I'm not sure this is the right subforum for my problem/question. If it isn't, please move it to wherever it belongs.

It's possible to enable a trail for NAILS:



However, I noticed that the nail trail doesn't appear in old demos. I'd be surprised if it was a KTX feature and not just some particle effect, but then why would it work in one demo and not the other? The nail trail is relatively essential to my project, so I'd really appreciate if someone could help me out.

nails can be sent one of three ways.
regular entity: nails are sent in context with an index in the same way that everything is. delta compressed etc. trails work fine as the current and previous positions are known always. same idea as rocket trails
mvd-style, nails are packed as origin/angles with a nail index allowing you to track where it was in the last packet so it can be interpolated. nails can be enabled with extra code.
qw-style nails are packed as origin/angles. the next packet that is received removes all. there is no previous state known about the nail. the best you can do is figure out directions and positions in the previous packet. not 100% reliable. this would take more code that any coder really deams it to be worth, when you can just toggle a cvar on the server.

sv_nailhack 1 will send all nails as regular entities, rather than treating them differently (the name derives from a hexedit hack of the server promoted by qizmo).
0 uses the special handling, which means the client can't track the nail from one frame to the next. they just disappear and brand new ones appear at some other location, as far as the client can tell. hence no trails.