This is a demonstration of the new vector-related scripting commands available in OS 3.1. Read about it here: http://www.halomods.com/ips/index.php?/topic/6-open-sauce-halo-custom-edition/page__view__findpost__p__7383 . Other exciting features include an automatic in-game map downloader and support for 4 grenade types!
(Everything else in this video is incidental to the OS feature demo, don't get too worked up about it)
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Halo Custom Edition, sometimes abbreviated Halo CE (which is also often accepted as an...