开抗锯齿后的点的问题

dahuatttt

书上这么说的：
When antialiasing is enabled,the range of supported point sizes is not necessarily continuous.The only size for the openGL specification requires support with antialiasing is 1.0. If an unsupported size is used,it will be rounded to the nearest supported value.To find out the range of sizes your implementation supports,you can call glGet() with GL_POINT_SIZE_RANGE,and you can use GL_POINT_SIZE_GRANULARITY to find the size difference between adjacent supported sizes.

这里为什么说点的大小范围不是连续的？
抗锯齿时唯一的大小是1.0?那之后怎么为什么还能调节大小？这是难道指填充锯齿的大小？
我不就是画个点吗？为什么又是GL_POINT_SIZE_RANGE的又是GL_POINT_SIZE_GRANULARITY的？？

本人愚笨，不用各位再提醒我这一点。

请直接帮忙回答问题就行，谢谢