Requirements and game rules in LLD - System Design Guide

Problem Statement

When building a game, unclear or incomplete requirements cause confusion and errors during development. Without well-defined game rules, players experience inconsistent gameplay and frustration, leading to poor user satisfaction.

Solution

Clearly defining requirements and game rules upfront ensures all developers understand the expected behavior. This includes specifying game objectives, player actions, scoring, and win/loss conditions. Well-documented rules guide both development and testing, creating a consistent player experience.

Architecture

Requirements

→Game Rules

↓

Player Input

Player Input

This diagram shows how requirements lead to defining game rules, which the game engine uses to process player input and control gameplay.

Trade-offs

✓ Pros

→

Prevents misunderstandings by providing a clear development guide.

→

Ensures consistent gameplay experience for players.

→

Facilitates easier testing and debugging with defined expected behaviors.

→

Improves communication among team members.

✗ Cons

→

Requires upfront time investment to gather and document requirements.

→

May limit flexibility if rules are too rigid and not adaptable.

→

Incomplete or ambiguous rules can still cause confusion.

Always use when developing any game or interactive system where player experience depends on consistent rules and behavior.

Not applicable to purely experimental or prototype projects where rules evolve rapidly and formal documentation is unnecessary.

Real World Examples

Nintendo

Defines clear game rules for titles like Mario to ensure consistent player objectives and controls across versions.

Epic Games

Uses detailed requirements and rules in Fortnite to balance gameplay and maintain fairness among millions of players.

Blizzard Entertainment

Documents precise game mechanics and rules in Overwatch to support competitive play and regular updates.

Code Example

The before code lacks defined rules like scoring or game over conditions, causing inconsistent behavior. The after code encapsulates game rules in a class, tracking score and lives, ensuring consistent gameplay logic.

LLD

### Before: No clear rules, logic scattered
class Game:
    def play(self, action):
        if action == 'jump':
            print('Player jumps')
        elif action == 'shoot':
            print('Player shoots')
        # No win/loss conditions or scoring

### After: Clear rules and requirements implemented
class GameRules:
    def __init__(self):
        self.score = 0
        self.lives = 3

    def apply_action(self, action):
        if action == 'jump':
            print('Player jumps')
        elif action == 'shoot':
            print('Player shoots')
            self.score += 10

    def check_game_over(self):
        return self.lives <= 0

class Game:
    def __init__(self):
        self.rules = GameRules()

    def play(self, action):
        self.rules.apply_action(action)
        if self.rules.check_game_over():
            print('Game Over')
        else:
            print(f'Score: {self.rules.score}')

Alternatives

Agile Iterative Development

Focuses on evolving requirements and rules through player feedback rather than upfront complete definitions.

Use when: When rapid changes and player-driven design are prioritized over initial completeness.

Prototyping

Builds a minimal playable version first to explore rules before formalizing requirements.

Use when: When the game concept is new or uncertain and needs early validation.

Summary

Clear requirements and game rules prevent confusion and inconsistent gameplay.

They guide development and testing to create a reliable player experience.

Defining them upfront saves time and improves communication among developers.

Practice

1. What is the main purpose of requirements in game design?

easy

A. To describe what the game must do

B. To explain how players should play

C. To decide the game's graphics style

D. To set the game's price

Solution

1. Step 1: Understand the role of requirements

   Requirements define the features and functions the game must have to work properly.

2. Step 2: Differentiate from rules

   Rules tell players how to play, not what the game must do technically.

3. Final Answer:

   To describe what the game must do -> Option A

4. Quick Check:

   Requirements = what game must do [OK]

Hint: Requirements = what game must do, rules = how to play [OK]

Common Mistakes:

• Confusing requirements with rules
• Thinking requirements set player behavior
• Mixing technical needs with gameplay instructions

2. Which of the following is a correct way to write a game rule?

easy

A. The game must load in under 5 seconds

B. Players must collect 10 coins to win

C. Use a database to store player scores

D. The game engine should support 3D graphics

Solution

1. Step 1: Identify what a game rule is

   A game rule tells players what they must or must not do during play.

2. Step 2: Check each option

   Players must collect 10 coins to win is a player instruction (rule). Options B, C, D are technical requirements.

3. Final Answer:

   Players must collect 10 coins to win -> Option B

4. Quick Check:

   Rules = player instructions [OK]

Hint: Rules tell players what to do, not technical details [OK]

Common Mistakes:

• Confusing technical requirements with rules
• Writing rules as system features
• Ignoring player actions in rules

3. Given these statements, which one is a requirement rather than a rule?
1. Players can jump over obstacles.
2. The game must save progress automatically.
3. Players lose a life if they touch spikes.
4. The game ends after 3 levels.

medium

A. The game must save progress automatically

B. Players lose a life if they touch spikes

C. Players can jump over obstacles

D. The game ends after 3 levels

Solution

1. Step 1: Identify requirements vs rules

   Requirements describe system features; rules describe player actions and consequences.

2. Step 2: Analyze each statement

   Statement 2 is a system feature (requirement). Others describe player actions (rules).

3. Final Answer:

   The game must save progress automatically -> Option A

4. Quick Check:

   Requirement = system feature [OK]

Hint: Requirements = system features; rules = player actions [OK]

Common Mistakes:

• Mixing player actions with system features
• Choosing rules as requirements
• Ignoring automatic system behaviors

4. A game designer wrote this rule: Players must collect 5 coins to win. But players can win without coins. What is the likely problem?

medium

A. The game has too many levels

B. The requirement is missing

C. The rule is not enforced in the game logic

D. The game has a syntax error

Solution

1. Step 1: Understand the problem

   The rule says players must collect coins, but they can win without doing so.

2. Step 2: Identify cause

   This means the game logic does not enforce the rule properly.

3. Final Answer:

   The rule is not enforced in the game logic -> Option C

4. Quick Check:

   Rule enforcement = game logic implementation [OK]

Hint: If rule ignored, check game logic enforcement [OK]

Common Mistakes:

• Confusing missing requirement with rule enforcement
• Assuming syntax error causes rule failure
• Ignoring game logic role

5. You want to design a fair multiplayer game. Which combination best ensures fairness and fun?

hard

A. Flexible rules with no system requirements

B. Complex rules that confuse players and minimal system requirements

C. No rules but strict technical requirements

D. Clear rules for player actions and balanced requirements for system performance

Solution

1. Step 1: Define fairness and fun

   Fairness needs clear rules; fun needs smooth system performance (requirements).

2. Step 2: Evaluate options

   Clear rules for player actions and balanced requirements for system performance combines clear player rules and balanced system needs, ensuring fairness and fun.

3. Final Answer:

   Clear rules for player actions and balanced requirements for system performance -> Option D

4. Quick Check:

   Fairness + fun = clear rules + balanced requirements [OK]

Hint: Fair game = clear rules + balanced system needs [OK]

Common Mistakes:

• Choosing complex or missing rules
• Ignoring system performance impact
• Separating rules from requirements