Topic on Talk:Painkiller
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Randomguy7's Fix Compilation ("Mega Patch" on PCGW) already adds proper widescreen support, Widescreen HUD Fix could be removed from the article (https://pcgamingwiki.com/wiki/Painkiller#Video_settings).
I don't know if the implementation differs, personally I play in 4:3 as every fix appears to stretch at least FMVs and menus.