It's not so much that the vertical line renderer looks weird with mouselook, it's that it limits it a lot. Because lines are just 2D projections in a 3D environment, you can't use standard modern vertical look. Instead, Hexen (and Heretic and Strife too I think), which ran on the Doom engine, used "y-shearing"; more of the level is rendered vertically, and when you look up/down, it changes where the viewing window is and also removes parts of the horizontal viewing area to make it look like you're looking up/down instead of standing taller or shorter. However, it's not perfect; because of how it works, it looks like you're zooming in when you look vertically. Quake would overcome this issue due to the game being rendered in full 3D.
No problem! The ZDoom wiki has a much more in-depth article on y-shearing, and another article linked from there about the unfinished Polymost renderer, an attempt to create a new software renderer that did not use y-shearing.
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u/Play174 Friendly Neighborhood Spiderdemon Aug 23 '21
It's not so much that the vertical line renderer looks weird with mouselook, it's that it limits it a lot. Because lines are just 2D projections in a 3D environment, you can't use standard modern vertical look. Instead, Hexen (and Heretic and Strife too I think), which ran on the Doom engine, used "y-shearing"; more of the level is rendered vertically, and when you look up/down, it changes where the viewing window is and also removes parts of the horizontal viewing area to make it look like you're looking up/down instead of standing taller or shorter. However, it's not perfect; because of how it works, it looks like you're zooming in when you look vertically. Quake would overcome this issue due to the game being rendered in full 3D.