Question: I have the following code:

in my scene:

```
static const uint32_t enermyCategory    =  0x1 << 0;
static const uint32_t fatherCategory    =  0x1 << 1;

self.physicsWorld.contactDelegate = self;

    //init ship
Ship *ship = [Ship getFather];
ship.position = CGPointMake(CGRectGetMaxX(self.frame) - ship.frame.size.width , ship.frame.size.height);
[self addChild: ship];

    //init enermy
    Enermy *ene = [[Enermy alloc] initWithImageNamed:enermyName gameScene:self];
ene.position = ship.position;
[self addChild:ene];

#pragma mark - Physics Delegate Methods
- (void)didBeginContact:(SKPhysicsContact *)contact{
    NSLog(@"contact detected");
}

```

As you can see, I set both ship and energy at the same location to start with, so they will always collide.

For **both classes**, I have the following code in their init method:

```
//setup physics body
self.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:self.size];
self.physicsBody.dynamic = NO;
self.physicsBody.categoryBitMask = enermyCategory; #shipCategory for ship
self.physicsBody.collisionBitMask = 0;
self.physicsBody.contactTestBitMask = shipCategory; #enermyCategory for ship

```

What I found is that the **NSLog** is never get called, so that the physical collision detection never works, I've read a lot from apple developer tutorials and it seems all the same of what they had, not sure why is not working. **I can see the ship and energy images on screen collide each other**.

Answer: 
Try this..

```
<div class="container">
   <div class="col-xs-2">
      <div class="row">
            <div class="col-sm-6">
                <button type="button" class="btn btn-default">Button</button>
            </div>
            <div class="col-sm-6">  
                <button type="button" class="btn btn-default">Button</button>
            </div>
            <div class="col-sm-6">  
                <button type="button" class="btn btn-default">Button</button>
            </div>
            <div class="col-sm-6">  
                <button type="button" class="btn btn-default">Button</button>
            </div>
      </div>
   </div>
</div>

```

<http://bootply.com/106650>

**EDIT..**

To change the stack order, you'll want to nest the cols like this..

```
<div class="container">
   <div class="col-xs-3">
     <div class="col-md-6">
       <button type="button" class="btn btn-default">Button 1</button>
       <button type="button" class="btn btn-default">Button 2</button>
     </div>
     <div class="col-md-6">  
       <button type="button" class="btn btn-default">Button 3</button>
       <button type="button" class="btn btn-default">Button 4</button>
     </div>
   </div>
</div>

```

I updated the demo: <http://bootply.com/106650>
This is the base that will help you to achieve what you want to do. You may need some tweaks based on your specific screen sizes. You may also find more details at <http://getbootstrap.com/css/#grid-responsive-resets>

```
<div class="container">
    <div class="row">
        <div class="col-xs-3">
            <button type="button" class="btn btn-default">Button</button>
            <button type="button" class="btn btn-default">Button</button>
            <button type="button" class="btn btn-default">Button</button>
            <button type="button" class="btn btn-default">Button</button>
        </div>
    </div>
</div>

```

**UPDATE**

```
<div class="container">
    <div class="row">
        <div class="col-xs-3">
            <div class="col-md-6">
                <button type="button" class="btn btn-default">Button 1</button>
                <button type="button" class="btn btn-default">Button 2</button>
            </div>
            <div class="col-md-6">
                <button type="button" class="btn btn-default">Button 3</button>
                <button type="button" class="btn btn-default">Button 4</button>
            </div>
        </div>
    </div>
</div>

```