In YARP, a "plugin" is an implementation of some service for which there are many choices and alternatives.
In YARP, a "plugin" is an implementation of some service for which there are many choices and alternatives.
There are two basic types of plugin for YARP: devices and carriers. Devices implement interfaces to cameras, controlboards, and other hardware. Carriers implement different network protocols. Users select which devices and carriers they want to have included in YARP (or they can compile them separately).
Optional devices and carriers are enabled or disabled via CMake options. Enabling a device or carrier may require extra libraries to be installed.
Before discussing how to add new devices or carriers into the YARP library itself, we look at how a user can make their own library of plugins. This is a useful first step in getting confident about how plugins work.
Making a single plugin
Let's take the FakeFrameGrabber example device developed in Getting Started with YARP Devices and turn it into a plugin. Make a directory called "fake_grabber" (or whatever you like), and add the following as "fake_grabber/FakeFrameGrabber.h".
private:
int w, h;
public:
h = w = 0;
}
bool open(
int w,
int h) {
this->w = w;
this->h = h;
return w>0 && h>0;
}
return open(desiredWidth,desiredHeight);
}
return true;
}
return h;
}
virtual int width()
const {
return w;
}
};
fakeFrameGrabber: A fake camera for testing.
int width() const override
Return the width of each frame.
int height() const override
Return the height of each frame.
FakeFrameGrabber()=default
bool open(yarp::os::Searchable &config) override
Configure with a set of options.
bool getImage(yarp::sig::ImageOf< yarp::sig::PixelRgb > &image) override
Get an image from the frame grabber.
bool close() override
Close the DeviceDriver.
Interface implemented by all device drivers.
A base class for nested structures that can be searched.
virtual bool check(const std::string &key) const =0
Check if there exists a property of the given name.
A single value (typically within a Bottle).
And add this as "fake_grabber/FakeFrameGrabber.cpp":
private:
int w, h;
public:
h = w = 0;
}
bool open(
int w,
int h) {
this->w = w;
this->h = h;
return w>0 && h>0;
}
return open(desiredWidth,desiredHeight);
}
return true;
}
return h;
}
virtual int width()
const {
return w;
}
};
Here's a quick test program for the device, call it "fake_grabber/test_fake_grabber.cpp":
#include <stdio.h>
int main(
int argc,
char *argv[]) {
if (!dd.isValid()) {
printf(
"fake_grabber not available\n");
return 1;
}
printf(
"*** Device failed to supply images\n");
return 1;
}
printf(
"*** Device can supply images\n");
} else {
printf(
"Failed to read an image\n");
return 1;
}
return 0;
}
A factory for creating driver objects of a particular type.
A base class for factories that create driver objects.
A container for a device driver.
A mini-server for performing network communication in the background.
size_t width() const
Gets width of image in pixels.
size_t height() const
Gets height of image in pixels.
For streams capable of holding different kinds of content, check what they actually have.
An interface to the operating system, including Port based communication.
int main(int argc, char *argv[])
YARP plugins need a CMakeLists.txt that says how to build them. The CMakeLists.txt is written in the following style (this would be "fake_grabber/CMakeLists.txt"):
# SPDX-FileCopyrightText: 2006-2021 Istituto Italiano di Tecnologia (IIT)
# SPDX-FileCopyrightText: 2006-2010 RobotCub Consortium
# SPDX-License-Identifier: BSD-3-Clause
cmake_minimum_required(VERSION 3.16)
find_package(YARP COMPONENTS os dev REQUIRED)
# Declare a device called "fake_grabber", with C++ type
# "FakeFrameGrabber" defined in FakeFrameGrabber.h. This code sets
# up a CMake option for selecting the device, and prepares
# some initialization boilerplate code if needed.
# If the device is not selected, "SKIP_foo" will be defined.
yarp_prepare_plugin(fake_grabber
CATEGORY device
EXTRA_CONFIG WRAPPER=frameGrabber_nws_yarp
)
if(NOT SKIP_fake_grabber)
yarp_add_plugin(fake_grabber)
target_sources(fake_grabber
PRIVATE
)
target_link_libraries(fake_grabber
PRIVATE
${YARP_LIBRARIES}
)
option(COMPILE_TEST "Compile fake grabber test")
if(COMPILE_TEST)
add_executable(test_fake_grabber)
target_sources(test_fake_grabber
PRIVATE
test_fake_grabber.cpp
)
target_link_libraries(test_fake_grabber PRIVATE ${YARP_LIBRARIES})
endif()
endif()
This style is used so that individual plugin directories can be compiled standalone for testing purposes, but will also work when bundled into a larger library. If we configure and compile this directory, we get a test program that we can run straight away. If it works, then we could immediately plug this device into YARP.
Making a plugin library
Here we put together a library of YARP plugins from scratch.
First, let's start with a stub test program, "userlib/test_userlib.cpp":
#include <stdio.h>
int main(
int argc,
char *argv[]) {
printf("Test program stub\n");
return 0;
}
Here's a CMakeLists.txt ("userlib/CMakeLists.txt") to compile this:
cmake_minimum_required(VERSION 3.16)
find_package(YARP COMPONENTS os REQUIRED)
add_executable(test_userlib)
target_sources(test_userlib PRIVATE test_userlib.cpp)
target_link_libraries(test_userlib PRIVATE YARP::YARP_os
YARP::YARP_init)
Now, let's prepare a plugin library. We need to include YarpPlugin in order to get some helper functions for this. We'll just have one plugin for now, the fake_grabber device. Here's the modified "userlib/CMakeLists.txt" file:
# SPDX-FileCopyrightText: 2006-2021 Istituto Italiano di Tecnologia (IIT)
# SPDX-FileCopyrightText: 2006-2010 RobotCub Consortium
# SPDX-License-Identifier: BSD-3-Clause
cmake_minimum_required(VERSION 3.16)
find_package(YARP COMPONENTS os dev REQUIRED)
yarp_begin_plugin_library(userlib)
add_subdirectory(fake_grabber)
yarp_end_plugin_library(userlib)
add_executable(test_userlib)
target_sources(test_userlib PRIVATE test_userlib.cpp)
target_link_libraries(test_userlib PRIVATE ${YARP_LIBRARIES})
target_link_libraries(test_userlib PRIVATE userlib)
This assumes that we have moved "fake_grabber" into the "userlib" directory.
Now, let's update our test program, "userlib/test_userlib.cpp":
#include <stdio.h>
int main(
int argc,
char *argv[]) {
if (!dd.isValid()) {
printf(
"fake_grabber not available\n");
return 1;
}
printf(
"Was able to instantiate a fake_grabber\n");
return 0;
}
#define YARP_DECLARE_PLUGINS(name)
#define YARP_REGISTER_PLUGINS(name)
Utilities for manipulating the YARP network, including initialization and shutdown.
The main, catch-all namespace for YARP.
We can now use cmake to configure and build, either in the "userlib" directory, or in the "userlib/fake_grabber" directory. These files are available in the YARP source package, under the directory "example/plugins".
Adding a plugin into YARP
In directory ${YARP_ROOT}/src/devices/CMakeLists.txt, there is a list of device directories. We could just add another line to insert fake_grabber. There is no requirement that the fake_grabber subdirectory be in any particular location. Similarly, carriers can be added in $YARP_ROOT/src/carriers/CMakeLists.txt.