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https://github.com/twistedfall/opencv-rust

Rust bindings for OpenCV 3 & 4
https://github.com/twistedfall/opencv-rust

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Rust bindings for OpenCV 3 & 4

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README 

        
# Rust OpenCV bindings



[![Build status](https://github.com/twistedfall/opencv-rust/workflows/opencv-rust/badge.svg)](https://github.com/twistedfall/opencv-rust/actions/workflows/opencv-rust.yml)

[![Documentation](https://docs.rs/opencv/badge.svg)](https://docs.rs/opencv)

[![Package](https://img.shields.io/crates/v/opencv.svg)](https://crates.io/crates/opencv)



Experimental Rust bindings for OpenCV 3 and 4.



The API is usable, but unstable and not very battle-tested; use at your own risk.



[Changelog](https://github.com/twistedfall/opencv-rust/blob/master/CHANGES.md)

[Troubleshooting](https://github.com/twistedfall/opencv-rust/blob/master/TROUBLESHOOTING.md)

[Support the project](https://github.com/sponsors/twistedfall)



## Quickstart



Make sure the supported OpenCV version (3.4 or 4.x) and Clang (part of LLVM, needed for automatic binding

generation) are installed in your system.



Update your Cargo.toml

```toml

opencv = "0.88.8"

```



Import prelude

```rust

use opencv::prelude::*;

```



## Getting OpenCV



See [INSTALL.md](https://github.com/twistedfall/opencv-rust/blob/master/INSTALL.md) for instructions on how to install required

system dependencies.



## Troubleshooting



See [TROUBLESHOOTING.md](https://github.com/twistedfall/opencv-rust/blob/master/TROUBLESHOOTING.md) for some common issues and

their solutions.



## Environment variables



The following variables must be set when building without `pkg_config`, `cmake` or `vcpkg`. You can set them

on any platform, the specified values will override those automatically discovered.



* `OPENCV_LINK_LIBS`

  Comma separated list of library names to link to. `.lib`, `.so` or `.dylib` extension is optional. If you

  specify the ".framework" extension then build script will link a macOS framework instead of plain shared

  library.

  E.g. "opencv_world411".



  If this list starts with '+' (plus sign) then the specified items will be appended to whatever the system

  probe returned. E.g. a value of "+dc1394" will do a system discovery of the OpenCV library and its linked

  libraries and then will additionally link `dc1394` library at the end. Can be useful if the system probe

  produces a mostly working setup, but has incomplete link list, or the order is wrong (especially important

  during static linking).



* `OPENCV_LINK_PATHS`

  Comma separated list of paths to search for libraries to link. E.g. "C:\tools\opencv\build\x64\vc15\lib".

  The path list can start with '+', see `OPENCV_LINK_LIBS` for a detailed explanation (e.g.

  "+/usr/local/lib").



* `OPENCV_INCLUDE_PATHS`

  Comma separated list of paths to search for system include files during compilation. E.g.

  "C:\tools\opencv\build\include". One of the directories specified therein must contain

  "opencv2/core/version.hpp" or "core/version.hpp" file, it's used to detect the version of the headers.

  The path list can start with '+', see `OPENCV_LINK_LIBS` for a detailed explanation (e.g.

  "+/opt/cuda/targets/x86_64-linux/include/").



The following variables are rarely used, but you might need them under some circumstances:



* `OPENCV_PACKAGE_NAME`

  In some cases you might want to override the pkg-config, cmake or vcpkg package name, you can use this

  environment variable for that. If you set it pkg-config will expect to find the file with that name and `.pc`

  extension in the package directory. Cmake will look for that file with `.cmake` extension. And vcpkg will use

  that name to try to find package in `packages` directory under `VCPKG_ROOT`. You can also use separate

  environment variables to set different package names for different package systems:

    * `OPENCV_PKGCONFIG_NAME`

    * `OPENCV_CMAKE_NAME`

    * `OPENCV_VCPKG_NAME`



* `OPENCV_CMAKE_BIN`

  Path to cmake binary (used in OpenCV discovery process using cmake). If not set then just "cmake" will be

  used. For example, you can set something like "/usr/local/bin/cmake" here.



* `OPENCV_DISABLE_PROBES`

  Comma separated list of OpenCV package auto-discovery systems to exclude from running. Might be useful if

  one of the higher priority systems is producing incorrect results. Can contain the following values:

    * environment - reads data only from the `OPENCV_LINK_LIBS`, `OPENCV_LINK_PATHS` and `OPENCV_INCLUDE_PATHS`

      environment variables

    * pkg_config

    * cmake

    * vcpkg_cmake - like vcpkg, but only uses vcpkg for path discovery, the actual OpenCV probe is done using

      cmake (cmake related environment variables are applicable with this probe)

    * vcpkg



* `OPENCV_MSVC_CRT`

  Allows selecting the CRT library when building with MSVC for Windows. Allowed values are `"static"` for `/MT`

  and `"dynamic"` for `/MD`.



The following variables affect the building the of the `opencv` crate, but belong to external components:



* `PKG_CONFIG_PATH`

  Where to look for `*.pc` files see the [man pkg-config](https://linux.die.net/man/1/pkg-config)

  Path specified here must contain `opencv.pc` (pre OpenCV 4) or `opencv4.pc` (OpenCV 4 and later).



* `VCPKG_ROOT`, `VCPKGRS_DYNAMIC` and `VCPKGRS_TRIPLET`

  The root of `vcpkg` installation, flag allowing use of `*.dll` libraries and selected `vcpkg` triplet, see the

  [documentation for `vcpkg` crate](https://docs.rs/vcpkg)



* `OpenCV_DIR`

  The directory that contains OpenCV package cmake files. Usually there are `OpenCVConfig.cmake`,

  `OpenCVConfig-version.cmake` and `OpenCVModules.cmake` in it.



* `LD_LIBRARY_PATH`

  On Linux it sets the list of directories to look for the installed `*.so` files during runtime.

  [Linux documentation](https://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html) has more info.

  Path specified here must contain `libopencv_*.so` files.



* `DYLD_LIBRARY_PATH` and `DYLD_FALLBACK_LIBRARY_PATH`

  Similar to `LD_LIBRARY_PATH`, but for loading `*.dylib` files on macOS, see [man dyld](https://man.cx/dyld(1))

  and [this SO answer](https://stackoverflow.com/a/3172515) for more info. Path specified here must contain

  `*.dylib` files.



* `PATH`

  Windows searches for `*.dll`s in `PATH` among other places, be sure to set it up, or copy required OpenCV

  `*.dll`s next to your binary. Be sure to specify paths in UNIX style (/C/Program Files/Dir) because colon

   in `PATH` might be interpreted as the entry separator. Summary [here](https://stackoverflow.com/a/6546427).



* clang crate environment variables

  See crate's [README](https://github.com/KyleMayes/clang-sys/blob/master/README.md#environment-variables)



## Cargo features

* There is a feature named after each OpenCV module (e.g. `imgproc`, `highgui`, etc.). They are all enabled by

  default, but if a corresponding module is not found then it will silently be ignored. If you need to select a

  specific set of modules be sure to disable the default features and provide the required feature set:

  ```

  opencv = { version = ..., default-features = false, features = ["calib3d", "features2d", "flann"]}

  ```

* `rgb` - allow using [`rgb`](https://crates.io/crates/rgb) crate types as `Mat` elements



## API details



[API Documentation](https://docs.rs/opencv) is automatically translated from OpenCV's doxygen docs. Most

likely you'll still want to refer to the official [OpenCV C++ documentation](https://docs.opencv.org/master)

as well.



### OpenCV version support



The following OpenCV versions are supported at the moment:

* 3.4

* 4.x



### Minimum rustc version (MSRV)



Currently, Rust version 1.66.0 or later is required. General policy is that rust version from 1 year ago is supported.

Bumping versions older than that is not considered a breaking change.



### Platform support



Currently, the main development and testing of the crate is performed on Linux, but other major platforms are

also supported: macOS and Windows.



For some more details please refer to the CI build scripts:

[Linux OpenCV install](https://github.com/twistedfall/opencv-rust/blob/master/ci/install-ubuntu.sh),

[macOS OpenCV install as framework](https://github.com/twistedfall/opencv-rust/blob/master/ci/install-macos-framework.sh),

[macOS OpenCV install via brew](https://github.com/twistedfall/opencv-rust/blob/master/ci/install-macos-brew.sh),

[Windows OpenCV install via Chocolatey](https://github.com/twistedfall/opencv-rust/blob/master/ci/install-windows-chocolatey.sh),

[Windows OpenCV install via vcpkg](https://github.com/twistedfall/opencv-rust/blob/master/ci/install-windows-vcpkg.sh),

[Test runner script](https://github.com/twistedfall/opencv-rust/blob/master/ci/script.sh).



### Functionality



Generally the crate tries to only wrap OpenCV API and provide some convenience functions

to be able to use it in Rust easier. We try to avoid adding any functionality besides

that.



### Errors



Most functions return a `Result` to expose a potential C++ exception. Although some methods like property reads

or functions that are marked CV_NOEXCEPT in the OpenCV headers are infallible and return a naked value.



### CV_MAKETYPE



`CV_MAKETYPE` and related `CV_MAT_DEPTH` constant functions are available to replace the corresponding OpenCV macros.

Yet it's usually easier to call `::opencv_type()` function on the corresponding Rust type. E.g.:

```rust

let t = u16::opencv_type(); // equivalent to CV_MAKETYPE(CV_16U, 1)

let t = Vec2f::opencv_type(); // equivalent to CV_MAKETYPE(CV_32F, 2)

```



### C++ operators

Some C++ operators are supported, they are converted to the corresponding functions on Rust side. Here is the

list with the corresponding function name:

* `[]` → `get()` or `get_mut()`

* `+`, `-` → `add()`, `sub()`

* `*`, `/` → `mul()`, `div()`

* `()` (function call) → `apply()`

* `=` → `set()`

* `*` (deref) → `try_deref()` or `try_deref_mut()`

* `==`, `!=` → `equals()`, `not_equals()`

* `>`, `>=` → `greater_than()`, `greater_than_or_equal()`

* `<`, `<=` → `less_than()`, `less_than_or_equal()`

* `++`, `--` → `incr()`, `decr()`

* `&`, `|`, `^` → `and()`, `or()`, `xor()`

* `!` → `negate()`



### Class fields



Fields of OpenCV classes are accessible through setters and getters. Those functions are infallible, they

return the value directly instead of `Result`.



### Infallible functions



For infallible functions (like setters) that accept `&str` values the following logic applies: if a Rust

string passed as argument contains null byte then this string will be truncated up to that null byte. So if

for example you pass "123\0456" to the setter, the property will be set to "123".



### Callbacks



Some API functions accept callbacks, e.g. `set_mouse_callback`. While currently it's possible to successfully

use those functions there are some limitations to keep in mind. Current implementation of callback handling

leaks the passed callback argument. That means that the closure used as a callback will never be freed during

the lifetime of a program and moreover Drop will not be called for it. There is a plan to implement possibility

to be able to free at least some closures.



### Unsafety



Although the crate tries to provide an ergonomic Rust interface for OpenCV, don't expect

Rust safety guarantees at this stage. It's especially true for the borrow-checking and the

shared mutable ownership. Notable example would be `Mat` which is a reference counted

object in its essence. You can own a seemingly separate `Mat` in Rust terms, but

it's going to be a mutable reference to the other `Mat` under the hood. Treat safety

of the crate's API as you would treat one of C++, use `clone()` when needed.



## Contrib modules



To be able to use some modules you need to have [`opencv_contrib`](https://github.com/opencv/opencv_contrib)

installed. You can find the full list of contrib modules [here](https://github.com/opencv/opencv_contrib/tree/master/modules).



## Missing modules and functions



While most of the API is covered, for various reasons (that might no longer hold) there are modules and

functions that are not yet implemented. If a missing module/function is near and dear to you, please file an

issue (or better, open a pull request!).



## The binding strategy



This crate works similar to the model of python and java's OpenCV wrappers - it uses libclang to parse the

OpenCV C++ headers, generates a C interface to the C++ API, and wraps the C interface in Rust.



All the major modules in the C++ API are merged together in a huge `cv::` namespace. We instead made one rust

module for each major OpenCV module. So, for example, C++ `cv::Mat` is `opencv::core::Mat` in this crate.



The methods and field names have been snake_cased. Methods arguments with default value lose these default

values, but they are reported in the API documentation.



Overloaded methods have been mostly manually given different names or automatically renamed to *_1, *_2, etc.



## Older OpenCV branches support

### OpenCV 2



If you can't use OpenCV 3.x or higher, the (no longer maintained) `0.2.4` version of this crate is known to

work with OpenCV `2.4.7.13` (and probably other 2.4 versions). Please refer to the README.md file for that

version because the crate has gone through the considerable rewrite since.



### OpenCV 3.2



The last version with confirmed OpenCV 3.2 support is 0.75.0, after that this branch of OpenCV is no longer

tested and supported. It may still work though.



## Contributor's Guide



The binding generator code lives in a separate crate under [binding-generator](binding-generator). During the

build phase it creates bindings from the header files and puts them into [bindings](bindings) directory. Those

are then transferred to [src](src) for the consumption by the crate users.



The crate itself, as imported by users, consists of generated rust code in [src](src) committed to the repo.

This way, users don't have to handle the code generation overhead in their builds. When developing this crate,

you can test changes to the binding generation using `cargo build -vv`. When changing the `binding-generator`,

be sure to push changes to the generated code!



If you're looking for things to improve be sure to search for `todo` and `fixme` labels in the project

source, those usually carry the comment of what exactly needs to be fixed.



The license for the original work is [MIT](https://opensource.org/licenses/MIT).



Special thanks to [ttacon](https://github.com/ttacon) for yielding the crate name.