近似值。 实际字符点的高和宽非常取决于字体风格和特别的字符。所以有些字符会比实际要求点的尺寸小或大。 所有矢量字体基准线是点的单元尺寸当场计算的。基准线是单元顶到底的四分之三(Approximation.The actual height and width of the character points depends very much on the font style and the particular character.So some characters are going to