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Engine Coding Guidelines

Core Principles

Stability first.

Code must remain predictable and safe under both MSVC and Clang.

Performance-focused.

All changes must consider CPU, GPU, and memory impact, with ARM-class ~1 GHz CPU as a baseline target. Performance measured on a local desktop CPU must not be treated as sufficient or representative of real-world target hardware.

Strict Clang 16+ compliance.

No MSVC-specific behavior, compiler extensions, or undefined constructs.

Licensing clarity.

All contributions must be copyright-clean. Code may be included only if it is:

  • Original work by the contributor or

  • Licensed under permissive licenses (e.g. MIT, Apache 2.0, BSD, Zlib)

ABI safety.

Do not modify engine bitmask layouts, payload structures, serialization formats, or any CPU/GPU-shared binary contracts.

Forbidden Usage

  1. Recursion

  • Recursion is banned; use iterative patterns.

  1. No virtual functions

  • Do not add new virtuals unless strictly required.

  1. Kismet/Blueprint API additions

  • No new BlueprintCallable or BlueprintPure functions unless explicitly approved.

  1. Template usage avoidance

  • Avoid templates unless they provide a clear performance or architectural benefit.

  • Do not introduce template-heavy patterns that increase compile times, binary size, or code complexity.

  1. ABI-breaking modifications Do NOT modify:

  • Ray tracing payload bitfields

  • Shader-visible enums or flags

  • Packed bitmasks used by RHI or RenderCore

  • Reflection system bitmask definitions

  • Any CPU/GPU shared struct layouts

Such modifications break PSO caching, ray tracing stability, serialization, and cross-platform/vendor GPU behavior.

Commit Naming

Use the following Prefixes:

[Optimization]
[Rendering Feature]
[VR]
[Mobile]
[Plugin]
[Fix]

When making backports or adding a plugin, include the correct links to original commits/repos.

Technical Standards

  1. No undefined behavior or non-standard extensions.

  2. Avoid implicit type conversions.

  3. Maintain memory correctness: avoid large stack allocations, minimize dynamic memory

  4. Prefer constexpr, FORCEINLINE, and zero-cost abstractions.

Performance Rules

  1. Favor contiguous memory and cache-friendly layouts.

  2. Avoid unpredictable branching in hot paths.

  3. No FString processing, reflection calls, dynamic allocation, or virtual dispatch inside per-frame loops.

  4. Use SIMD-friendly math (SSE/AVX/NEON) when appropriate.

WIP work/Branches

  1. Commit to alternative branches to pass WIP work

  2. Give a brief commentary on what’s left to be done

  3. Delete unnecessary temporal branches

  4. Make other forkers aware of the WIP work

Verification Requirements

  1. Compilation

  • Must compile cleanly under MSVC and be Clang compliant.

  1. Stability

  • No crashes on startup, shutdown, or on the Tech Showcase project.

  • No log spam.

  • Guard all code not necessary for shipping

  1. ABI

  • All shader-visible structs must remain bit-for-bit identical.

  • No changes to payloads, bitmask layouts, uniform buffers, or reflection flags.

  • ABI violations result in immediate rejection.

Review Checklist Before PR, one must confirm:

  • No recursion

  • No added virtual calls (and cache existing engine virtuals where possible)

  • No new Kismet exposure

  • Copyright-free code

  • ABI and bitmask integrity preserved

  • Strict Clang compliance

  • No undefined behavior

  • No performance regressions

  • No unnecessary binary size increases

  • No shader or RHI ABI mismatches

13 January 2026
Technical DocumentationEngine Systems