[Guide] Contact Listener

[nivangerow]

Now I have a jump function, I found out that the player can still "stick" underneath the block. Is there any way to detect where the two bodies are colliding?

[spaine]

Up. For my question on previous page.

Still don't know why my game closes on contact. It doesn't "force close" it just shuts down.

Thanks.

[ttttkk]

yes, it did shut down, but without error messages...

the problem is this line

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1. (x2.getUserData().equals("angel") || x1.getUserData().equals("enemy")

Parsed in 0.029 seconds, using GeSHi 1.0.8.4

[spaine]

yes, it did shut down, but without error messages...

the problem is this line

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1. (x2.getUserData().equals("angel") || x1.getUserData().equals("enemy")

Parsed in 0.030 seconds, using GeSHi 1.0.8.4

I still confused about contact listener, how should I go on with it?... do i need to use getBody() before getUserData()?

[MANISH KUMAR]

(x2.getUserData().equals("angel") && x1.getUserData().equals("enemy")

Solved

[Molkobain]

Hi, thanks for the tutorial. I followed it to handle jumps through "cloud" platform.

I'll put my code just in case someone wonders :

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1.                 final ContactListener contact = new ContactListener(){
2.                         @Override
3.                         public void preSolve(Contact contact, Manifold oldManifold){
4.                                 final Fixture x1 = contact.getFixtureA();
5.                         final Fixture x2 = contact.getFixtureB();
6.                         final float entityY;
7.                         final float obstacleY;
8.                        
9.                         if ( (x2.getBody().getUserData().equals(PLAYER_ID) && x1.getBody().getUserData().equals(CLOUD_ID)) ||
10.                                  (x1.getBody().getUserData().equals(PLAYER_ID) && x2.getBody().getUserData().equals(CLOUD_ID)) ){
11.                                 //We save player & block Y coordinates to see how contact is made
12.                                 if(x1.getBody().getUserData().equals(PLAYER_ID)){
13.                                         entityY = x1.getBody().getPosition().y;
14.                                         obstacleY = x2.getBody().getPosition().y;
15.                                 }else{
16.                                         entityY = x2.getBody().getPosition().y;
17.                                         obstacleY = x1.getBody().getPosition().y;
18.                                 }
19.                                 //If player jump though a "cloud" block, we let him pass only if he comes from below
20.                                 if(entityY >= obstacleY){
21.                                         contact.setEnabled(false);
22.                                 }
23.                         }
24.  
25.                         }
26.                        
27.                         @Override
28.                         public void postSolve(Contact contact, ContactImpulse impulse) {
29.                         }
30.                         @Override
31.                         public void endContact(Contact contact) {
32.                         }
33.                         @Override
34.                         public void beginContact(Contact contact) {
35.                         }
36.                 };
37.                 this.mPhysicsWorld.setContactListener(contact);
38.  

Parsed in 0.038 seconds, using GeSHi 1.0.8.4

[JimBadger]

This was the tutorial that got me to understand ContactListener, so thanks for that!

However, I have a problem...I can't seem to get my preSolve (or postSolve) methods to be called.

I'm using GLES2, and all the rest of my physics stuff is working perfectly, including stuff in beginContact and endContact.

I know there used to be a bug in GLES1 regarding preSolve, but I also know that was fixed. Is there anything special I need to to with GLES2 to get preSolve "working"? An updated library, or something?

Or, should I not be setting the contact listener on the actual physicsworld? Should I set contactlisteners on the actual objects? (Bearing in mind that the rest of my physics is working great....).

[ctlayon]

Thanks for a great guide on Contact Listener, I also found the last post by none other than skyuzo here, http://gamedev.stackexchange.com/questions/16943/how-to-remove-a-box2d-body-when-collision-happens, very helpful in addition to this guide!

[swatirawat]

can anyone give me an example of collision detection implemented between two dynamic bodies. I implemented the contact listener but i don't know how to check for collision. If i check collision between two sprites (using x.collideswith(y) ) , the collision is detected but the transparent space around the sprites is also considered as part of the collision. Can anyone help?

[OzLark]

@swatirawat this thread itself explains most of what you'll need.

This has been discussed here many many times, a little searching will find you lots of threads covering this topic.