Physics Issue When Loading SCNScene from .dae - ios

Question

I am attempting to load a scene that is currently just 3 walls, a ceiling and a floor. I am loading the scene that I created in blender and load it in fine. However, a SCNNode with a geometry of a SCNBox just falls right through. The box has a dynamic physics body attached to it and the I am manually setting the walls/floor to be static nodes. Below is the code I am using to set up the scene and add the box, I can also post my .dae if needed. Anyone have any ideas as to what might be going on?
//Load the scene from file
SCNScene *scene = [SCNScene sceneNamed:#"mainScene.dar"];
//Get each node in the scene, and give it a static physics bodt
for (SCNNode *node in [[scene rootNode] childNodes]) {
SCNPhysicsBody *staticBody = [SCNPhysicsBody staticBody];
staticBody.restitution = 1.0;
node.presentationNode.physicsBody = staticBody;
NSLog(#"node.name %#",node.name);
}
//Create box
SCNNode *block = [SCNNode node];
block.position = SCNVector3Make(0, 0, 3);
//Set up the geometry
block.geometry = [SCNBox boxWithWidth:.8 height:.8 length:.8 chamferRadius:0.05];
block.geometry.firstMaterial.diffuse.mipFilter = SCNFilterModeLinear;
block.castsShadow = YES;
//Make it blue
for (SCNMaterial *mat in block.geometry.materials) {
mat.emission.contents = [UIColor blueColor];
}
//Add physics body
SCNPhysicsBody *body = [SCNPhysicsBody staticBody];
body.mass = 5;
body.restitution = .7;
body.friction = 0.5;
block.physicsBody = body;
//Add the node to the scene
[[scene rootNode] addChildNode:block];
In response to ricksters answer I tried to create custom geometry for each new node, but my box still falls through. Here is the code that I am using for the custom geometry. This replaces the for-in in the original code.
//Get each node in the scene, and give it a static physics bodt
for (SCNNode *node in [[scene rootNode] childNodes]) {
SCNGeometry *geometry = [SCNBox boxWithWidth:node.scale.x height:node.scale.y length:node.scale.z chamferRadius:0.0];
SCNPhysicsShape *physicsShape = [SCNPhysicsShape shapeWithGeometry:geometry options:nil];
SCNPhysicsBody *staticBody = [SCNPhysicsBody bodyWithType:SCNPhysicsBodyTypeStatic shape:physicsShape];
staticBody.restitution = 1.0;
node.physicsBody = staticBody;
}

Answer 1

So I had a similar issue. I found that the issue stemmed from how the file was created in the 3d modeling software. I was using Blender to test this; I made a plane with a box, added a physics body to the box and the plane and the box fell through. I realized this had to do with the scale. In Blender, I applied the object transformation which reset the scale to 1.0 1.0 1.0 by pressing CTRL A and selecting the scale option. So ultimately what seems to be happening is that SceneKit uses the base geometry ignoring the transform of the geometry. What you are seeing on the screen is the base geometry with the node's transform applied. Set the transform to identity before exporting the Collada file and you should be set.

Answer 2

Depending on how the geometry for those nodes is built in the DAE, SceneKit may not be able to automatically construct a physics shape that does what you want.
Instead, use bodyWithType:shape: to create exactly the collision shape you want, separate from the node's visible geometry. Creating physics shapes from parametric geometry (e.g. SCNBox, SCNSphere) works best.