Is there a tool for previewing both LaTeX and MetaPost files?

I'm trying to find a tool for Windows that I can use to preview .tex and .mp files as they are saved. Does such a tool exist? I have TeXworks installed which has a handy build button (this displays the result in another window), but I'd rather use Emacs. Also, TeXworks does not compile .mp files.

Perhaps there's a more elegant way to preview files, other than the a开发者_如何学Gopproach I'm thinking of.

Solution is to use pdflatex and Sumatra PDF, since this viewer auto-reloads the file.