rpi-ws281x-java

rpi281x wrapper for Java using SWIG

TL;DR

Successfully tested on a RaspberryPi 3B+

1. set RaspberryPi ssh username and password in gradle.properties
2. run ./gradlew installSwigOnPi
3. run ./gradlew buildNativeOnPi
4. run ./gradlew publishToMavenLocal -PtargetComp=11
5. run ./gradlew runExample -PtargetComp=11 -PamountOfLeds=16 -Pexample=RainbowExample to test.
   set -PamountOfLeds to the amount of LEDs on the strip.
   set -Pexample to the name of the example-class (in src/examples) you want to execute.
   set -PtargetComp=11 if the java version on your raspi is 11 (often true because it's the default-jdk). Otherwise it is assumed that the java version on your raspi matches the one gradle uses. Only 11 can be passed currently.
6. kill runing example java app by ssh-ing into your raspi and using htop to send a SIGINT signal to the process.

To build on a raspberry pi

Run src/scripts/createNativeLib.sh to generate the SWIG java code and generate the libws2811.so native library (For a tutorial on how to install SWIG, see "Install SWIG on RaspberryPi" below).

Run ./gradlew assemble to compile the java code and create a jar containing the compile class files and the native .so file.

To build from another machine

Set the appropriate username, host and password (or path to private key) in gradle.properties.

Then, run ./gradlew buildNativeOnPi. Note that your RaspberryPi needs to have ssh installed as gradle will use its ssh client.

Alternatively, you can also use the script build-native-on-remote-pi.sh with bash or a bash-compatible shell (like babun, cygwin, or git-bash on windows.).

This will copy the project to the pi, and run the script in the previous section, and copy the .so library back to the dev machine. After that, run .\gradlew assemble to compile the java code and create a jar containing the compile class files and the native .so file. The easiest way to use the jar would be to publish it to a maven repository, or your local .m2 repository using ./gradlew publishToMavenLocal and use maven coordinates in your maven or gradle project.

To install SWIG on the RaspberryPi

You can try ./gradlew installSwigOnPi to automatically execute all the steps detailed below on your pi.

NOTE: The default-jdk-headless which this task will try to install works only on pis with ARMv7+ architecture (check with the command cat /proc/cpuinfo). The script will try to detect this and install the zulu jdk as an alternative, but this has only been tested on a raspberrypi Zero so far. On my RasPi Zero this task took 30min the majority of which was spent building SWIG. On the RasPi 3 B it took 8 mins.

You can read more in the pi4j docs.

These commands worked for me:

1. Install prereqs

sudo apt-get install build-essential libpcre2-dev libpcre3-dev

2. Install default jdk

sudo apt install default-jdk-headless

3. Download swig tarball and unzip

wget http://prdownloads.sourceforge.net/swig/swig-4.1.1.tar.gz
tar -xzvf swig-4.1.1.tar.gz

4. Enter directory and start building

cd swig-4.1.1
./configure && make

5. Execute an example as a check

cd Examples/java/class && make check

6. Install SWIG

cd ../../../
sudo make install
swig -version

SWIG Version 4.1.1

Compiled with g++ [x86_64-pc-linux-gnu]

Configured options: +pcre

Please see https://www.swig.org for reporting bugs and further information

For reference, the SWIG DOCS.

Attribution

• SWIG generation and native lib compiling based on scripts at https://github.com/limpygnome/build-tv
• build-native-on-remote-pi script based on script at https://github.com/Cacodaimon/rpi_ws281x4j
• Loading JNI native .so file code based on code at https://github.com/mattjlewis/diozero/blob/master/diozero-ws281x-java