Algorithm: If passed between other two

Hi guys

Imagine a billiards like game. There are 3 balls. Even though game is 3D we are working only on x and z axis.

What i want to know is "how can i know, if a player hit a ball and that ball passed between the other two balls".

I have tried 5-6 algorithms. Took my many days and still failed.

I can save all three balls positions at each update, or at each time a collision happens for calculation purposes.
I can know if hitted ball passed other side of the arena(split from an imaginery line by other two balls), dynamically
I can know if two line segments collide(given four positions)
I can know the collided point of two line segments

I have tried algorithms that uses different combinations of these(mentioned above) to find a solution. But most causes mistakes at some extreme situations. The biggest problem i have encountered is, when a ball hits another ball. That ball moves at the same time with hitted ball, which causes many problems for different algorithms.

I couldn't come up with a good algorithm, can you help?

Thanks in advance.

 

Cast a Ray from ball 1 to ball 2. If ball 3 interrupts this ray, call your "PassedBetween" function.

http://docs.unity3d.com/ScriptReference/Physics.Raycast.html

 

Is it safe? What if the frame drops and ball just passes without not being able to be detected?

Just because of this fear i did not used that.

 

Raycasts should happen in FixedUpdate, so frame drops wouldn't be an issue.

Even if they were, a single raycast every frame is pretty cheap.

 

Thanks for the reply.

How could i forgot FixedUpdate. Something is not right with me. I should get proper sleeps

I will go make some tests with it.

 

Even in fixed, a fast moving ball can still jump past a ray.
If it were me, I'd do one of 2 options

• Put a collider inbetween the gate balls. Its on a layer that the balls dont collide with. cast ray from the moving ball, the distance that it moves in the frame to detect this collider.
• 2d line intersection maths. gate balls form a line segment, moving ball distance travelled in a frame makes the other line segment.

 

I have made some tests and what you said is true.

Since this is a crucially important feature of the game. I have decided to use line intersections and some other geometric formulas. I just finished a new algorithm and was thinking of how to implement it. This new algorithm i made seems good enough. I will make some tests after i finished implementing it.

Thanks for your answers. It really did helped me a lot.