taffy_cpp — Taffy C++ port

❗ This project currently in 'Work In Progress' state ❗

Web Playground

This library is a port of excellent Rust-written Taffy UI layout library for C++.

The main goals of this library are:

• Provide all the features (or almost all) of the Taffy library (with similar API) but for C++ projects.
• Behave exactly like Taffy and pass all tests.
• Be the same fast and achieve same cross-platform support (or even wider).

If you can use Taffy (if your project written in Rust, or can be easily linked with it) - you should use it! If you can't (for example: if your project in C++, and you want to use Taffy 'directly' - without linking or wrapping) - taffy_cpp for you! :)

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In short - taffy_cpp is a 'mirror', 'reflection' or 'back-port' of Taffy library, to provide ability of usage of it's brilliant algorithms in other (non-Rust) environments or toolchains.

If you want to add any feature or bug-fix - first of all propose changes into Taffy project. If they are accepted, next (if it's possible) - they will be ported into taffy_cpp. This project aims to be a 'reflection' of Taffy (and be compatible and similar to it as close as possible), not a separated incompatible standalone entity. In taffy_cpp considered only changes that improve code similarity (with Taffy) or improve performance and safety.

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If you find taffy_cpp useful for you, you can show it in a simple way - just put a 'star' ⭐ for this project on GitHub. Instead of saying thanks, this way you will show that this project is in demand, and you can also see how many of the same users need it.

Don't forget to add the Taffy 'star' ⭐ too! The great work in that repository is the reason why taffy_cpp even exists.

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Notice, that Taffy in the future may have FFI interface (exposing its API via C interface - for bindings with other languages), and gccrs & rustc_codegen_gcc developing promisingly, but taffy_cpp still may be needed for those, who prefer simple C++ alternative.

Also, you can consider taffy_cpp as an alternative to the well-known Yoga library (which is also written in C++, but supported by a big company and used in many projects in various languages).

Version

Current state of this library sources reflects the state of Taffy sources tree for:

• Commit: 47aa8d43f7f8004c59e9c6d06bab54bea60c915b
  • In tree: 47aa8d4

Configuring

Define	Description
TAFFY_FEATURE_BLOCK_LAYOUT	Enable Block layout algorithm support
TAFFY_FEATURE_FLEXBOX	Enable Flexbox layout algorithm support (and related Style properties)
TAFFY_FEATURE_GRID	Enable Grid layout algorithm support (and related Style properties)
TAFFY_FEATURE_TAFFY_TREE	Enable Taffy struct support
TAFFY_FEATURE_DEBUG	Enable layout algorithm execution-steps debug printing via DebugLogger
TAFFY_FEATURE_PROFILE	Enable some additional debug printing during layout algorithm execution
TAFFY_CONFIG_TEST	Enable extra printing in 'tests'
TAFFY_CONFIG_PANIC_UNWIND	(default) In case of panic - called assert(false) with stack unwinding
TAFFY_CONFIG_PANIC_ABORT	In case of panic - called std::abort() (causes SIGABRT signal throwing)

Dependencies

For third-party dependencies shipped with this library (and their versions), read third_party/README.md.

FAQ

• Question: Why it written in C++11 over modern C++17/C++20/etc ?

• Answer: First of all, in C++11, the minimum necessary things were introduced to make the C++ code look (and behave) like original Taffy Rust implementation: lambdas, (good) templates, scoped enumerations, constexpr functions, type traits, SFINAE, auto type deduction, move semantics, etc. That's why C++98 was not used :D

  Low requirements for C++ support in compilers means wider code 'applicability'. In our imperfect world, there is an incredible number of devices (with various architectures) under which you can compile C++ code, but vendor's compiler may supports only good old C++11 or C. I mean microelectronics or various outdated systems that cannot be easily updated.

  Once you find yourself in a situation where you need to do something useful in such harsh conditions, you will thank God that we still have useful libraries, written with old standard but can be used almost anywhere :)

  However, the code also has to be written under severe restrictions, without the features introduced in the new standards (like better constexpr rules introduced since C++17, or concepts from C++20), and with usage of third-party libraries that back-port needed functionality from next standards.

  Also, this does not mean that we are stuck on the 'old' C++11 standard - this library (due to C++ backwards compatibility, which also a great advantage) we can easily use in next or any future language versions. Any needed features of that versions may be enabled under conditional compile-time C++ version check (via #if pragma). This only means, that (for greater good) our code must be written in a such way, that allows us to be used anywhere, not in 'modern' environment (or which we consider to be).

  TL;DR: C++11 was chosen due to wider support over newer standard versions. You can check C++11 support in various compilers (and versions from which such support began) here.

• Question: Why this library written in 'header-only' manner?

• Answer: Let's take a look at some advantages and disadvantages (that I was able to quickly come up with) of header-only library distribution:

  • Advantages:

    • Header-only library easier to integrate, since user need to specify only include path in build system, instead of building library first as static or shared library, then use public headers & link over it.

    • Header-only library easier to configure, since user only need to add defines into build system, instead of building a library with special flags that will be included as defines in a special configuration file that will need to be included in every public header.

    • Header-only library is suitable for code that contains a lot of templates and constexpr functions (that this project abounds in).

    • Header-only library is easier to 'amalgamate' into a single header file, that also makes it much easier to distribute & integrate.

    • Header-only library provides for compiler all its sources, and during built it may easily throw out unused code, that cannot be removed from already built shared library.

  • Disadvantages:

    • We cannot easily specify special compilation flags when using header-only library, for example: build it with extra optimization due to high performance needs. In case of shared or static library, we can easily build it with -O3 or -ffast-math without changing build rules for rest of the user project code.

      • As workaround for it, header-only library may be build separately, with exposing API only via C interface. Also, it's suitable for FFI.

    • Header-only library slightly increases compilation time

    • In non-header-only library easier to resolve circular types dependencies, by moving dependent code into source files.

  TL;DR: I see a struggle here between two important properties:

  • Simple integration, configuration, distribution;
  • Simple compilation fine-tuning.

  Fine-tuning may be achieved by extra wrapping or in some other way, so I prefer header-only manner to achieve easier usage.

• Question: Why it named so taffy_cpp - not Taffy-cpp or even Taffy.cpp (like whisper.cpp)?

• Answer: For a some strange paranoid reason, I prefer 'safe' naming, that can be used in various contexts: in various file-systems with various naming rules, and also in source code in any language. That's why for naming here is avoided 'space', 'minus' or 'dot' symbols, or any non-ascii :D Also it makes us easy to search for such name.