sceneKit dynamic physic body fall through floor - ios

Question

I have a cube with dynamic physical body and a plane with kinematic physic body.When I place a cube above plane, it will fall onto plane and a bounce is expected.
The PROBLEM is: when the cube is small or light, it just go through plane.For instance, cube has 0.1*0.1*0.1 work fine but 0.05*0.05*0.05 sucks.In this case I still get physical body contacting notification.
this is my code for creating geometry:
//cube
//when dimension is 0.1 everything is fine
float dimension = 0.05;
SCNBox *cube = [SCNBox boxWithWidth:dimension height:dimension length:dimension chamferRadius:0];
cube.materials = #[material];
SCNNode *node = [SCNNode nodeWithGeometry:cube];
node.physicsBody = [SCNPhysicsBody bodyWithType:SCNPhysicsBodyTypeDynamic shape:nil];
node.physicsBody.mass = 1;
node.physicsBody.categoryBitMask = phsicBodyCategoryCube;
node.physicsBody.collisionBitMask = phsicBodyCategoryPlane;
node.physicsBody.contactTestBitMask = phsicBodyCategoryPlane;
//plane
self.planeGeometry = [SCNBox boxWithWidth:100 height:0.01 length:100 chamferRadius:0
plane.physicsBody = [SCNPhysicsBody bodyWithType:SCNPhysicsBodyTypeKinematic
shape: [SCNPhysicsShape shapeWithGeometry:self.planeGeometry options:nil]];
plane.physicsBody.categoryBitMask = phsicBodyCategoryPlane;
plane.physicsBody.collisionBitMask = phsicBodyCategoryCube;
plane.physicsBody.contactTestBitMask = phsicBodyCategoryCube;

Answer 1

I’m surprised you’re getting collisions at all. See the SCNPhysicsBodyType docs – the kinematic type is for bodies that you move (by setting their position, etc) to cause collisions, but that aren’t themselves affected by other bodies colliding with them.
If you set the floor’s type to static, you’ll probably see better results. A static body doesn’t move (either as a result of physics interactions, or by you setting its position), so the physics engine can more accurately check for other bodies colliding with it.
edit: Other things to look into:
Use a SCNPlane rather than a SCNBox for your floor. (Note that you can create physics bodies with shapes different from their visible geometry, if that helps.) I'm not sure about SceneKit's, but it's easier for a lot of physics engines to check "has some object passed this infinite boundary since the last frame?" than "is some object inside this finite region on this frame?"
Enable precise collision detection for your moving objects.

Answer 2

Finally I found this is all about SceneKit's physical simulation. If the cube falls too fast, It will make a large penetration with plane In physical simulation steps. In this case sceneKit just let it fall through plane instead of collision. When I change cube's velocity to a small value It collided with plane.
My solution is to give cube a upward velocity when large over-penetration happens, which is the 30% of fall velocity. The trick is adjusting cube's velocity until a collision happens.

Answer 3

Works only for spherical physics shapes
For this issue SCNPhysicsBody has special attribute: continuousCollisionDetectionThreshold
For example, in a game involving projectiles and targets, a small
projectile may pass through a target if it moves farther than the
target's thickness within one time step. By setting the projectile's
continuousCollisionDetectionThreshold to match its diameter, you
ensure that SceneKit always detects collisions between the projectile
and other objects.