Inside SwiftShot: Creating an AR Game

WWDC 2018

SwiftShot Internals

• Establishing a shared coordinate space
• Networking and state sharing
• Physics
• Asset import and management
• Flag simulation
• Dynamic audio

ARKit — Establishing a shared Coordinate Space

• Image detection
• Object detection
• World Map sharing
• iBeacons for fixed installations

Sharing a World Map

1. Saving

• First device scans area, captures features
• Asks ARSessionfor world map
• Serializes to dist

2. Ad-hoc gaming

Share over network

• Peer-to-peer network connnection
• Encrypt data in flight
• UI guidance to aid delocalization

3. Fixed installations

• Prerecord world maps for specific installation areas
• Distribute to managed devices
• Use iBeacons to automatically select correct world map for each location

4. Loading

5. Privacy

ARWorldMap uses features of the world around you

• No latitude/ longitude information
• May include personally identifiable information

Treat serialized ARWorldMap as user-private data

• Encrypt at rest and in motion
• Obtain user consent for extended usage

6. ARAnchor

ARAnchor represents a location and orientation in the physical world

• ARKit adds anchors for planes, objects, and images
• Also, created and added via API

Networking with Multipeer Connectivity

• Peer-to-peer connectivity, no central server
• Encryption and authentication are built in
• Advertisement and discovery
• Device starting the game creates a session, starts advertising
• Other devices see session listed in menu
• User selects game to join
  - Device sends request
  - Advertising device accepts or denies
• Once session set up, devices are peers in the network
• API to send
  - Data packets
  - Resources as URLs
  - Streams
• UDP for transport

Physics

• SceneKit physics
• All peers run physics simulation
• Server sends updates to client to ensure synchronization
• Only game state relevant information is shared
• Object scaled approximately 10x for better performance

Physics Data Optimization