8.8.10. Plugin class - Basic information

All plugins, especially hardware-related ones (derived from AddInActuator, AddInDataIO, …), have some similar or identical base components. These are described in this chapter. Therefore it is recommended to read this chapter before continuing with the specific documentation about the type of plugin you want to create. The information given in this chapter is mainly important for plugins finally derived from classes AddInActuator (actuator-plugins) or AddInDataIO (displays, cameras, AD-converter, …). Algorithm or filter-plugins behave a little bit different, however it remains worth to read this document first. Common components for actuator and dataIO plugins

The following components and structures are equal for all plugins of type actuator or dataIO (including grabbers):

  1. Every plugin has an internal set of parameters, that can can be read or changed by the method getParam and setParam (class AddInBase).

  2. These parameters are saved in the map m_params, member of class AddInBase.

  3. Each parameter is an instance of class ito::Param.

  4. The plugin itself is responsible if the new input to any parameter is valid or if the parameter is readonly as has to reject wrong input. For this purpose the parameters’ meta information or flags can be used.

  5. Every plugin executes its methods mainly in an own thread.

  6. The communcation between the plugin and its GUI-components (Config-Dialog, Dock-Widget in main window) must therefore be done using a signal-slot-connection or a simple invoke, that allows to call methods in another thread.

  7. The plugin’s init method is called with the mandatory and optional parameters, those default is set the in the plugin’s interface and which are updated by the user input.

The basic scheme of the live-cycle of any plugin is depicted in the following figure:


At startup of itom, one single instance (singleton) of each plugin interface class is created and managed by the AddInManager. Later, an instance of the real plugin can be requested, for instance in a python-script or by a C-function call. The arguments to this request are two vectors of mandatory and optional parameters (instances of class ParamBase), that are passed to the initialization of the plugin. The default state of these vectors is obtained by the corresponding interface class (vectors m_initParamsMand and m_initParamsOpt). These default values have or can be replaced by the values, e.g. indicated in the python script (this is automatically done by itom).

Then AddInManager calls getAddInInst() of the plugin interface, that is creating a new instance of the plugin by calling its constructor. Please consider, that the mandatory and optional parameters are not passed to the constructor yet. Then, the pointer to the plugin is passed back to the AddInManager, that now moves the plugin to a newly created thread. From that point on, methods of the plugin should only be called using a thread-communcation technique, provided by Qt, e.g. using the method invokeMethod or the signal-slot-system of Qt. Then the method init of the plugin is “invoked” by the AddInManager and the mandatory and optional initialization parameters are passed as arguments.

Next, the plugin can be used. Whenever a method of the plugin is called, either by python or any C-method, this call has to be executed again by an “over-thread” communcation technique (invokeMethod or signal-slot). The last argument of such a call always is a locked instance of ItomSharedSemaphore. The caller then waits until the semaphore will be released in the plugin’s method or a timeout occurred. Please make sure, that you release the semaphore in your plugin’s method only at the point, when you don’t need any parameters given by the caller any more. Usually it is released at the bottom of your method. Only in special cases (like method waitForDone (for actuators) it makes sense to release it earlier. For more information about the semaphore see ItomSharedSemaphore.

Finally, if the plugin should be closed, the inverse function calls with respect to the initialization are executed. That means, the AddInManager is at first invoking the method call of the plugin (still in its own thread). Then the plugin is moved back to the main thread and then AddInManager forces the deletion of the plugin by the method closeThisInst of the corresponding interface class.


In some cases, it is not possible to initialize the hardware (some cameras) in another thread than the main thread. Since this initialization should be done in the init method of the plugin, itom provides a possibility to call init before moving the plugin to the new thread. Hence, those both steps in this scheme are switched. This can be done by setting the member m_callInitInNewThread of the plugin interface class from its default value true to false. However, only use this possibility if there is no other chance, since the GUI is completely blocked during an initialization executed in the main thread (see also Plugin interface class). Plugin-Framework

The bare framework of any plugin-class of type DataIO, Actuator, … (but not Algo), looks like this:

 1#include "common/addInInterface.h"
 3class MyPlugin : public ito::AddInActuator OR public ito::AddInDataIO OR public ito::AddInGrabber
 5    Q_OBJECT
 7    public:
 8        friend class MyPluginInterface;
10    protected:
11        ~MyPlugin(){};
12        MyPlugin();
14    public slots:
15        ito::RetVal init(QVector<ito::ParamBase> *paramsMand, QVector<ito::ParamBase> *paramsOpt, ItomSharedSemaphore *waitCond = NULL);
16        ito::RetVal close(ItomSharedSemaphore *waitCond);
18        ito::RetVal getParam(QSharedPointer<ito::Param> val, ItomSharedSemaphore *waitCond = NULL);
19        ito::RetVal setParam(QSharedPointer<ito::ParamBase> val, ItomSharedSemaphore *waitCond = NULL);
21        ito::RetVal execFunc(const QString funcName, QSharedPointer<QVector<ito::ParamBase> > paramsMand, ...
22            ... QSharedPointer<QVector<ito::ParamBase> > paramsOpt, QSharedPointer<QVector<ito::ParamBase> > paramsOut, ...
23            ... ItomSharedSemaphore *waitCond = NULL);
25    private slots:
26        void dockWidgetVisibilityChanged(bool visible);

In the corresponding source file you need to write two defines before including the header file above:

4#include "myPluginHeaderFromAbove.h"
6//implement your code here

In this chapter, hints about implementing the methods in the definitions above are given. In the detailed chapters about every type of plugin, these class definitions will then be extended by the type-specific methods.

At first, your plugin class must be derived from class ito::AddInActuator if you want to create an actuator plugin, from class ito::AddInGrabber if you want to create a camera or grabber plugin and finally class ito::AddInDataIO for other hardware-related plugins. All those classes are derived from AddInBase. Next, the plugin’s class must have the macro Q_OBJECT defined, such that the plugin is able to participate at the signal-slot-system of Qt. That is necessary for a multi-thread-communcation with the plugin.

The constructor and destructor of the plugin are defined in the protected section. Only the interface class is able to call these methods, since the interface class is declared as friend of the plugin in line 6.

Then, there are five methods in the public slots section, which should be overwritten from their base definition in the class AddInBase. The methods init and close are important for the startup and shutdown of an instance of the plugin. getParam and setParam provide read and/or write access to parameters of the plugin, that are usually stored in the member-map m_params (however you can also use getParam and setParam to read and write other parameters. In some special cases, it is necessary to add further, arbitrary functions to the plugin, for instance in order to start an extra calibration process. These calls are executed by the general method execFunc, those first argument is the name of the function. You only have to implement this function, if you need this feature. Until now, this has only been necessary for a low amount of plugins.

Before the details about the implementation for these methods are explained, let us also take a look at the definition of the class AddInBase itself. Only few public or protected member functions of this class must be overwritten by the plugin (those, that have been described above). However, there are still a lot of further member methods which can be overwritten or useful for the functionality of your plugin. The description of the accessible member functions and attributes (public, protected, signals, public slots) is described in AddInBase.

Now, let us give some hints about the implementation of the methods, that have to be overwritten: Constructor

The constructor is a protected member method and should usually only be called by the corresponding interface class. A exemplary implementation is:

 1MyPlugin::MyPlugin(... further parameters ...) :
 2    AddInActuator()
 4    //create internal parameter map
 5    ito::Param paramVal("name", ito::ParamBase::String | ito::ParamBase::Readonly, "MyPluginName", NULL);
 6    m_params.insert(paramVal.getName(), paramVal);
 7    //... add further parameters to map
 9    //now create dock widget for this plugin (if available)
10    MyPluginDockWidget *myDockWidget = new MyPluginDockWidget(this);
12    //here: connect signals from the dock widget to the plugin
13    // connections that inform the dock widget about changes in parameters, status... should be created
14    // and destroyed in the method 'dockWidgetVisibilityChanged'.
16    //if you can and want, you can assign the unique identification string for this plugin here:
17    //m_identifier = QString("my unique plugin nr: %1").arg(yourSerialNumber)
18    //you can also set this in the init-method.
20    Qt::DockWidgetAreas areas = Qt::LeftDockWidgetArea | Qt::RightDockWidgetArea;
21    QDockWidget::DockWidgetFeatures features = QDockWidget::DockWidgetClosable | QDockWidget::DockWidgetFloatable | QDockWidget::DockWidgetMovable;
22    createDockWidget("MyDockWidgetName", features, areas, myDockWidget);

For the constructor consider the following remarks:

  1. The constructor is executed in the main thread and therefore is able to create widgets like the dock widget.

  2. The constructor can have an arbitrary amount and type of parameters; the method getAddInInst of the interface class must be adapted to them.

  3. Call the constructor of the base class (e.g. AddInActuator, AddInDataIO, AddInGrabber) in your constructor.

  4. The constructor does not get the mandatory and optional parameters given by to user for initializing the plugin.

  5. Create all internal parameters that are part of the parameter-map m_params and provide some default values.

  6. If your plugin should provide a dock widget (that can be shown as dockable toolbox in the main window of itom), follow the snippet from the example above.

  7. If your dock widget should be visible at initialization of the plugin or should be undocked as default state, overwrite and change the method dockWidgetDefaultStyle of class AddInBase.

  8. See the specific documentation of each plugin to see which internal parameters must be available and which conventions exist for some specific parameters, that can be created.

  9. If you want, set the unique identification string m_identifier in this constructor. You can also set it later in the init-method. If you don’t set it, the auto-assigned unique ID is used for identifying your instance. Destructor

Use the destructor (executed in main thread) for some final deletion work. Usually an empty body of the destructor is sufficient.

MyPlugin::~MyPlugin() {} Init

The method init has the following bare framework:

 1ito::RetVal MyPlugin::init(QVector<ito::ParamBase> *paramsMand, QVector<ito::ParamBase> *paramsOpt, ItomSharedSemaphore *waitCond)
 3    ItomSharedSemaphoreLocker locker(waitCond);
 4    ito::RetVal retValue;
 6    //use the content of paramsMand and paramsOpt (order and type
 7    // with respect to m_initParamsMand and m_initParamsOpt of
 8    // interface class) in order to initialize the hardware and
 9    // change values of the m_params-map if necessary.
11    //if you want you can set the unique identification string here:
12    //m_identifier = QString("IAmAUniqueStringDescribingThisPlugin")
14    // emit signal about changed parameters
15    emit parametersChanged(m_params);
17    //release the wait condition and set its returnValue before
18    if (waitCond)
19    {
20        waitCond->returnValue = retValue;
21        waitCond->release();
22    }
24    setInitialized(true); //plugin is initialized
25    return retValue;

Consider the following hints for the implementation of the init-method:

  1. Usually it is executed in a new thread (see here)

  2. The parameters are the filled mandatory and optional parameter vectors, those default implementation has been given in the constructor of the interface class.

  3. You can be sure, that both the order and type of those plugins remains invariant.

  4. Initialize the plugin with respect to these parameters.

  5. If necessary change the value of the internal parameters m_params.

  6. If so, emit the signal parametersChanged(m_params).

  7. At the end of the method release the wait condition.

  8. Afterwards call setInitialized(true) in order to confirm the initialization of the plugin.

  9. See the specific documentation of each plugin to see, what else has to be done in the method init. Close

The method close is always executed as last method in the plugin thread. Disconnect your hardware in this method. A simple exemplary implementation is:

 1ito::RetVal MyPlugin::close(ItomSharedSemaphore *waitCond)
 3    ItomSharedSemaphoreLocker locker(waitCond);
 4    ito::RetVal retValue;
 6    //your code comes here
 8    if (waitCond)
 9    {
10        waitCond->release();
11        waitCond->returnValue = retValue;
12    }
13    return retValue;
14} getParam

This method is the getter-method for reading the current value of internal parameters, that usually are an item of the map m_params. In this method (like in others, too) methods provided by the itom API are used. Therefore, you need to include the API header in your source file, e.g. by

#include "common/apiFunctionsInc.h"

The prototype for the method getParam then looks like this:

 1ito::RetVal MyPlugin::getParam(QSharedPointer<ito::Param> val, ItomSharedSemaphore *waitCond)
 3    ItomSharedSemaphoreLocker locker(waitCond);
 4    ito::RetVal retValue;
 5    QString key;
 6    bool hasIndex = false;
 7    int index;
 8    QString suffix;
 9    ParamMapIterator it;
11    //parse the given parameter-name (if you support indexed or suffix-based parameters)
12    retValue += apiParseParamName(val->getName(), key, hasIndex, index, suffix);
14    if (retValue == ito::retOk)
15    {
16        //gets the parameter key from m_params map (read-only is allowed, since we only want to get the value).
17        retValue += apiGetParamFromMapByKey(m_params, key, it, false);
18    }
20    if (!retValue.containsError())
21    {
22        //put your switch-case.. for getting the right value here
24        //finally, save the desired value in the argument val (this is a shared pointer!)
25        //if the requested parameter name has an index, e.g. roi[0], then the sub-value of the
26        //array is split and returned using the api-function apiGetParam
27        if (hasIndex)
28        {
29            *val = apiGetParam(*it, hasIndex, index, retValue);
30        }
31        else
32        {
33            *val = *it;
34        }
35    }
37    if (waitCond)
38    {
39        waitCond->returnValue = retValue;
40        waitCond->release();
41    }
43    return retValue;

The getParam is either called directly, by changing the thread or by the Python script execution, if the appropriate method getParam in Python is called. For guaranteeing a thread-safe implementation, the first argument is a shared pointer to a value of class ito::Param. In case of success, the requested value must be saved into this given parameter. The second argument is a string containing the parameter name.

It is possible to pass a single parameter name or to follow a given string-syntax in order to also give a certain array index as well as an additional suffix string. Rules for this syntax are given in the section Possible parameter names for parameter-map m_params. In order to split the given raw name into its possible components name, index and suffix, the method parseParamName defined in helperCommon.h can be used. In the exemplary implementation above, the parameter-name is finally searched in the map m_params and if found, the value of this parameter is copied to the given argument val. However, this implementation is the most basic one and you can also implement further lines of code.

Since this method can also be called from another thread, an instance of ItomSharedSemaphore is passed, that finally needs to be released. The destruction of the pointer waitCond is done by the locker-instance locker. setParam

The method getParam is the analog method to setParam. However, in setParam you will not only passed a parametername but also the new value for this parameter. Then you need to implement the following checks:

  • Check whether your internal parameter is read-only and if so, reject the set-command.

  • Verify the compatibility of the parameter-type of the new and internal parameter.

  • Consider further restrictions given by a possible meta information that is appended to the internal parameter and check if the new value fits to these restrictions.

  • If any internal parameter changed, emit the signal parametersChanged with m_params as argument. This signal is globally defined in the base class AddInBase and is for instance connected with GUI-elements like the possible dock-widget (toolbox) of this plugin.

Finally, an exemplary (simplified) version for the method setParam is:

 1ito::RetVal MyPlugin::setParam(QSharedPointer<ito::ParamBase> val, ItomSharedSemaphore *waitCond)
 3    ItomSharedSemaphoreLocker locker(waitCond);
 4    ito::RetVal retValue(ito::retOk);
 5    QString key;
 6    bool hasIndex;
 7    int index;
 8    QString suffix;
 9    ParamMapIterator it;
11    //parse the given parameter-name (if you support indexed or suffix-based parameters)
12    retValue += apiParseParamName( val->getName(), key, hasIndex, index, suffix );
14    if (isMotorMoving()) //this if-case is for actuators only.
15    {
16        retValue += ito::RetVal(ito::retError, 0, tr("any axis is moving. Parameters cannot be set").toLatin1().data());
17    }
19    if (!retValue.containsError())
20    {
21        //gets the parameter key from m_params map (read-only is not allowed and leads to ito::retError).
22        retValue += apiGetParamFromMapByKey(m_params, key, it, true);
23    }
25    if (!retValue.containsError())
26    {
27        //OPTION 1:
28        //here the new parameter is checked whether its type corresponds or can be cast into the
29        // value in m_params and whether the new type fits to the requirements of any possible
30        // meta structure.
31        retValue += apiValidateParam(*it, *val, false, true);
33        //OPTION 2 (recommended):
34        //if you program for itom 1.4.0 or higher (Interface version >= 1.3.1) you should use this
35        //API method instead of the one above: The difference is, that incoming parameters that are
36        //compatible but do not have the same type than the corresponding m_params value are cast
37        //to the type of the internal parameter and incoming double values are rounded to the
38        //next value (depending on a possible step size, if different than 0.0)
39        retValue += apiValidateAndCastParam(*it, *val, false, true, true);
40    }
42    if (!retValue.containsError())
43    {
44        if (key == "async")
45        {
46            //check the new value and if ok, assign it to the internal parameter
47            retValue += it->copyValueFrom( &(*val) );
48        }
49        else if (key == "demoKey")
50        {
51            //check the new value and if ok, assign it to the internal parameter
52            retValue += it->copyValueFrom( &(*val) );
53        }
54        else
55        {
56            //all parameters that don't need further checks can simply be assigned
57            //to the value in m_params (the rest is already checked above)
58            retValue += it->copyValueFrom( &(*val) );
59        }
60    }
62    if (!retValue.containsError())
63    {
64        emit parametersChanged(m_params); //send changed parameters to any connected dialogs or dock-widgets
65    }
67    if (waitCond)
68    {
69        waitCond->returnValue = retValue;
70        waitCond->release();
71    }
73    return retValue;

In this base implementation, the parametername is firstly searched in the m_params-map. If found, the internal parameter is checked for the read-onlyness. Next, the method distinguishes between numeric and non-numeric parameters, since the numeric-ones can possibly be casted from one numeric type to another one. If these pre-requisites are met, you should then check the new value for certain restrictions and if this is met, too, the internal parameter can be filled with the content of the given, new value. Else, appropriate error messages should be returned and the semaphore waitCond must finally be released.

If you want to set multiple parameters in an uninterrupted sequence, you can also call or invoke the method setParamVector defined in AddInBase. You don’t have to implement this method, since this is already done. For more infos about this method, see the definition of AddInBase (AddInBase). Extend your plugin by registering further functions

As already mentioned above, you can extend the set of methods of each plugin, defined by their base classes, by registering further functions. This is for instance useful, if you want to provide methods for starting a gamma correction, starting a specific calibration, …

Each such method has the same arguments than the init-method of the plugin:

  • A vector of mandatory parameters (class ParamBase)

  • A vector of optional parameters (class ParamBase)

  • A Vector of out-only parameters (class ParamBase)

In the constructor of your plugin, you need to register each of those methods by also predefining the default set of all parameter-vectors (mandatory, optional, out). Only, if this step has been done, the corresponding method can be called, for instance by using the method exec in the Python scripting language. The call to this method finally leads to a call of the method execFunc, defined in the class AddInBase, which has to be overwritten in your plugin, if you want to provide at least one additional method.

The first parameter of execFunc is the name of the additional method. Therefore you need to check for this name and then execute the corresponding algorithm.

An exemplary implementation of the method execFunc is

 1ito::RetVal MyPlugin::execFunc(const QString funcName, QSharedPointer<QVector<ito::ParamBase> > paramsMand, ...
 2    ...QSharedPointer<QVector<ito::ParamBase> > paramsOpt, QSharedPointer<QVector<ito::ParamBase> > paramsOut, ItomSharedSemaphore *waitCond)
 4    ito::RetVal retValue = ito::retOk;
 5    ito::ParamBase *param1 = NULL;
 6    ito::ParamBase *param2 = NULL;
 8    if (funcName == "saveXMLParams")
 9    {
10        param1 = ito::getParamByName(&(*paramsMand), "filename", &retValue);
11        param2 = ito::getParamByName(&(*paramsOpt), "overwriteIfExists", &retValue);
13        if (!retValue.containsError())
14        {
15            retValue += XmlParameter::saveXmlParams( param1->getVal<char*>(), m_xmlParams, static_cast<bool>(param2->getVal<int>()));
16        }
17    }
18    else
19    {
20        retValue += ito::RetVal::format(ito::retError,0,tr("function name '%s' does not exist").toLatin1().data(), funcName.toLatin1().data());
21    }
23    if (waitCond)
24    {
25        waitCond->returnValue = retValue;
26        waitCond->release();
27        waitCond->deleteSemaphore();
28        waitCond = NULL;
29    }
31    return retValue;

In this method, one additional function (name saveXMLParams) is integrated, which only is called with one mandatory and optional parameter and no further output parameter. The corresponding registration of this method is integrated in the constructor of your plugin:

1//register exec functions
2QVector<ito::Param> pMand;
3pMand << ito::Param("filename", ito::ParamBase::String | ito::ParamBase::In, NULL, tr("absolute filename to xml-parameter file").toLatin1().data());
4QVector<ito::Param> pOpt;
5pOpt << ito::Param("overwriteIfExists", ito::ParamBase::Int | ito::ParamBase::In, 0, 1, 1, tr("parameter description").toLatin1().data());
6QVector<ito::Param> pOut;
7registerExecFunc("saveXMLParams", pMand, pOpt, pOut, tr("description"));

Please consider that only the following parameter types are allowed as output parameters. It is therefore not allowed to use dataObjects as output parameters. In this case, pass a dataObject as optional or mandatory parameter and mark their type with the flags ito::ParamBase::In combined with ito::ParamBase::Out (by-reference):

  • String

  • Char

  • Integer

  • Double

  • Char-Array

  • Integer-Array

  • Double-Array Possible parameter names for parameter-map m_params

The parameters which you add to the m_params map, must have a name which fits to the following rules:

  • The name starts with a lower or upper case character, hence a value between a-z or A-Z

  • The first character of the name can be followed by an infinite number of alpha-numerical characters (including characters like _ or -).

If the user tries to get or set a parameter e.g. using the python-commands setParam or getParam, the parameter name firstly is checked if it exists in the m_params vector before the corresponding getter or setter methods in the plugin are called. However not the full given parameter string has to match any available key-name in the m_params map, since there are further information which can be encoded in the parameter name:

Sometimes it is useful to create a parameter as integer or double array, e.g. for the speed values of every single axis. In this case you will create a parameter with the name speed having a type typeDoubleArray. Then the user can either access the whole array using the real parameter name speed, or the user can access one single value of the array by appending the index within brackets at the parameter name. In this case, it is the programmers task to parse the given parameter string and separate the parameter’s real name (here: speed) and the index. Then the index has to be checked with respect to its lower and upper bound.

As further possibility, it is also allowed to append further information to a parameter. This is done by appending a colon-character to the parameter name followed by any string, which is the additional information string.

To sum this description up, let us assume that the parameter in m_params has the name PARAMNAME, which fits to the rules above. Then itom will accept parameter names, which correspond to the following rules:





INDEX has to be any fixed-pointer number, the ADDITIONALTAG can be any string.

It is the programmer’s responsibility to split the given parameter name in the three components PARAMNAME, INDEX and ADDITIONALTAG if the corresponding parameter has the ability to handle indexed-values or even additional information (encoded in ADDITIONALTAG).

In order to execute this split you can use the api-method

ito::RetVal apiParseParamName(const QString &name, QString &paramName, bool &hasIndex, int &index, QString &additionalTag)

defined in apiFunctionsInc.h.

As an alternative you can use the following regular expression:

 1QString regularExpression = "^([a-zA-Z]+\\w*)(\\[(\\d+)\\]){0,1}(:(.*)){0,1}$";
 2QRegExp rx(regularExpression)
 3if (rx.indexIn(yourString) == -1)
 5    //yourString does not match the regular expression
 9    QStringList components = rx.capturedTexts();
10    //components consists of the following sub-strings:
11    /*
12    [0] full string
13    [1] PARAMNAME
14    [2] [INDEX] or empty-string if no index is given
15    [3] INDEX or empty-string if no index is given
16    [4] :ADDITIONALTAG or empty-string if no tag is given
17    [5] ADDITIONALTAG or empty-string if no tag is given
18    */