threerings/flump — comment on commit 0b712bc1fe024ffdbae6342d55f57670ad9c8b6f
File:  line 0
By groves:

I don't think scale-9 is possible in the GPU without some special processing. You'd have to split the texture up into the 9 slices and then scale those properly in the runtime, which seems like a pain. I'd avoid it unless absolutely necessary.