The early Doom 1 and 2 being software renderers, used ray casting (386 protected mode FTW to boot!) The later versions though, were part of the first wave of g

The early Doom 1 and 2 being software renderers, used ray casting (386 protected mode FTW to boot!) The later versions though, were part of the first wave of games to leverage GPU cards. I don't know if those newer releases still kept any ability to render purely in software though.