XY billboarding and static objects

[Matt]

1. Turn on XY billboarding for all sprites.
2. Walk right up to a torch.
3. Look down.

Expected: the torch is still perpendicular to your view (but definitely not perpendicular to the ground), but animates as normal.

Actual: the above, but it throbs.

I'm not reporting this as a bug because I can only assume it's something that can't be fixed, but what even causes this?

(Relatedly, a similar throb/twitch happens even in vanilla if you have a looping animation where the image dimensions of the frames are not the same throughout. Is this an unavoidable engine thing or a Doom rendering quirk/bug?)

[Professor Hastig]

XY billboarding appears to rotate around the sprite's center. If the sprites have a bottom-center offset this will mean that the pivot point changes depending on the actual sprite size.

If you ask me, the entire feature is only useful for projectile sprites where the sprite origin is in the center, but the current settings won't allow this restriction.

[Nash]

I think the user's "sprite clipping" setting further permutates the behavior. It's very unpredictable.

[Matt]

Thanks for the explanation!

I generally set everything to XY just because monsters and pickups and projectiles - i.e., all the stuff i typically actually interact with - look so bad up close (or disappear entirely when they're right above or under you) [EDIT: in Y billboarding] and compared to that this is a very minor visual annoyance that can be solved with mods anyway.

I've messed with the sprite clipping setting and it makes surprisingly little difference for better or for worse.

[KynikossDragonn]

I turn the "Adjust sprite clipping" completely off for this very reason. Yes, it does make certain stuff sink into the ground, but unless someone has a crazy hairbrained idea to make GZDoom render sprites through certain floor depths like the vanilla rendering engine does, I'd rather just keep this thing off entirely to avoid the "bobbing" problem.

[Graf Zahl]

I generally set everything to XY just because monsters and pickups and projectiles - i.e., all the stuff i typically actually interact with - look so bad up close (or disappear entirely when they're right above or under you) and compared to that this is a very minor visual annoyance that can be solved with mods anyway.

I never use XY billboarding because in the context of Doom it flat out sucks and creates far too many problems. It is one of those features I'd remove in an instant if I could because it is impossible to make it work right. The entire sprite renderer is an epic disaster because far too many people have injected their ideology without ever thinking about the bigger picture.

As a result it's all in a state where really useful things like properly working wall and floor sprites are simply not possible.