说明：  C#实现的字体阴影ShadowFont特效，实现了两种阴影字效果。一种是对文本使用去锯齿的边缘处理，在两个不同的位置绘制文本，形成阴影；另一个是以阴影为线条，构造影线画刷，先画背景再画前景，使用graphics.DrawString来绘制文字的阴影。
(The font shadow ShadowFont effect implemented by C # realizes two shadow word effects. One is to use anti-aliased edge processing on the text to draw the text at two different locations to form a shadow; the other is to use the shadow as a line to construct a shadow brush, first draw the background and then the foreground, use graphics.DrawString to Draw the shadow of the text.)