Physics engine recommendation which can simulate pool game correctly?

Question

I'm making pool game like game. This game requires correct (or very accurate) reflective bounces. I tried Box2D and Bullet Physics, but they have this problem.

If there is a wall on top of this image, red line is regular course of the regular pool game. But the engines often shows green line course. Especially,

1. This happens after a ball moving slowly hits the wall.
2. Sometimes a ball moving fast get slower suddenly.

I'm finding a physics engine can simulate pool game as much as possible without these problems. Can you recommend some? I'm digging Newton Game Dynamics now, but I have no sure about this. I'm considering PhysX as next trial, and have to make my own if nothing be found. But it's obvious it'll take huge time, so I wish I will do not. I'll be very appreciated if you save my time. And of course, solution with Box2D / Bullet Physics are also welcomed!

Acceptable languages/platform are C/C++/Objective+C on iOS.

---

I attach my configuration with Box2D.

Walls

• static box shape
• linear/angular damping = 0.1
• restitution = 1.0
• friction = 100
• density = 10
• bullet = false
• fixed rotation = false
• inertial scale = 1.0

Balls

• dynamic sphere shape
• linear/angular damping = 0.1
• restitution = 1.0
• friction = 100
• density = 20
• bullet = true
• fixed rotation = false
• inertial scale = 1.0

Answer 1

Several solutions.

1. For Box2D, set b2_velocityThreshold in b2Settings.h file. In my case, I set it to 0.0f and it worked! Mass, friction, damping were NOT problem. Check this discussion thread for more details. http://www.box2d.org/forum/viewtopic.php?f=3&t=6906&p=30782#p30782

2. Using other physics engine. Newton Game Dynamics configured performing this correctly by default. However using Newton dynamics in iOS is possible but it's somewhat harder than others. I used several days configuring it for iOS.

I'm also asking on BulletPhysics forums. I'll update this when I got a solution.

-- (edit) --

There are some threshold attributes in Bullet, however I couldn't find exactly same thing with b2_velocityThreshold.

This looks similar, but didn't work well.

btRigidBody->setContactProcessingThreshold(0.0f)

Answer 2

Box2D will do what you want but you have to set the restitution (bounce) constants for the wall and ball fixtures. For a pool game you probably want to start with perfect restitution and high friction but linear and angular damping, and tweak from there.

Answer 3

Physics engines have a bounce threshold. I don't know how to do it in either of those engines, but the threshold being set too high will cause it to ignore impacts under a certain velocity. Lower the bounce threshold and it will bounce at lower speeds.

I know you asked for a different physics engine, but all physics engines I know of use bounce thresholds to keep objects from jittering when they're sitting on top of each other. So suggesting a good physics engine will be counterproductive as any good physics engine will have this effect.

Answer 4

I had this problem and for me the solution was providing perfect restitution.

So for me that is sqrt of 0.5 for all objects. Because sqrt(r1*r1 + r2*r2) == 1 in perfect situation.