Can you make a CGI arrow for a bow in Hitfilm?

I was watching the behind the scenes of the Hobbit movies and the Avengers movies (I watch those in my free time) and I noticed Legolas' and Hawkeye's arrows are always CGI. They have the bow, but the arrows aren't ever there on set (for obvious reason), and sometimes even the string is CGI! Is it possible to take a 3D model of an arrow and rotoscope it to the bow of the footage? I wanted a character to have a bow in a short film I'm making, but decided against it due to safety reasons. There's always the problem of he can't dry-fire the bow (firing without an arrow) because that damages the bow but if I got a prop bow... Anyways would it be possible to do this with the arrows?


  • @HeySiri Absolutely! You can always look at stock footage first. Depending on what you want to do, that may be all you need. Otherwise, search for a 3D model of an arrow. I found this search...

  • @FilmSensei I could also theoretically track the part of the bowstring where the arrow attaches to (I do archery occasionally so I have a bow but I don't remember what the part is called) I may be able to do a little bit of tracking and some rotoscope tracking to then just automatically line the 3D model up, right?

  • @HeySiri I don't see why not, but it might just be faster to line it up manually. A track of a quick pull and fire probably wouldn't be more than a few frames, right?

  • @FilmSensei that's true. The next problem is how to have the actor "fire" the bow when the bow I have (I can't really afford a prop bow) is a real bow, and shouldn't be dry-fired because that's bad for it. How to make them look like they're releasing the string when they can't actually dry fire... any ideas?

  • @HeySiri My first thought is to train the actor to not actually pull on the string, but to pantomime it instead. It will take some practice because the instinct would be to pull the real string instead of an "air" string, but it shouldn't take long.

  • @CleverTagline could be done... but then how do I achieve the look of actually pulling a string in post? CGI it somehow?

  • @HeySiri Use a tweaked Lightning effect to make new "strings" for the bow, and probably the Wire Removal effect to get rid of the existing strings.

  • edited January 3

    @CleverTagline Sounds so far relatively simple just a bit tedious—how do I make the lightning effect act like a high tension string? I understand to apply both ends of the string to the end of the bow's limbs, but what about the part being pulled back?

  • @HeySiri I'd recommend using two instances of Lightning: one for the portion above the performer's fingers, and another for the part below it. Depending on how the scene is shot, you might be able to use HitFilm's 2D tracking to track the performer's hand and use that to drive a couple points, which could be used to drive the Lightning effects.

    If you feel you should see the the string between his/her fingers, add another short Lightning instance just for that and use masking to control its visibility between the fingers.

  • @CleverTagline sounds good! I will try this out and let you know how it goes here.

    Going to perform a quick test right now.

  • Triem23Triem23 Moderator

    Fricking heck, it took me forever to find this video!;

    Of course that's a crossbow, but it does show you can track in an arrow.

    The string and arrow aren't the issue (lightning was a great idea for the string). The problem is how are you going to get the bow to bend with the pull? I'll assume you're using a compound bow, not a recurve? If compound, well....yay, because with a recurve you'd have to deform the bow itself.

    Note on LOTR and Avengers, no the arrows are not ALWAYS CGI. Most of the time they are lightweight, practical props. Arrows are usually only CGI in scenes where they are actually fired - especially if the target is in frame - and quickly. Even when an arrow is fired the majority of the time theres a big padded target right out of frame (and the bow has been adjusted to a weaker pull. Maybe a 25lb pull, not 300).

    Usually it's a practical rig to NOT spend a lot of time adding in strings in post and adding arrows in post when a prop works as well (I've known a s few VFX supervisors in my time and the first thing they do on a show is try to figure out where to NOT use VFX).

    So, build a prop arrow from something like a thin plastic pipe (like a straw from a stupid Los Vegas "yard of booze" or a balsa dowel with a fake head. Something super-lightweight that would be nearly impossible to cause injury if mis-fired (a balsa wood arrow would sting, but it's gonna break itself before it penetrates anything) and use that. Minimise the VFX.

    Plus, with a prop, now your actors don't have to worry about an "air" string and keeping hands in the proper position, etc.

    Besides, if all the strings and arrows in Avengers were CGI then Hawkeye, "The Greatest Archer in the World" wouldn't have needed two (two!) arm-guards. Hawkeye should need NO arm-guard. Jeremy Renner had one week of coaching on archery and HE needed two arm-guards.


  • Glad someone asked, was thinking of asking myself, only I was too lazy. 

  • edited January 4

    @Triem23 I am using a recurve, and I didn't think of the limbs being pulled back... I don't think it'll be a practical idea for the movie unless they fire rubber arrows that I could mask out the blunt tip in post. I spent hours last night keyframing the arrow—not worth it in the end, although it still looks pretty cool. If you know how a bow actually works you know something is off when the limbs aren't being pulled back. Still, gave me a fun evening project.

    And @CleverTagline, the lightning strings work great! I just tracked my hand and the tips of the bow and it worked perfectly! Only rotoscoping for the bowstring was making it wobble after I released it, and that just took like fifteen seconds!

  • @Triem23 I'm attempting to use the Puppet Tool to animate the recurve bow's limbs. In a single frame, the animation looks quite good and I can move the limbs and a way that looks realistic. However, I now need to figure out this: how do I make the puppet's generated mesh move with the limb? I applied a keyframed mask to the limb, that moved with it, so that the only thing present on that layer is the limb, but the mesh stays place. Can I keyframe the mesh's position?

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