libdart_openmvg

OpenMVG bindings for dart.

OpenMVG is an AI graphics application that supports feature detection and surface-from-motion capabilities

Getting Started

This project is a starting point for a Flutter FFI plugin, a specialized package that includes native code directly invoked with Dart FFI.

Building dependencies.

My current project structure is as follows:

+- main_project
  +- libdart_openmvg (this project)
  +- libffmpeg
  +- cwalk (git clone https://github.com/likle/cwalk.git)
  +- openMVG (git clone https://github.com/openMVG/openMVG.git)

The install prefix for openMVG is expected to be openMVG/build/_install. I'll fix this at some point, but I hard-coded it to get the project built.

To build libdart_openmvg...

$ mkdir build && cd build
$ cmake -DCMAKE_INSTALL_PREFIX=_install ../src

The C/C++ Bindings

To run cunit tests...

$ cd build
$ ./test_image

Or to auto-build & run cunit tests...

$ # in the libdart_openmvg project root
$ ./scripts/watch_compilelib.sh # in one terminal
$ ./scripts/watch_test.sh # in another terminal

Ensure you have the entr command installed.

Now anytime you save a .c/.cxx/.h/CMakeLists.txt file, the program will be recompiled and retested.

The Dart Tests

To run the dart tests ensure that the C bindings are built.

$ dart --define=CURRENT_EXEC_DIR="${ROOT_DIR}" test ${TEST_DIR}

Or if you want to rerun the tests every time the C or dart files are changed:

$ ./scripts/watch_darttest.sh

Project structure

This template uses the following structure:

• src: Contains the native source code, and a CmakeFile.txt file for building that source code into a dynamic library.

• lib: Contains the Dart code that defines the API of the plugin, and which calls into the native code using dart:ffi.

• platform folders (android, ios, windows, etc.): Contains the build files for building and bundling the native code library with the platform application.

Building and bundling native code

The pubspec.yaml specifies FFI plugins as follows:

  plugin:
    platforms:
      some_platform:
        ffiPlugin: true

This configuration invokes the native build for the various target platforms and bundles the binaries in Flutter applications using these FFI plugins.

This can be combined with dartPluginClass, such as when FFI is used for the implementation of one platform in a federated plugin:

  plugin:
    implements: some_other_plugin
    platforms:
      some_platform:
        dartPluginClass: SomeClass
        ffiPlugin: true

A plugin can have both FFI and method channels:

  plugin:
    platforms:
      some_platform:
        pluginClass: SomeName
        ffiPlugin: true

The native build systems that are invoked by FFI (and method channel) plugins are:

• For Android: Gradle, which invokes the Android NDK for native builds.
  • See the documentation in android/build.gradle.
• For iOS and MacOS: Xcode, via CocoaPods.
  • See the documentation in ios/archimedes_mobile_lib.podspec.
  • See the documentation in macos/archimedes_mobile_lib.podspec.
• For Linux and Windows: CMake.
  • See the documentation in linux/CMakeLists.txt.
  • See the documentation in windows/CMakeLists.txt.

Binding to native code

To use the native code, bindings in Dart are needed. To avoid writing these by hand, they are generated from the header file (src/archimedes_mobile_lib.h) by package:ffigen. Regenerate the bindings by running flutter pub run ffigen --config ffigen.yaml.

Invoking native code

Very short-running native functions can be directly invoked from any isolate. For example, see sum in lib/archimedes_mobile_lib.dart.

Longer-running functions should be invoked on a helper isolate to avoid dropping frames in Flutter applications. For example, see sumAsync in lib/archimedes_mobile_lib.dart.

Flutter help

For help getting started with Flutter, view our online documentation, which offers tutorials, samples, guidance on mobile development, and a full API reference.

Developer Notes

You'll get an error with Eiger, so watch out.

$ make
finition.hpp:17:10: fatal error: Eigen/Dense: No such file or directory
   17 | #include <Eigen/Dense>
      |          ^~~~~~~~~~~~~
compilation terminated.

$ sudo at install -y libeigen3-dev
$ sudo ln -sf /usr/include/eigen3/Eigen /usr/include/Eigen

git clone --single-branch --branch n6.1 https://git.ffmpeg.org/ffmpeg.git

Can I expose FILE in dart?

Yea...no! https://github.com/dart-lang/sdk/issues/4160

Instead, I'll have to load the data in directly.

buliding open mvg needs to be done with the PIC flag

$ cmake ../src -DCMAKE_INSTALL_PREFIX="../../openMVG/build/_install" -DCMAKE_POSITION_INDEPENDENT_CODE=ON

A good SFM example (that I'm basically ripping from) can be found here:

./openMVG/src/software/SfM/main_SfM.cpp