_right = height;
                dst_bottom = height;
        }
             
        Bitmap output = Bitmap.createBitmap(width,
                        height, Config.ARGB_8888);
        Canvas canvas = new Canvas(output);
             
        final int color = 0xff424242;
        final Paint paint = new Paint();
        final Rect src = new Rect((int)left, (int)top, (int)right, (int)bottom);
        final Rect dst = new Rect((int)dst_left, (int)dst_top, (int)dst_right, (int)dst_bottom);
        final RectF rectF = new RectF(dst);
        paint.setAntiAlias(true);
             
        canvas.drawARGB(0, 0, 0, 0);
        paint.setColor(color);
        canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
        paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
        canvas.drawBitmap(bitmap, src, dst, paint);
        return output;
    }