CODEWITHSUNDEEP
iosswiftscenekit
mike_t
mike_t

Reputation: 2691

Scenekit - physicsWorld setup to prevent kinematic nodes to intersect

I have several nodes in my scene which i can rotate and drag around. I've set up a physicsWorld delegate, added physicsBody with type kinematic to my nodes and check for physicsWorld didBeginContact - up to this point everything is ok, when i move the nodes , the contact begin/end fires.

The way i'm trying to handle this is to set a bool var that change to true once the contact start to prevent further movement, but i'm running into cases (especialy if i drag the node too fast) , that the node gets a little bit inside of the other object.

should i use different approach to this? I don't really want a collision, just the other node to act "solid" and not allow intersection even at higher speed contact.

EDIT:

Some sample images to further clarify the issue:

For simplicity i've added only 2 nodes to demonstrate the issue. First image is initial position, 2nd and 3rd (side view) are after a very fast pan to the right. The contact detection was fired only after nodes were already intersected.

One approach that I tried was grabbing the last position before the contact is triggered and reseting the node position after contact is detected, but the result is very choppy and unstable and for a split second you can sometimes see the objects intersecting anyway before jumping to the last "good" position. I feel there must be some easier way to achieve this, but after spending hours going through available resources i can't figure it out.

EDIT 2

further research pointed down the line of sweep testing, technicaly if i can detect possible collision before i move the node, i should be able to restrict the movement to stop before the intersetion occurs

UPDATE: another dead end, as Xcode points out

Error: convexSweep only works with convex shapes

Upvotes: 2

Views: 966

Answers (1)

mike_t
mike_t

Reputation: 2691

After a lot of days of headbanging and almost giving up, i re-re-reread the physicsWorld documentation and finally found what i was overlooking all the time - the contactTest method that can be manualy triggered at any time, independent of render loop. I use it in the renderer(_:willRenderScene:atTime:) in order to "fix" the overlap before the scene gets rendered.

My scene is bit more complicated than the example, but with few extra tweeks i almost got it working now. I'm not sure if this is the proper solution and how costy it will become performance wise, but for now i will settle down with this so i can move on with the development.

The relevant code in case somebody runs in similar situation:

func renderer(_ renderer: SCNSceneRenderer, willRenderScene scene: SCNScene, atTime time: TimeInterval) {

    // make sure we have active node and pan direction
    if(selectedBrickNode != nil && self.panDirection != nil){

        // contactTest
        let pw = scnScene.physicsWorld
        let node = selectedBrickNode.node!
        let contacts = pw.contactTest(with: node.physicsBody!, options: nil)

        var axisVector:SCNVector3
        // specify which axis we want to correct
        switch self.panDirection!{
            case "right","left": axisVector = SCNVector3Make(1,0,0)
            default: axisVector = SCNVector3Make(0,1,0);
        }

        for contact in contacts {
            // round contact normal to get a unit vector
            let cn = SCNVector3( round(contact.contactNormal.x),
                                 round(contact.contactNormal.y),
                                 round(contact.contactNormal.z))

            // fix only for pan direction axis
            if abs(cn.x) == axisVector.x && abs(cn.y)==axisVector.y  {
                let normal = contact.contactNormal
                let transform = SCNMatrix4MakeTranslation( round(normal.x) * -Float(contact.penetrationDistance),
                                            round(normal.y) * -Float(contact.penetrationDistance),
                                            round(normal.z) * -Float(contact.penetrationDistance))
                node.transform = SCNMatrix4Mult(node.transform, transform)
                // break to prevent repeated contacts 
                break;
            }

        }

    }
}

Upvotes: 4

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