XCOM 2 gameplay systems

1.

Gameplay Systems

2. XCOM EU vs. XCOM 2

– XCOM EU
• Game classes a mix of stock UE3 and custom Firaxis
– Not always appropriate, many side effects
• Visual presentation and gameplay mechanics intertwined
• Game elements hard-coded, strongly connected
– XCOM 2
• Game classes primarily custom Firaxis
• Presentation separated from gameplay mechanics
• Modular game elements

3. XCOM 2 Gameplay Systems Overview

Replay Manager
User Interface
Input
Player
AI Player
Game
State
Interface
Visualization
Manager
Observe
History
World &
Actors
Resolve
Rules
Engine
Validate
Submit
Submit
Build
Context
Network
Layer
History
Remote
Player

4. XCOM 2 User Interface & Input

XCOM 2 User Interface & Input
– Superficially similar to XCOM EU
– XComPresentationLayer forms the basis for UI
– Unreal Engine Player Controller and Input classes are still used
– Modular UI system allows screens to be constructed at run time.
– Created for rapid prototyping, debug UI, and mod support.
– Shipping UI generally does not use this system, but modular controls can be added /
removed to shipping screens.
– Many tactical UI elements recycled / reused from XCOM EU.

5. XCOM 2 Game State System Classes

History
– In XCOM 2’s Model View Controller setup
– The Game State System is the model
– Game State System Classes
– History
– Record of all game state changes
– Game State
– Also referred to as “History Frames”
– Game State Context
– Holds meta information about what changed
Game State
Context
…
…
StateObj
…
StateObj
…
StateObj
…
– Game State Object
– Represents a game entity, full copy of the latest state of that entity

6. XCOM 2 Game State System Basics

History
Game State
Game State
Tactical
Game Start
Std Move
BattleData
Map:
3x3 middle
blocked
Unit
TileLoc:
X=0 Y=0
– XCOM 2 sessions begin with a
start state.
Path:
X=0,Y=1
X=0,Y=2
X=1,Y=2
X=2,Y=2
Unit
TileLoc:
X=2 Y=2
Context:
Information on
how / what / why
State Object:
New state of a
particular game
entity
– Start states typically contain a
lot of state objects defining the
initial state for most of the
entities participating in the
session.
– Additional Game States / History
Frames define new states for
objects

7. XCOM 2 Game State System Basics

– The Game State system is persistent through map transitions.
– No more intermediate systems passing data when changing game modes.
Game State
Archive
Archive
History
XCOM HQ
Game State
Game State
Game State
Game State
Game State
Strategy
Game Start
HQ
Tactical
Orders
Game Start
Customize
XCOM
Soldier
Move
Geoscape
Alien
Interval
Move
Launch
Narrative
Battle
Moment
XCOM HQ
XCOM HQ
Alien HQ
BattleData
Time
Alien Unit
Unit
Unit
XCOM HQ
Time
Alien
Unit
Unit
Alien HQ
Time
Unit

8. XCOM 2 Game Ruleset

– Interface for gameplay systems that want to change game state
– Gameplay systems can read from the history directly.
– Tracks information such as ability availability, active player
– Subclasses provide game mode specific logic
– Tactical rule set implements interrupt logic, turn phases
– Multiplayer rule set includes turn timer, history serialization

9. XCOM 2 Game Ruleset : Tactical

10. XCOM 2 Visualization Manager

– Responsible for visualizing changes in the Game State system
– Controls Unreal Actors to depict state changes
– Strictly enforced data access
– Visualizers are not permitted to affect game state.
– The visualization manager must be able to operate from the History alone.
– Relies on Game State Context to drive visualization.
– The context contains the domain / state specific knowledge, so it builds the visualization
when requested.

11. XCOM 2 Visualization Manager

– Many visualizers are recycled from XCOM EU
– XGUnit & XComUnitPawn - XGItem & XComWeapon – XGPlayer
– Purely visual
– Core Visualization Manager Classes and Concepts
– Visualization Block – Corresponds 1 : 1 with a game state being visualized
– Visualization Track – Blocks have one track per state object in its associated game state
– X2Action ( or Track Action ) – Tracks are composed of a sequence of actions. X2Actions
make the visualizers run, shoot, step out of cover, etc. Many are recognizable as the
XGActions used by XCOM EU, but with gameplay logic removed.

12. XCOM 2 Visualization Manager

13. XCOM 2 Game State Feature Support

– Greater mechanical flexibility
– Chains of abilities and effects in EU were difficult to manage
– Since mechanics were bound to visuals, mechanics that required prediction were difficult
to impossible.
– Better debugging tools
– The game state history is navigable in-game via debug screen. Tracking down mechanical
issues is often as simple as reviewing the history.
– All saved games contain a full history. Saves are larger but can be used to analyze error
reports.

14. XCOM 2 Game State Feature Support

– Replay
– The visualization manager can operate on a ‘finished’ history to replay game sessions.
– Support for Replay brings other benefits
– Robust mechanics support in Multiplayer – if it works in SP it will work in MP. Clients take
turns building the history, and replaying remote updates to the history.
– On-rails tutorial support. Replay can operate in a “follow the leader” mode where the
replay UI looks identical to the normal UI, and is stepped forward by committing the next
user action in the history.
– Debugging: many bugs can be easily reproduced by loading a save provided by the QA
team and replaying it. While running in replay mode, the user can halt replay and resume
control at any point to reproduce issues that require input.

15. FIN