Coding impact marker without a collider?

Unity Engine
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I was trying to make a spider shoot a projectile and have that projectile instantiate a web after a certain distance traveled. I know how to do impact markers and use onCollisionEnter2d but I am brain farting on how to do this in a top-down 2d game when the projectile does not hit a collider. Can anyone point me anything that might help?

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I would imagine a Raycast in Physics2D would be useful to impacting things just ahead of you. I use them for high-speed bullets, bullets that would move so fast each frame they pass through targets by “stepping around” them in a given frame. By raycasting from where it is to where you are about to move it, you can find if you’re gonna hit anything.

EDIT: and to answer your actual question (my bad), from the Raycast you get back a RaycastHit2D, which is a structure that can tell you if you hit anything, as well as precisely the point of contact.

EDIT: reading Praetor’s reply below makes me think perhaps I misread your question OP. Be sure to chime in if nothing I’m saying makes sense!

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Dead reckoning. Have the projectile check how far it has moved each frame (or each FixedUpdate if it’s a Rigidbody).

Once it has moved the minimum required distance, deploy the web.

2 Likes
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Thanks for the replies. The Dead reckoning bit looks promising.