By default, hats that do not cover full head will not cover the hair. For hats that cover full head but do not have textures that cover the head, I have already applied patches. After the 1.5 texture rendering major changes, this has become easy to do without the need to make wheels yourself,
Just add it to <apparel> :
<renderSkipFlags>
<li>None</li>
</renderSkipFlags>
And it will work, really easy.
In addition, the narrow head shape of Facial Animation reduces the width of the head, which looks good, but the hat does not have the same scaling, so if you use Facial Animation, this will keep the ratio of the hat to the head consistent. And to be honest, the wide head shape under Facial Animation is really ugly. I have a small patch to replace them, but it's too small and doesn't feel worth uploading.
You might say, hey, aren't there already many mods that don't hide hair from hats? Yes, but they are too manually controlled. For example, the one I commonly use defaults to not displaying after each hat is added, and you can only display all or not display all with one click, or manually adjust them one by one. I don't think it's necessary to be so complicated, in fact it's quite simple.
