Android 获取一个半透明的背景

/**
     * 获取一块半透明背景
     * @param rect 背景大小
     * @param color 背景颜色
     * @param aplha 背景透明度
     */
    public static Bitmap getGlass(Size rect, int color, int aplha){
        Bitmap nb = Bitmap.createBitmap(rect.width, rect.height, Config.ARGB_8888) ;
        Canvas canvas = new Canvas(nb) ;
        Paint paint = new Paint() ;
        paint.setStyle(Style.FILL);
        paint.setColor(color);
        paint.setAlpha(aplha);
        canvas.drawRect(0, 0, rect.width, rect.height, paint);
        return nb ; 
    }