[phil.jahoda]

Hi.

In our game, its the players task to shoot arrows to pop baloons. Therefore I have to check when the arrow hits a baloon.

I do that within the fixture.onBeginContact(….) method where I then make the baloon disappear.

The problem is, that as soon as the arrow hits the baloon, it bounces from it. But that should not happen because I want the arrow to continue flying its original direction. How can I stop it from bouncing of a baloon?

As our pysicsworld also uses gravity.y, I have to make the Baloon BoxCollider BodyType.Static to keep it from falling.

I already tried setting vairous properties to zero, it didnt help.

[phil.jahoda]

Here is my Baloon.qml, I am sorry, the code tag does not seem to work.

import QtQuick 1.1
import Box2D 1.0
import VPlay 1.0
import "../particles"

EntityBase {
  id: entity
  width: 20
  height: 25
  entityType: "baloon"
  
  property alias baloonImg: baloonImg
  
  BoxCollider {
    id: boxCollider
    bodyType: Body.Static
    width: baloonImg.width
    height: baloonImg.height
    
    // like this, an offset for the rotation could be set which is only applied for the collider, not for the entity!
    // rotation: 45
    
    anchors.centerIn: parent
    
    // set friction between 0 and 1
    fixture.friction: 0
    // restitution is bounciness
    fixture.restitution: 0
    // if you want to make objects fall faster, increase gravity (and not density)
    // with higher density, the player behaves differently at collisions as it is heavier
    fixture.density: 0
    
    fixture.onBeginContact: {
      
      var fixture = other;
      var body = other.parent;
      var component = other.parent.parent;
      var collidedEntityType = component.owningEntity.entityType;
      
      var collidingType = component.owningEntity.entityType;
      // play the collision sound when the box collides with anything, but not if the sound is already playing
      if(scene.collisionSoundsEnabled && !collisionSound.playing)
        collisionSound.play();
      
      if(scene.particlesEnabled)
        collisionParticleEffect.start();
      
      if(collidingType === "dartarrow" ) {
        entity.removeEntity();
        
        return;
      }
    }
  }
  
  Image {
    id: baloonImg
    source: "../img/baloon_green.png"
    // this is the size compared to the scene size (480x320) - it will automatically be scaled when the window size is bigger than the scene
    // the image will automatically be scaled to this size
    width: 20
    height: 25
    
    // this is required to have the center in the middle of the enity and not the top left point as origin of the image
    anchors.centerIn: boxCollider
  }
  
  // gets played at a collision
  Sound {
    id: collisionSound
    source: "../snd/boxCollision.wav"
  }
  
  // this particle effect is played when colliding with an obstacle
  SmokeParticles {
    id: collisionParticleEffect
  }
}

[ChristianFelgo Team]

Hi,

we are sorry for inconveniences with the Code button and working on a fix for it!

Regarding your Box2D question:

You could use the sensor property of BoxCollider for your use-case.By setting it to true, you still get notified when a collision occurs, but the other bodies do not physically react to the collision. Does that solve your problem?

 

Cheers,

Chris

[phil.jahoda]

I do not completely understand why, but yes this solves my problem.

Thank you very much!

[ChristianFelgo Team]

Hi again,

from the Box2D manual section 6.3 about sensors which is available here:

Sometimes game logic needs to know when two fixtures overlap yet there should be no collision response. This is done by using sensors. A sensor is a fixture that detects collision but does not produce a response.

Maybe that explains the topic best.

Cheers, Chris