Contributing

Vite has stricter rules than stock Unreal: no recursion, no new virtuals, no new Blueprint exposure, strict Clang compliance and absolute ABI stability. Read the guidelines before writing code, not before opening a pull request.

Vite exists because UE 4.27 can be made fast and stable. Contributions that compromise either defeat the point. The rules below are unusually restrictive for a game engine fork, and that is deliberate.

In this section

Topic	Covers
Coding Guidelines	Core principles, forbidden constructs, technical and performance rules
Commit Conventions	Prefixes, attribution, branch hygiene
Backporting	Bringing UE5 and upstream features into 4.27
Documentation	Contributing to these docs

Before you start

Read the coding guidelines. Several common C++ patterns are banned outright, and finding out after you have written the code is expensive. Check whether the change is already covered. The compile-time switches and engine default changes pages document a lot of existing work. Work on a branch. Push work-in-progress to alternative branches with a note on what remains, and make other forkers aware of it. Verify: compiles cleanly under MSVC, Clang compliant, no crashes on startup, shutdown or the Tech Showcase project, no log spam, no ABI changes. Work through the review checklist before opening the pull request.

The three rules that reject most pull requests

Do not modify ray tracing payload bitfields, shader-visible enums or flags, packed bitmasks used by RHI or RenderCore, reflection system bitmask definitions, or any CPU/GPU shared struct layout. Breaking these breaks PSO caching, ray tracing stability, serialization and cross-vendor GPU behaviour. ABI violations are rejected immediately, regardless of how good the rest of the change is. Changes are evaluated against an ARM-class ~1 GHz CPU baseline. Measuring on your desktop and finding it fast does not clear the bar. See Performance Targets. Contributions must be original work or permissively licensed (MIT, Apache 2.0, BSD, Zlib). Code copied from UE5 into a 4.27 fork sits under Epic's licence, which is a different question from a permissive licence — see Backporting.

What makes a good contribution

Contributions that fit Vite well tend to share a shape:

Measurable. A profiling capture before and after, on representative content, beats an argument.
Guarded. Anything not needed in shipping is behind a compile-time switch or a console variable, and off by default when it costs something.
Narrow. A change touching one subsystem is reviewable. A change touching the renderer, the physics layer and the build system is not.
Documented. New console variables, switches and defaults need a documentation page or a section in an existing one.

Getting set up

See Build from Source and Toolchain Requirements. Note that engine development requires a source build — installed builds cannot compile engine C++.