roswasm_suite

Libraries for compiling C++ ROS nodes to Webassembly using Emscripten. Allows you to write C++ ROS nodes similar to how you would otherwise, and to then have them run in a webbrowser and communicate with ROS through rosbridge_websocket.

Dependencies

• Emscripten tested with version 1.39.10 but latest should do
• rosbridge_suite after the commit adding cbor-raw compression, latest develop should do:

  git clone https://github.com/RobotWebTools/rosbridge_suite -b develop # in workspace src folder

Building

catkin build is recommended, since catkin_make might leak configurations to other packages. Make sure to source the Emscripten environment before building the package:

source /path/to/emsdk/emsdk_env.sh
catkin build

Packages

• roscpp_json_serialize - library that serializes ROS messages to and from json
• roswasm - contains the roswasm client library and configures cmake to build dependent packages using Emscripten. It supports publishers, subscribers, service clients and timers
• roswasm_tutorials - contains examples corresponding to talker, listener and timers of roscpp
• roswasm_webgui - a proof of concept implementation of a ROS GUI library based on roswasm and imgui

Writing a roswasm node

The roswasm client library presents an API similar to roscpp, with the main differences being that most interfaces are heap allocated, and that Emscripten manages the event loop. Below is a shortened version of the corresponding listener example implementation.

#include <emscripten.h>
#include <roswasm/roswasm.h>
#include <std_msgs/String.h>

roswasm::NodeHandle* n;
roswasm::Subscriber* sub;

void chatterCallback(const std_msgs::String& msg)
{
    printf("I heard: [%s]\n", msg.data.c_str());
}

void loop() {}

extern "C" int main(int argc, char** argv)
{
    n = new roswasm::NodeHandle();
    sub = n->subscribe<std_msgs::String>("chatter", chatterCallback);
    emscripten_set_main_loop(loop, 10, 1);
    return 0;
}

For more complete examples, see the roswasm_tutorials package.

Building a roswasm package

The roswasm library uses catkin to build an emscripten project. All you have to do in your package that is using roswasm is to add it as a dependency in your cmake file and link against ${roswasm_LIBRARIES}. It will automatically set the Emscripten em++ compiler as the default for building and linking nodes. Note that you have to install and source the emscripten SDK before building your workspace. The following minimal cmake file includes a guard to check that Emscripten is present.

cmake_minimum_required(VERSION 2.8.3)
project(listener)

find_package(catkin REQUIRED COMPONENTS roscpp roswasm std_msgs)
catkin_package()

if (DEFINED ENV{EMSDK})

include_directories(${catkin_INCLUDE_DIRS})
add_executable(listener src/listener.cpp)
set_target_properties(listener PROPERTIES OUTPUT_NAME "listener.js")
target_link_libraries(listener ${roswasm_LIBRARIES})
configure_file(www/listener.html ${CATKIN_DEVEL_PREFIX}/${CATKIN_PACKAGE_BIN_DESTINATION}/listener.html COPYONLY)

endif()

Running an Emscripten node

Run node separately

Before starting any of the roswasm nodes, you need to have one instance of rosbridge_websocket running:

roslaunch rosbridge_server rosbridge_websocket.launch

After building your node, you can run it similar to the following command:

rosrun roswasm run.py _pkg:=roswasm_tutorials _node:=listener.html _display_port:=8080

This will start a webserver and allow you to view the page at localhost:8080. If you want to see the output from the node, open the browser debug console.

Combined launch file (alternative)

There is a also a convenience launch file to run both rosbridge_websocket as well as your roswasm node at the same time:

roslaunch roswasm run_server.launch pkg:=roswasm_tutorials node:=listener.html