[Kool]

Suppose I have the following entity:

 

EntityBase {
    id: platform
    entityType: "anEntity"

    width: 100;
    height: 100;

    BoxCollider {
        id: collider

        bodyType: Body.Dynamic
        collisionTestingOnlyMode: true

        categories: Box.Category1
        collidesWith: Box.Category2 | Box.Category3

        fixture.onBeginContact: {
           timer.start();

           if (contact begin with category 2) {

           }
           else {

           }
        }
        fixture.onEndContact: {
            if (contact end with category 2) {

            }
            else {

            }
        }
        fixture.onContactChanged: {
        	if (now contacting with category 1 and category 2) {

        	}
        }
    }
}

The collider states only contact with Category 2 and Category 3. Is there a quick and easy way to retrieve which category the entity is colliding with? I’m currently having to do the following:

        fixture.onContactBegin: {
            var fixture = other
            var body = other.getBody()
            var entity = body.target

            if (entity.entityType === "AnotherEntity") {
                // do something
            }
       }

This doesn’t feel clean and I’m wondering if there’s an easier way to get which category the entity is colliding with.

 

Cheers!

[GüntherFelgo Team]

Hi!
Good question! 😉

The information which Category (or even Categories) an entity collides with is not calculated automatically.
But you can easily retrieve this information yourself, as you have access to both fixtures of the involved entities.

For example, like this:

Scene {
 // ...
EntityBase {
      id: entity1 
      
      // ...

      BoxCollider {
        collidesWith: Box.Category1 | Box.Category3 | Box.Category4 | Box.Category7
        fixture.onBeginContact: {

          // this collider settings
          console.log("Fixture: "+fixture)
          console.log("Categories: "+fixture.categories)
          console.log("CollidesWidth: "+fixture.collidesWith)

          // other collider settings
          console.log("OFixture: "+other)
          console.log("Categories: "+other.categories)
          console.log("CollidesWidth: "+other.collidesWith)

          // check which categories collided
          var collidedCategories = fixture.collidesWith & other.categories
          console.log("collidedCategories: "+collidedCategories)

          // check for a specific category
          if(collidedCategories & Box.Category1)
            console.log("Category1")
          if(collidedCategories & Box.Category3)
            console.log("Category3")
          if(collidedCategories & Box.Category4)
            console.log("Category4")
           if(collidedCategories & Box.Category7)
            console.log("Category7")
        }
      }
    }

    EntityBase {
      id: entity2
      
      // ...

      BoxCollider {
        anchors.fill: parent
        bodyType: Body.Static
        categories: Box.Category2 | Box.Category3 | Box.Category5 | Box.Category7
      }
    }
}

 

You could also provide a function to be able to do the check quickly:

EntityBase {
      id: entity1
      
      // ...

      BoxCollider {
        id: collider
        collidesWith: Box.Category1 | Box.Category3 | Box.Category4 | Box.Category7

        function checkContactWith(other, category) {
          return fixture.collidesWith & other.categories & category
        }

        fixture.onBeginContact: {
          if(collider.checkContactWith(other, Box.Category1))
            console.log("Category1")

          // ...
        }
      }
    }

 

Cheers,
Günther

 

 

 

• This reply was modified 8 years, 1 month ago by  GT.

[Caeser]

Hi!

This is a good way to filter collisions, but what if i wanted to to know the entity properties of entityType,entityId, and variation when a collision happens.

How can I further dig for this information after finding out the category?

 

 

[Caeser]

When I to retrieve the information, of collideed fixture with the <i>other</i> argument. I get undefined arguments

 

Here is the Snippet

 

            fixture.onBeginContact: {


                var body = other.getBody();
                var collidedEntity = body.target;
                var collidedEntityType = collidedEntity.entityType;
                var collidedEntityId = collidedEntity.entityId;

                console.log("body",body)
                console.log("collidedEntity",collidedEntity)
                console.log("collidedEntityType",collidedEntityType)
                console.log("collidedEntityId",collidedEntityId)


                // check for a specific category
                if(checkContactWith(other, Box.Category4)){
                    enemys.destroy()
                }
                if (checkContactWith(other, Box.Category1)){
                    console.log("Hit Left Player: ",card_type)
                    
                   
                }
                if (checkContactWith(other, Box.Category2)){
                    console.log("Hit Right Player: ",card_type)
                   
              
                }

Application Out Put is

 

qrc:///qml/VPlay/physics/ColliderBase.qml:317:13: Unable to assign [undefined] to bool
qml: body Box2DBody(0x2c2fce08)
qml: collidedEntity QQuickRectangle(0x374b78e0)
qml: collidedEntityType undefined
qml: collidedEntityId undefined
qml: Hit Left Player:  0
qrc:///qml/VPlay/physics/ColliderBase.qml:317:13: Unable to assign [undefined] to bool
qml: body Box2DBody(0x2c2fce08)
qml: collidedEntity QQuickRectangle(0x374b78e0)
qml: collidedEntityType undefined
qml: collidedEntityId undefined
qml: Hit Left Player:  0
qrc:///qml/VPlay/physics/ColliderBase.qml:317:13: Unable to assign [undefined] to bool
qrc:///qml/VPlay/physics/ColliderBase.qml:317:13: Unable to assign [undefined] to bool
qml: body Box2DBody(0x37569930)
qml: collidedEntity Wall_QMLTYPE_184(0x374b7eb0, "wall_0")
qml: collidedEntityType wall
qml: collidedEntityId wall_0
qml: body Box2DBody(0x2c2fd1c0)
qml: collidedEntity QQuickRectangle(0x374b7a78)
qml: collidedEntityType undefined
qml: collidedEntityId undefined
qml: Hit Right Player:  1

 

Apart from that I keep getting this

qrc:///qml/VPlay/physics/ColliderBase.qml:317:13: Unable to assign [undefined] to bool

Every time I create a new entity.

[GüntherFelgo Team]

Hi Caeser!

Can you make sure that you derived your entities from EntityBase?

The output

qml: collidedEntity QQuickRectangle(0x374b78e0)

indicates that the collision happened with a plain QML Rectangle, which does not offer the entityType or entityId properties of EntityBase.

Let me know this helps!

Best,
Günther

[Caeser]

Hi Gunther,

I am actually using EntityBase

Here is my qml file sample

EntityBase {

    id:enemys
    entityType: "enemy_card" 
     

    Rectangle{

        id:card
        border.width: 2
        border.color: "#ffffff"
        x: cardX
        radius: 6
        y: cardY
        width: 50
        height: 70

        Text {
            id:  text1
            color: "#ffffff"
            text: cardText
            
        }

        Image {
            id: bottom_symbol
            width: 18
            height: 18
            x: 15
            y: 44
            source: symbolSource
        }

        BoxCollider {
            id:the_collider
            anchors.fill: card
            collisionTestingOnlyMode: false
            categories: Box.Category3
            collidesWith: Box.Category4 | Box.Category1 | Box.Category2
           friction: 0
            bodyType: Body.Dynamic
            bullet: false
            angularDamping: 0
            linearDamping: gameover ? 3 : 0
            fixedRotation: false


        }



    }




}// EntityBase

 

[GüntherFelgo Team]

Hi Caeser,

I see, thank you for the code!

While it is true that you are using EntityBase for the entity, the BoxCollider is parented to the Rectangle within the entity, which you get when accessing the other.getBody().target in the collision.

We recommend to always parent colliders to the entity (no additional items in the hierarchy between collider and entity), which also helps to avoid issues with collider and entity positioning. The representation of the collider within the physics world ignores any displacement applied by additional items in the hierarchy (e.g. the cardX and cardY settings are ignored by the physics world). You can verify this by setting PhysicsWorld::debugDrawVisible to true.

Best,
Günther