Box2d - Object fixture restitution value affects odd bumping

[piotr.w...@gmail.com]

Hi, 

today i meed new problem with box2d library and creating objects with fixture restitution settings between 0 to 1. 

I have here minimal test case which creates new object into physic world:

   public static void createDefaultBodyWithFixture(float x, float y, float w, float h, float density, float friction, float restitution) {

        

        System.out.println("\nparameters: x:" + x + " y: "+ y 

                                + "   [ f: " + density 

                                + " d: " + friction 

                                + " r: " + restitution + " ] ");

        

        BodyDef bodyDef = new BodyDef();

        bodyDef.type = BodyType.DYNAMIC;

        bodyDef.position.set(x, y);

        Body dynamicBody = m_world.createBody(bodyDef);

        

        PolygonShape dynamicBox = new PolygonShape();

        dynamicBox.setAsBox(w, h);

        

        FixtureDef dynamicFixture = new FixtureDef();

        dynamicFixture.shape = dynamicBox;

        dynamicFixture.density = density;

        dynamicFixture.friction = friction;

        dynamicFixture.restitution = 0.001f;

        

        Fixture fix = dynamicBody.createFixture(dynamicFixture);

                

        System.out.println("params from body: x:" + dynamicBody.getPosition().x + " y:" + dynamicBody.getPosition().y  

                + "   [ f: " + fix.getFriction() 

                + " d: " + fix.getDensity() 

                + " r: " + fix.getRestitution() + " ] \n --------");

       

    }

when I run example on Java target I got this Output:

parameters: x:1.0 y: 2.0   [ f: 0.1 d: 0.1 r: 0.01 ] 

params from body: x:1.0 y:2.0   [ f: 0.1 d: 0.1 r: 0.01 ] 

 --------

parameters: x:3.0 y: 2.0   [ f: 0.2 d: 0.1 r: 0.11 ] 

params from body: x:3.0 y:2.0   [ f: 0.1 d: 0.2 r: 0.11 ] 

 --------

parameters: x:5.0 y: 2.0   [ f: 0.3 d: 0.1 r: 0.21000001 ] 

params from body: x:5.0 y:2.0   [ f: 0.1 d: 0.3 r: 0.21000001 ] 

 --------

parameters: x:7.0 y: 2.0   [ f: 0.4 d: 0.1 r: 0.31 ] 

params from body: x:7.0 y:2.0   [ f: 0.1 d: 0.4 r: 0.31 ] 

 --------

parameters: x:9.0 y: 2.0   [ f: 0.5 d: 0.1 r: 0.41 ] 

params from body: x:9.0 y:2.0   [ f: 0.1 d: 0.5 r: 0.41 ] 

 --------

parameters: x:11.0 y: 2.0   [ f: 0.6 d: 0.1 r: 0.51 ] 

params from body: x:11.0 y:2.0   [ f: 0.1 d: 0.6 r: 0.51 ] 

 --------

parameters: x:13.0 y: 2.0   [ f: 0.70000005 d: 0.1 r: 0.61 ] 

params from body: x:13.0 y:2.0   [ f: 0.1 d: 0.70000005 r: 0.61 ] 

 --------

parameters: x:15.0 y: 2.0   [ f: 0.8 d: 0.1 r: 0.71 ] 

params from body: x:15.0 y:2.0   [ f: 0.1 d: 0.8 r: 0.71 ] 

 --------

parameters: x:17.0 y: 2.0   [ f: 0.90000004 d: 0.1 r: 0.81 ] 

params from body: x:17.0 y:2.0   [ f: 0.1 d: 0.90000004 r: 0.81 ] 

 --------

parameters: x:19.0 y: 2.0   [ f: 1.0 d: 0.1 r: 0.90999997 ] 

params from body: x:19.0 y:2.0   [ f: 0.1 d: 1.0 r: 0.90999997 ] 

and I see something like this:

PlayN 1.8.5 

Thanks,

Piotr

[marcin...@gmail.com]

                                + "   [ f: " + density 

                                + " d: " + friction 

Output is confusing because of that...

Did you try to test it with the same density?

May you try with: The mass of a body is not adjusted when you set the density. You must call ResetMassData for this to occur.

body->ResetMassData();

Next: Restitution is combined using the following formula.

float32 restitution;

restitution = b2Max(shape1->restitution, shape2->restitution);

What is the restitution of the bottom-base element?

/lm

[piotr.w...@gmail.com]

Thanks, for that hint ... but it does not help :). 

I set density to the same value for each boxes and result is still the same. 

I realized that bumping change is visible between 0.8 to 1 restitution value. 

Here is video: http://youtu.be/1BoiDJvY0gY

/Piotr

[marcin...@gmail.com]

I realized that bumping change is visible between 0.8 to 1 restitution value. 

For me it match setting restitution to 0.8f in your `groundBody` - double check that.

[piotr.w...@gmail.com]

Hmmmm, I did some test and here are results:

ground body restitution: 0.01f  and dynamic bodies restitution from 0.7f to 1.0f:

The same restitution range for bodies bout ground restitution 1.0f affects that:

Thanks for figure out this "issue", I just need next time think about relations between bodies :).