Unity3d Billiard/Pool aiming issue

Question

I'm trying to calculate what angle to hit a pool ball and predict where ball will go to.. I thought target ball should move within a normal direction.. but it moves on totally different direction

RaycastHit2D hit = Physics2D.CircleCast(cue.position, _radius, dir, 100f, ~(ignoreLayer));
if (hit.collider != null)
{
    Debug.DrawRay(hit.collider.transform.position, -1f * hit.normal, 
    Color.green, Time.fixedDeltaTime);
}

Here is result:

enter image description here

Set velocity

rb.velocity = dir * force;

Result:

enter image description here

How to find exact move direction, Thanks

Edit:

I have tried Double Radius Casting this works only half way.. only when ray inside inner circle

we can set this for target ball OnCollisionEnter2D, manually change targeting ball velocity.. but this is kind of cheating..) I think(hopefully) there are move intuitive way to achieve this.. thanks @FredrikWiderberg — wrRios, Jun 16 '18 at 11:09
It is dependent on a number of properties, including i) the (ratio of) masses of the balls, ii) the coefficient of resistution between the balls (1 = elastic collision), iii) friction between the balls (which leads to angular momentum transfer) and iv) whether you take spin into account (as a direct result of iii)) — meowgoesthedog, Jun 16 '18 at 15:17
did u set the physics material on the balls to zero friction and zero bounciness? — Lincoln Cheng, Jun 19 '18 at 04:41
@LincolnC Yes also I have tried to set everything to zero, keep default settings and many more.. — wrRios, Jun 19 '18 at 05:22
Anyone please.. With double radius We can predict 100% only when ray is inside ball.. but direction still wrong when on casting outside http://prntscr.com/jwp62v — wrRios, Jun 19 '18 at 12:02
If you don't mind sharing all your C# scripts and screenshots of your Unity project settings, I can try it out myself. Between the two, there are so many variables that you might need to share a little more of your project to make the issue reproducible. — K Man, Jan 27 '19 at 13:20
In newer versions of Unity you can apparently use multiple Physics Scenes to precisely determine the outcome. Take [this video](https://www.youtube.com/watch?v=DcGiUcfLbes) of drawing the trajectory of a ball, for instance. — Philipp Lenssen, Aug 06 '19 at 10:40
heres one old test project also, i think it worked fine there https://github.com/unitycoder/Snooker2D — mgear, Feb 16 '21 at 08:19

score 0 · Answer 1 · answered Apr 18 '20 at 11:35

I suppose this is just a limitation of the physics engine, which is optimized for speed and use in games, and is not so exact.

Trying this myself in a simple 2D scene, I found that if I set the friction to 0.01 and the bounciness to 1.0, it works the way I would expect. (in Unity 2020.1)

In the small sample scene I added, there is a ball aiming at another so that the resulting angle should be 45 degrees. And after setting the phyics-mat to the properties with friction 0.01 and bounciness 1.0, the resulting angle is as expected.

With the default-mat I get the same behaviour you described.

Did you forget to assign the physics materials?

Have you single-stepped to the point of contact and checked if the aiming is correct?

my sample project trying this

Unity3d Billiard/Pool aiming issue

1 Answers1