JBox2D - Find Collision Coordinates

Question

I am writing a Java program using JBox2D. I need to find the exact point of collision between the two textures, if and when they collide.

I have code to determine if a collision has occurred, and can obviously just call the collision object identifier to determine which textures are colliding.

What I cannot understand is how to capture the actual coordinates of the collision itself. I read the documentation, but it is very complicated and does not address this problem directly.

Here is my code:

import org.jbox2d.callbacks.ContactImpulse; import org.jbox2d.callbacks.ContactListener; import org.jbox2d.collision.Manifold; import org.jbox2d.common.Vec2; import org.jbox2d.dynamics.Fixture; import org.jbox2d.dynamics.contacts.Contact; public class MyContactListener implements ContactListener{ //When they start to collide public void beginContact(Contact c) { System.out.println("CONTACT"); Fixture fa = c.getFixtureA(); Fixture fb = c.getFixtureB(); Vec2 posA = fa.getBody().getPosition(); Vec2 posB = fb.getBody().getPosition(); } public void endContact(Contact c) { } public void preSolve(Contact c, Manifold m) {} public void postSolve(Contact c, ContactImpulse ci){} } 

Answer 1

To find out where the collision occurred, you need to know that sometimes there is not only one collision point, but also many points.

(Image extracted from this manual )

As indicated in this guide,

Box2D has functions for calculating contact points for overlapping shapes. [...] These points [...] group them into a structure of diversity. [...]

Normally, you do not need to directly calculate the contact collectors, however, you will probably use the result obtained in the simulation. [...] If you need this data, it is usually best to use the WorldManifold structure [...].

You can access it in the Contact c class:

 public void beginContact(Contact c) { System.out.println("CONTACT"); WorldManifold worldmanifold; worldmanifold = c.getWorldManifold(); for(Vec2 point : worldmanifold.points){ System.out.println("Contact at : [" + point.x + ", " + point.y "]"); } } 

It is important . I have never used this library (JBox2D), however I am familiar with it (since libGDX apparently uses a similar one (Box2D)). Also, I don't know if JBox2D is Box2D (C ++) for Java, and if JBox2D and Box2D (libGDX alone) are connected at all. Perhaps some methods may change ( point.x may be point.getX() ).

You can check this site , but this is for C ++ (I use their answer to answer you).