android-go

README

android-go

The android-go project aims to provide a platform (namely an SDK) for writing native Android apps in Go programming language. All things here were designed to be less coupled as possible, thus maintaining a great level of flexibility while keeping things simple and easy to use. The approach and tools are different from gomobile, please distinguish them apart.

The project was one of the best Go Newsletter items of 2016. In this final issue of the year, they look back at the most popular Go news and links of 2016. 🌟

❗️Important! Please see cmd/android-project utility that replaces the original android from SDK that has been stripped in latest SDK releases. All example Makefiles were updated, I advise you to do the same rather than stick to old SDK versions.

Project structure

android

Package android provides Go bindings for the Android NDK API. They've been automatically generated by c-for-go using the official NDK headers from android-23 platform. Keep in mind that different NDK platforms may implement different sets of API available, thus some of features used by this binding may not be available in older versions of platform. But I tested with the android-21 toolchain and got no issues. Some files, like android/sensors.go for example, have been written by hand to expose some features that CGO does not handle well.

This package allows to write code that works directly with NDK API, bypassing all the CGO bookkeeping and boilerplate bloat in your code. But safety is strictly advised. There is also a JNI calling mechanism that allows easy interactions with Java VM and exposes the full potential of Android SDK! See android/jni_util.go for example of toggling Android keyboard and other JNI-based utils.

Example usages: app/queue.go, example, example-egl, nk-android.

cmd/android-project

Tool android-project is a simple replacement for infamous android util from Android SDK, prior to Android SDK Tools Revision 25.3.0 (March 2017) release when they dropped that util abruptly and got back a stripped version later. Needs to be installed first:

go get github.com/xlab/android-go/cmd/android-project

app

Package app implements a NativeActivity glue layer required to properly handle the startup process and the native activity events. Import this package into your Go application to make it Android-compatible. Some pieces required for a proper main.main trampoline have been borrowed from gomobile, the absolute minimum to get this stuff invokable as a native activity. Most of the code in this package provides wrappers around NativeActivity event callbacks.

Example usages: example, example-egl, nk-android.

egl

Package egl provides Go bindings for EGL API. They've been automatically generated by c-for-go using the official NDK headers from android-23 platform. All functions have their reference to the offical Khronos documentation. Some files, like egl/errors.go for example, have been written by hand to expose some features that would make it more idiomatic in the Go world.

Examples of usage in conjuction with the android package: example-egl, nk-android.

gles

Package gles provides Go bindings for the OpenGL ES v1 API. They've been automatically generated by c-for-go using the official NDK headers from android-23 platform. All functions have their reference to the offical documentation.

Example of usage in conjuction with the android package: example-egl.

gles2

Package gles2 provides Go bindings for the OpenGL ES v2 API. They've been automatically generated by c-for-go using the official NDK headers from android-23 platform. All functions have their reference to the offical documentation.

Example of usage in conjuction with the android package: nk-android.

gles3

Package gles3 provides Go bindings for the OpenGL ES v3 API. They've been automatically generated by c-for-go using the official NDK headers from android-23 platform. All functions have their reference to the offical documentation.

Example of usage in conjuction with the android package: nk-android.

gles31

Package gles31 provides Go bindings for the OpenGL ES v3.1 API. They've been automatically generated by c-for-go using the official NDK headers from android-23 platform. All functions have their reference to the offical documentation. The OpenGL ES computing API is supported.

Examples

Refer the example links to get more info about them.

There are three examples. The first example is a template app showing how to create and build an Android application using the absolute minimum of code and boilerplate. It also shows the primitives of an activity and how to handle activity events, there is no visual part, so be ready to read the lines from the ADB logcat. If this one works correctly on your device, my congratulations. If not, please open an issue.

The example-egl leverages all three packages together: android, egl and of course gles (OpenGL ES 1.0) to create an visual app that animates its color based on the accelerometer values. It also reads input events such as key events and multitouch motion events (with pressure, if supported by the device), you can check these events in the ADB logcat. Please see the video of the expected behaviour:

And recently I took nuklear package and implemented a few backends in Go, including two for Android that initialize OpenGL ES 2 or ES 3 context using android, egl, gles2 and gles3 packages. They also responsible for handling touch and other input events. So now it is possible to create GUI apps for Android, see nk-android for an example Nuklear GUI app.

Android keyboard toggling video.

On existing tools or why not just use Gomobile

TL;DR it's a "three wheel bicycle" in terms of hacking flexibility. Conversely, this project tries to fill the niche by providing a platform that is minimal as possible and respects the bleeding-edge features such as OpenGL ES 3.1, ES 3.2 and of course Vulkan API.

GoMobile has different aims and motivation with a lot of implications. First of all, it has been grown as a bootstrap-script. That's it: a tool with a lot of hardcoded logic that helped to popularize Go on mobile platforms. Still provides a simple way to start building Android and iOS apps in no time, without diving deeply into any of the platform-specific complications. It provides a lot of wrappers and helpers that abstract all the platform-related boilerplate and logic away, making your apps look the same on any platform: Android, iOS, PC (Linux/OS X/Windows).

Also, considering that binding feature of GoMobile, it's a good option to use when you already have lots of Java/Obj-C code and want to integrate some of Go libs into the project. The tool is mostly for experienced mobile developers who just want to try Go sometimes. They provide a framework that hides platform details, but they also may be to restrictive and limited due to this and can't be used for crazy experimenting stuff.

An example: for Android developent, gomobile defaults to r10 SDK with android-15 stripped-down NDK, there is a lot of code written to automate this process and there is no way to override this environment, even by rewriting a lot of gomobile bootstrapping code. It's a great mess. I wasted too much time trying to switch to the r12-beta1 SDK and the android-23 NDK platform. Instead of providing a good document how to build the Go-based apps and incorporate them into any of the existing development process, GoMobile project introduces tons of hardcoded scripts.

Contributing

Feel free to share bugs, I expect a lot of weird cases. Please also share this project in social networks so more people would know how to write Go apps for Android that are not limited.

License

All the code except when stated otherwise is licensed under the MIT license.