h3_dart 0.5.0

The package provides Dart version of the H3 Core library, a hexagon-based geographic grid system

H3 Dart & Flutter

H3 version: 3.7.2

The package allows to use H3 library directly in your Flutter or Dart application

The package uses C version under the hood. Works via FFI, bindings are automatically generated using ffigen

// Get hexagons in specified triangle.
final hexagons = h3.polyfill(
  resolution: 5,
  coordinates: [
    GeoCoord(20.4522, 54.7104),
    GeoCoord(37.6173, 55.7558),
    GeoCoord(39.7015, 47.2357),
  ],
);

Most of C's H3 functions are available in H3 class, which you can get using H3Factory. But if you can't find method you need, you can call C function directly, althrough it's more complicated, because you'll need to work directly with FFI (you will need to worry about allocation and native types). If you want to try, you can use H3CFactory to get access to H3C instance (import 'package:h3_flutter/internal.dart' or 'package:h3_dart/internal.dart').

The package also contains few methods ported from JS library Geojson2H3. To access them you should instantiate Geojson2H3 class using const Geojson2H3(h3).

Setup

Flutter

Add h3_flutter package to pubspec.yaml, import it and load:

import 'package:h3'

final h3 = const H3Factory().load();
final geojson2h3 = Geojson2H3(h3);

Dart

Add h3_dart package to pubspec.yaml.

Get compiled h3 library, depending on your platform it may have extension .so, .dll or any.

You can compile it using C-code placed in c folder in this repository. It has small changes comparing to original Uber's code to make it more compatible with iOS and macOS versions of h3_flutter. This code is recompiled and used for testing everytime tests are launched, so it should work well.

Otherwise, you can compile original Uber's code, which also should work well, just make sure you use correct version - https://github.com/uber/h3

Place your library somewhere and load it using H3Factory().byPath('path/to/library.dll'):

---

Tests

To make tests work you need to execute scripts/prepare_tests.sh script. The script builds h3 library from C code.
The script is designed for macOS and therefore it probably work only under this system.

How to update the package to use latest H3 version

~Good luck~

You need cmake tool, if you're on macos use next command to install it:

brew install cmake # install cmake

Clone h3 repository and create work folders:

git clone https://github.com/uber/h3 tmp/h3_sources 
# git checkout ... - checkout on commit you need, currently stable versions are in stable-3.x branch
mkdir tmp/h3_sources/build
cd tmp/h3_sources/build

Generate h3api.h file and copy it to c/h3lib folder:

cmake ..
rm -rf ../../../c/h3lib // recreate the folder to remove old h3 files
mkdir ../../../c/h3lib

cp src/h3lib/include/h3api.h ../../../c/h3lib

Copy other source files (*.h and *.c) to the folder.

cd ..
cp src/h3lib/include/* ../../c/h3lib
cp src/h3lib/lib/* ../../c/h3lib

Copy c/h3lib folder to ios and macos folders with scripts/sync_h3lib.sh script:

sh scripts/sync_h3lib.sh

You need to add .h and .c files to the project using XCode if you want to launch example (for iOS and macOS).
You can face some build errors, in my case i just followed xcode instructions to solve them.

Code generation tool called ffigen is used to create C-to-Dart bindings.
To run it, you need to install LLVM:

brew install llvm

If you're using M1 Mac, as of now, you need to install x86 version of LLVM, to do it you need to install x86 version of Homebrew.

All H3 public functions should be specified in ffigen.yaml file Run flutter pub run ffigen --config ffigen.yaml to generate bindings