spacetris/.copilot-rules.md

Copilot Rules — Spacetris (SDL3 / C++20)

These rules define non-negotiable constraints for all AI-assisted changes. They exist to preserve determinism, performance, and architecture.

If these rules conflict with .github/copilot-instructions.md, follow .github/copilot-instructions.md.

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Project Constraints (Non-Negotiable)

• Language: C++20
• Runtime: SDL3 + SDL3_ttf
• Build system: CMake
• Dependencies via vcpkg
• Assets must use relative paths only
• Deterministic gameplay logic is mandatory

Do not rewrite or refactor working systems unless explicitly requested.

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Repo Layout & Responsibilities

• Core gameplay loop/state: src/Game.*
• Entry point: src/main.cpp
• Text/TTF: src/Font.*
• Audio: src/Audio.*, src/SoundEffect.*
• Effects: src/LineEffect.*, src/Starfield*.cpp
• High scores: src/Scores.*
• Packaging: build-production.ps1

When adding a module:

• Place it under src/ (or an established subfolder)
• Register it in CMakeLists.txt
• Avoid circular includes
• Keep headers minimal

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Build & Verification

Prefer existing scripts:

• Debug: cmake --build build-msvc --config Debug
• Release:
  • Configure: cmake -S . -B build-release -DCMAKE_BUILD_TYPE=Release
  • Build: cmake --build build-release --config Release
• Packaging (Windows): ./build-production.ps1

Before finalizing changes:

• Debug build must succeed
• Packaging must succeed if assets or DLLs are touched

Do not introduce new build steps unless required.

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Coding & Architecture Rules

• Match local file style (naming, braces, spacing)
• Avoid large refactors
• Prefer small, testable helpers
• Avoid floating-point math in core gameplay state
• Game logic must be deterministic
• Rendering code must not mutate game state

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Rendering & Performance Rules

• Do not allocate memory per frame
• Do not load assets during rendering
• No blocking calls in render loop
• Visual effects must be time-based (deltaTime)
• Rendering must not contain gameplay logic

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Threading Rules

• SDL main thread:
  • Rendering
  • Input
  • Game simulation
• Networking must run in a separate thread
• SDL main loop must never block on networking
• Cross-thread communication via queues or buffers only

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Assets, Fonts, and Paths

• Runtime expects adjacent assets/ directory
• FreeSans.ttf must remain at repo root
• New assets:
  • Go under assets/
  • Must be included in build-production.ps1

Never hardcode machine-specific paths.

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AI Partner (COOPERATE Mode)

• AI is supportive, not competitive
• AI must respect sync timing and shared grid logic
• AI must not “cheat” or see hidden future pieces
• AI behavior must be deterministic per seed/difficulty

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Networking (COOPERATE Network Mode)

Follow network_cooperate_multiplayer.md.

Mandatory model:

• Input lockstep
• Transmit inputs only (no board state replication)

Determinism requirements:

• Fixed tick (e.g. 60 Hz)
• Shared RNG seed
• Deterministic gravity, rotation, locking, scoring

Technology:

• Use ENet
• Do NOT use SDL_net or TCP-only networking

Architecture:

• Networking must be isolated (e.g. src/network/NetSession.*)
• Game logic must not care if partner is local, AI, or network

Robustness:

• Input delay buffer (4–6 ticks)
• Periodic desync hashing
• Graceful disconnect handling

Do NOT implement:

• Rollback
• Full state sync
• Server-authoritative sim
• Matchmaking SDKs
• Versus mechanics

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Agent Behavior Rules (IMPORTANT)

• Always read relevant markdown specs before coding
• Treat markdown specs as authoritative
• Do not invent APIs
• Do not assume external libraries exist
• Generate code file by file, not everything at once
• Ask before changing architecture or ownership boundaries

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When to Ask Before Proceeding

Ask the maintainer if unclear:

• UX or menu flow decisions
• Adding dependencies
• Refactors vs local patches
• Platform-specific behavior