Mar
19
2013

Fast Projectiles

An article by mgear

Testing a script for fast moving projectiles (since normal physic objects always go through walls..)

Current version info:
– No colliders, rigidbodies or raycasts for the projectile
– Just move the objects inside FixedUpdate()
– Projectile gets the target point when clicked, it doesnt check collisions while flying..

There is also this, havent tested it yet: DontGoThroughThings
http://wiki.unity3d.com/index.php?title=DontGoThroughThings

Also physics settings could be adjusted:
http://docs.unity3d.com/Manual/class-PhysicsManager.html

See comments for more solutions..

—

Webplayer:
http://unitycoder.com/upload/demos/FastProjectiles/

Download source: (unity 4.1)
FastProjectiles.unityPackage (c#)

—

Here’s also modified test version of the unitywiki “DontGoThroughThings.js”
– Do a raycast from the previous position to the current position
– Then if raycast hits something, just stop (could set velocity to zero etc..)

#pragma strict
public var layerMask : LayerMask;
private var previousPosition : Vector3;
private var currentPositionRayTo : Vector3;
private var myRigidbody : Rigidbody;
private var hit : RaycastHit;

function Awake() {
myRigidbody = rigidbody;
previousPosition = myRigidbody.position;
}

//function FixedUpdate()
//function OnGUI()
function Update()
{
currentPositionRayTo = (transform.position-previousPosition);
//    Debug.DrawRay(transform.position, currentPositionRay, Color.green);
if (Physics.Raycast(previousPosition, currentPositionRayTo, hit, Vector3.Distance(transform.position, previousPosition), layerMask.value))
{
// we hit something, do stuff here (for example stop the force/speed/velocity, otherwise we would keep moving..)
//constantForce.enabled = false;
myRigidbody.position = hit.point;
}
previousPosition = myRigidbody.position;
}

Tags: collision, fast, physics, projectiles

About the Author:

.fi

15 Comments + Add Comment

John mathew 21/03/2013 at 14:57

Hi!,

First of all I would like to thank you for sharing all this ideas.

I have checked the wiki entry and it is the way I do this now. Would you mind commenting your method to do not use Raycasting? The other thing I would like to comment is that I do not understand why there is a need to do this all in FixedStep. At least for the wiki example. The FixedStep function will be called more times than Update method but in the wiki code it is raycasting from previous to current position, so why not to wait and do this once in the next Update?

Thanks in advance.

Reply
- mgear 21/03/2013 at 18:46
  
  Added the current source download.
  
  Not sure why DontGoThroughThings needs FixedUpdate(), tried with Update() also and it seems to miss the plane at some speeds where FixedUpdate() gets it.. made simplified test version of it, just do raycast from previous pos to current, if hit something then stop. Seems to work ok in few tests..
  
  Reply
- Marrt 26/03/2013 at 18:39
  
  DontGoThroughThings needs FixedUpdate() because it is working with Rigidbodys and Colliders and ONLY performs the raycasts if the movement of the rigidbody between two physics frames was great enough to surpass the attached Colliders extents.
  
  In every other case the normal collision detection of the Physics engine is enough. If you would put it into Update() i guess it could give some false positives if the frame rate is low – or wouldnt trigger at all if it is to high (>50) because the movement between 2 frames is never more than its extents
  
  However, i found it worked rather strange since the passing will happen anyway but one frame later the object is teleported back to the old position…. very bad if you use trailrenderers to smooth the projectiles apperance (the trail will go through the wall and then back to the raycast hitpoint). Therefore i modified it in my first implementations by forecasting to the next position if the velocity is great enough. Then it wont pass the wall and immediately is ported to the point (which is also bad because the teleport gives the projectile a velocity leap before it hits the wall)
  
  check my current solution below, it is way better but without colliders (=projectiles have no width)
  
  Reply
Marrt 26/03/2013 at 18:17

I also tinkered around with fast projectiles. What i ended up with is a kind of Raycast-interval.
it’s working great, only catch was that hitable objects moving against the projectile are prone to be missed (because: http://forum.unity3d.com/threads/134650-Rigidbody-Bullets)
so i use raycasts and additionally check if the position of the bullet is within a moving hitable object to counter that.

i sticked with FixedUpdate() for the framerate independence of the hit detection, it should be moveable to Update(). The Rigidbody is just a left over and can be converted to manual movement instead of velocity setting

so there are only a few cases where i occasionally fail to detect a hit:
-if the hitable object moves so fast that its discrete positions in fixed update don’t overlap (my game doesn’t allow that)
-if the object approaches the projectile in orthogonal direction (can be fixed with continous “contains” checks instead of conditional)

the script is somewhere in this project file:
http://forum.unity3d.com/threads/124019-SpaceNox-Working-Title/page3?p=1186317&viewfull=1#post1186317

“RaycastDestruction.cs” if i remember it right, but its overloaded with other stuff that allows projectiles to seek targets, bounce of walls and get slowed down by dampening fields

Reply
Terry Morgan 07/04/2013 at 20:18

Nice, arrows. I’ve been collecting projectiles, now I have 2 I like,

yours and this one

https://sites.google.com/site/terrymorgan1213/tutorials/ali-looqman-blaster

wondering if there’s a new/better/another way to switch weapons than in the Unity 3d FPS
tutorial from 2009.

https://sites.google.com/site/terrymorgan1213/tutorials/fps-tutorial-rocket-launcher

Reply
Mars 09/04/2013 at 01:16

I found your blog late last night and it has completely re-inspired me to continue working in/on Unity. I hope you don’t mind me stealing all of your source! XD

Reply
- mgear 09/04/2013 at 08:53
  
  thanks! no problems and feel free to post improvements/interesting links 🙂
  
  Reply
mgear 31/05/2013 at 23:26

“About collisions failing on high speed”
http://forum.unity3d.com/threads/184158-About-collisions-failing-on-high-speed

Reply
mgear 21/06/2013 at 02:02

physics trick switching between collision modes:
http://forum.unity3d.com/threads/187105-Handy-Physics-Trick

Reply
Simran 08/08/2014 at 08:55

Great article 😉
Here is my contribution.

Projectile to always hit a moving object: http://lexiconhub.tk/index/game-programming/projectile-motion-unity-3d/

Hope this helps 🙂
Thanks

Reply
mgear 08/12/2014 at 10:57

Unity realistic bullet ballistics (with example sources)

Reply
mgear 25/03/2015 at 13:13

Has anyone tried fast projectiles with Unity5?

“Collision detection

Continuous collision detection has been improved by an order of magnitude. Continuous collision detection is used to prevent fast-moving bodies from going through other bodies without any collisions detected. Imagine a bullet shot at a piece of paper, or a game of pool where some balls will move faster than others.

In Unity 5.0, the SDK generates all the data required to handle fast movement. You just enable continuous collision detection and it works. PhysX3 features an algorithm used to detect whether the expensive CCD simulation is actually needed given the current body velocity or a default discreet would do just fine. It’s activated once you enable the CCD.”

http://blogs.unity3d.com/2014/07/08/high-performance-physics-in-unity-5/

Reply
- Marrt 29/03/2015 at 15:13
  
  Hi mgear, has been some time since i did smth in Unity… i’m still chewing on serumas script every once in a while…
  
  However, i tried the Unity5 Collision detection and this is what i got:
  
  Shooting the target from front in line within its move direction:
  Barrel = – – – – Target
  
  -Discrete on Bullet(Fast) misses the Target(Slow) in any case
  -ContinuousBullet misses the Target if the target is not DynamicContinuous
  -DynamicContinousBullet hits the Target always, even if the target is moving very fast (more than its extents/frame)
  
  So Unity5 is totally capable of handling these now
  
  But when i shoot a target moving sideways fast it seems that Unity cannot detect collisions that would happen in between ph.frames if the moving directions are orthogonal to each other. But i have to make a better testsetup for this case.
  
  small sketch, these bullets should hit, but don’t
  o Bullet 1 pos1
  |
  |
  o Bullet 1 pos2
  <_| _o _ _o Bullet 2 pos1
  |
  o Bullet 1 pos3
  |
  |
  V
  
  Reply
Julian 10/04/2017 at 07:24

Could you re-upload the source somewhere? I would like to take a look at your technique, even if it won’t work in the latest version of Unity, but the link to download has ‘expired’.

Reply
- mgear 10/04/2017 at 12:10
  
  https seems to break the download links, ill fix that later this week.
  
  in the meanwhile you can download from
  http://unitycoder.com/blog/2013/03/19/fast-projectiles/
  
  Reply