Create an RViz dockable panel w/ catkin and Qt5

Question

Hi everyone,

These past days, I'm trying to write an RViz dockable panel following the tutorial here.
My goal is basically to display – for now – an empty panel (the strict minimum, for a beginning).
The problem is that all the tutorial is writing with both rosbuild and Qt4, while I would like to use catkin and Qt5. Each time I'm trying to compile, I keep having this error message :

[ERROR] [1426085794.672184440]: PluginlibFactory: The plugin for class 'plugin_panel/Hi' failed to load.  Error: Failed to load library /home/mdufour/catkin_ws_test/devel/lib/libplugin_panel.so. Make sure that you are calling the PLUGINLIB_EXPORT_CLASS macro in the library code, and that names are consistent between this macro and your XML. Error string: Could not load library (Poco exception = /home/mdufour/catkin_ws_test/devel/lib/libplugin_panel.so: undefined symbol: _ZTVN8my_panel11PluginPanelE)

My package directory looks like this :

plugin_panel/
|__ CMakeLists.txt
|__ package.xml
|__ plugin_description.xml
|__ src/
    |__ plugin_panel.cpp

All the code is in the .cpp file, for simplification.
Here's my CMakeLists.txt :

cmake_minimum_required(VERSION 2.8.11)

project(plugin_panel)

find_package(Qt4 REQUIRED)
find_package(catkin REQUIRED)

include(${QT_USE_FILE})
add_definitions(${QT_DEFINITIONS})

add_library(${PROJECT_NAME} src/plugin_panel.cpp)

target_link_libraries(${PROJECT_NAME} ${QT_LIBRARIES} ${catkin_LIBRARIES})

This is my .cpp (very basic!) :

#include <QWidget>
#include <QHBoxLayout>
#include <QLabel>

#include <rviz/panel.h>

namespace my_panel
{
    class PluginPanel: public rviz::Panel
    {
        Q_OBJECT

    public:
        PluginPanel(QWidget* parent = 0):
            rviz::Panel(parent)
            {
                QHBoxLayout* topic_layout = new QHBoxLayout;
                topic_layout->addWidget(new QLabel("Hi!"));
            }
    };
}

#include <pluginlib/class_list_macros.h>
PLUGINLIB_EXPORT_CLASS(my_panel::PluginPanel, rviz::Panel)

The package.xml (overloaded for sure) :

<?xml version="1.0"?>
<package>
    <name>plugin_panel</name>

    <version>0.0.0</version>

    <description>
        An additional (yet empty) panel in RViz.
    </description>

    <maintainer email="[email protected]">Matthieu</maintainer>

    <license>BSD</license>

    <buildtool_depend>catkin</buildtool_depend>

    <build_depend>roscpp</build_depend>
    <build_depend>roslib</build_depend>
    <build_depend>rviz</build_depend>
    <build_depend>pluginlib</build_depend>
    <build_depend>class_loader</build_depend>

    <run_depend>roscpp</run_depend>
    <run_depend>roslib</run_depend>
    <run_depend>rviz</run_depend>
    <run_depend>pluginlib</run_depend>
    <run_depend>class_loader</run_depend>

    <export>
        <rviz plugin="${prefix}/plugin_description.xml"/>
    </export>
<package>

And finally the plugin_description.xml :

<library path="lib/libplugin_panel">
    <class name="plugin_panel/Hi"
           type="my_panel::PluginPanel"
           base_class_type="rviz::Panel">
        <description>
            An empty panel.
        </description>
    </class>
</library>

Phew! Sorry, that was heavy… I'm certainly missing something in one of those files, but I can't figure out what.

Thanks for your answers.

---

Originally posted by anonymous21729 on ROS Answers with karma: 15 on 2015-03-11

Post score: 0

Answer 1

target_link_libraries(${PROJECT_NAME} Qt5::Widgets ${catkin_LIBRARIES})

I'm not too familiar with Qt5, but I'm not sure whether Qt5::Widgets is an actual library name under Linux.

according to Using CMake with Qt 5 - Building Qt 5 projects with CMake, linking to Qt5 libraries with CMake should be done as follows (for the QtWidgets component):

target_link_libraries(YOUR_TARGET [..] ${Qt5Widgets_LIBRARIES})

That page has a lot of information on using CMake with Qt5 actually.

Also: according to Developing with Qt - The Transition from Qt 4.x to Qt 5, Qt5 could make use of C++11 features. Afaik, ROS (still) doesn't support that, and binary compatibility may not be guaranteed when mixing and matching (non)C++11 compatible object files/libraries.

---

Edit3:

find_package(catkin REQUIRED)

Shouldn't at least rviz be listed as COMPONENTS here?

Looking at the CMakeLists.txt of the catkinized version of the plugin tutorial package you linked to it would seem that you are missing some important parts:

find_package(catkin REQUIRED COMPONENTS rviz)
catkin_package()
include_directories(${catkin_INCLUDE_DIRS})
link_directories(${catkin_LIBRARY_DIRS})

## This plugin includes Qt widgets, so we must include Qt like so:
find_package(Qt4 COMPONENTS QtCore QtGui REQUIRED)
include(${QT_USE_FILE})

## I prefer the Qt signals and slots to avoid defining "emit", "slots",
## etc because they can conflict with boost signals, so define QT_NO_KEYWORDS here.
add_definitions(-DQT_NO_KEYWORDS)

## Here we specify which header files need to be run through "moc",
## Qt's meta-object compiler.
qt4_wrap_cpp(MOC_FILES
  src/drive_widget.h
  src/imu_display.h
  src/plant_flag_tool.h
  src/teleop_panel.h
)

## Here we specify the list of source files, including the output of
## the previous command which is stored in ``${MOC_FILES}``.
set(SOURCE_FILES
  src/drive_widget.cpp
  src/imu_display.cpp
  src/imu_visual.cpp
  src/plant_flag_tool.cpp
  src/teleop_panel.cpp 
  ${MOC_FILES}
)

## An rviz plugin is just a shared library, so here we declare the
## library to be called ``${PROJECT_NAME}`` (which is
## "rviz_plugin_tutorials", or whatever your version of this project
## is called) and specify the list of source files we collected above
## in ``${SOURCE_FILES}``.
add_library(${PROJECT_NAME} ${SOURCE_FILES})

target_link_libraries(${PROJECT_NAME} ${QT_LIBRARIES} ${catkin_LIBRARIES})

---

Originally posted by gvdhoorn with karma: 86574 on 2015-03-11

This answer was ACCEPTED on the original site

Post score: 1

---

Original comments

Comment by anonymous21729 on 2015-03-11:
Thanks for replying!

Unfortunately, I just re-wrote my CMakeLists.txt to follow the standards of Qt4 (using find_package(Qt4 REQUIRED) etc), and I still have the error message :(

Comment by gvdhoorn on 2015-03-11:
Ok, well, could you update your question then (CMakeLists.txt, etc)? Perhaps there is some other issue going on here.

Comment by gvdhoorn on 2015-03-11:
Please don't use answers as comments, use comments for that (this is not a traditional top-down forum).

You say "nothing happened at all": which bits did you copy, and what didn't happen?

Comment by Simon Schmeisser on 2015-08-17:
"I'm not too familiar with Qt5, but I'm not sure whether Qt5::Widgets is an actual library name under Linux." It's called a target generator or something like that and is the recommended way now (since CMake 2.8.11/12), it will add includes, libs, flags, .. http://doc.qt.io/qt-5/cmake-manual.html

Answer 2

I just stumbled across this error as well (while porting rviz to qt5) and will note the answer here for documentation purposes.

So the error you got from pluginloader tells you that your plugin shared object (.so) is not linked to everything it expects. This is because moc, the Meta Object Compiler is used by Qt to create some meta information about what classes, functions, signals, slots exist. moc reads header files searching for classes with the Q_OBJECT macro (short version ;) ). It then outputs a new cpp code file containing this information. This file has to be compiled and linked into your plugin.

The traditional way is what gvdhoorn wrote, the more modern way would be to add

set(CMAKE_AUTOMOC ON)
set(CMAKE_INCLUDE_CURRENT_DIR ON)

and you are done (works for qt4 and qt5).

If some errors remain, it might be because automoc is not perfect. It then helps to just add the header file to the sources list

Writing rviz plugins in Qt5 and loading them in a rviz that was compiled with Qt4 does not work. Neither does the other way around. But the code should be almost the same, so you can just recompile once rviz got ported to qt5

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Originally posted by Simon Schmeisser with karma: 229 on 2015-08-17

This answer was NOT ACCEPTED on the original site

Post score: 3

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Original comments

Comment by Huibuh on 2016-07-11:
Your comment "If some errors remain, it might be because automoc is not perfect. It then helps to just add the header file to the sources list" saved my day. After battling with this error for hours, this finally worked. Cheers!

Comment by chwimmer on 2017-01-17:
That saved my day too... Thank you so much for that comment.