- Qt 6.4
- Active Qt
- OpenGL Example (ActiveQt)
- Qt 6.4.3 Reference Documentation

# OpenGL Example (ActiveQt)

The OpenGL example demonstrates the use of the default factory and QAxFactory::isServer(), and the implementation of an additional COM interface using QAxBindable and QAxAggregated. The server executable can run both as an ActiveX server and as a stand-alone application.

The ActiveX control in this example uses the QGlWidget class in Qt to render an OpenGL scene in an ActiveX. The control exposes a few methods to change the scene.

The application uses QAxFactory through the `QAXFACTORY_BEGIN()`, `QAXCLASS()` and `QAXFACTORY_END()` macros to expose the `GLBox` widget as an ActiveX control.

     #include <QAxFactory>

     QAXFACTORY_BEGIN(
         "{2c3c183a-eeda-41a4-896e-3d9c12c3577d}", // type library ID
         "{83e16271-6480-45d5-aaf1-3f40b7661ae4}") // application ID
         QAXCLASS(GLBox)
     QAXFACTORY_END()

The implementation of `main` initializes the QApplication object, and uses `QAxFactory::isServer()` to determine whether or not it is appropriate to create and show the application interface.

     /*
       The main program is here.
     */

     int main(int argc, char *argv[])
     {
         QApplication a(argc,argv);

         if (QOpenGLContext::openGLModuleType() != QOpenGLContext::LibGL) {
             qWarning("This system does not support OpenGL. Exiting.");
             return -1;
         }

         if (!QAxFactory::isServer()) {
             GLObjectWindow w;
             w.resize(400, 350);
             w.show();
             return a.exec();
         }
         return a.exec();
     }

The `GLBox` class inherits from both the QOpenGLWidget class to be able to render OpenGL, and from QAxBindable.

     #include <QAxBindable>

     class GLBox : public QOpenGLWidget,
                   public QOpenGLFunctions_1_1,
                   public QAxBindable
     {
         Q_OBJECT
         Q_CLASSINFO("ClassID",     "{5fd9c22e-ed45-43fa-ba13-1530bb6b03e0}")
         Q_CLASSINFO("InterfaceID", "{33b051af-bb25-47cf-a390-5cfd2987d26a}")
         Q_CLASSINFO("EventsID",    "{8c996c29-eafa-46ac-a6f9-901951e765b5}")

The class reimplements the QAxBindable::createAggregate() function from QAxBindable to return the pointer to a QAxAggregated object.

     public:
     explicit GLBox(QWidget *parent, const char *name = nullptr);
     virtual ~GLBox();
     QAxAggregated *createAggregate() override;

     public slots:
     void                setXRotation(int degrees);

The implementation file of the `GLBox` class includes the `objsafe.h` system header, in which the `IObjectSafety` COM interface is defined.

     #include <objsafe.h>

A class `ObjectSafetyImpl` is declared using multiple inheritance to subclass the QAxAggregated class, and to implement the IObjectSafety interface.

     class ObjectSafetyImpl : public QAxAggregated,
                              public IObjectSafety
     {
     public:

The class declares a default constructor, and implements the queryInterface function to support the IObjectSafety interface.

         explicit ObjectSafetyImpl() = default;

         long queryInterface(const QUuid &iid, void **iface) override
         {
             *iface = nullptr;
             if (iid != IID_IObjectSafety)
                 return E_NOINTERFACE;

             *iface = static_cast<IObjectSafety*>(this);
             AddRef();
             return S_OK;
         }

Since every COM interface inherits `IUnknown` the `QAXAGG_IUNKNOWN` macro is used to provide the default implementation of the `IUnknown` interface. The macro is defined to delegate all calls to `QueryInterface`, `AddRef` and `Release` to the interface returned by the controllingUnknown() function.

         QAXAGG_IUNKNOWN;

The implementation of the `IObjectSafety` interface provides the caller with information about supported and enabled safety options, and returns `S_OK` for all calls to indicate that the ActiveX control is safe.

         HRESULT WINAPI GetInterfaceSafetyOptions(REFIID riid, DWORD *pdwSupportedOptions, DWORD *pdwEnabledOptions) override
         {
             Q_UNUSED(riid);
             *pdwSupportedOptions = INTERFACESAFE_FOR_UNTRUSTED_DATA | INTERFACESAFE_FOR_UNTRUSTED_CALLER;
             *pdwEnabledOptions = INTERFACESAFE_FOR_UNTRUSTED_DATA | INTERFACESAFE_FOR_UNTRUSTED_CALLER;
             return S_OK;
         }

         HRESULT WINAPI SetInterfaceSafetyOptions(REFIID riid, DWORD pdwSupportedOptions, DWORD pdwEnabledOptions) override
         {
             Q_UNUSED(riid);
             Q_UNUSED(pdwSupportedOptions);
             Q_UNUSED(pdwEnabledOptions);
             return S_OK;
         }
     };

The implementation of the `createAggregate()` function just returns a new `ObjectSafetyImpl` object.

     QAxAggregated *GLBox::createAggregate()
     {
         return new ObjectSafetyImpl();
     }

To build the example you must first build the QAxServer library. Then run `qmake` and your make tool in `examples/activeqt/wrapper`.

The demonstration requires your WebBrowser to support ActiveX controls, and scripting to be enabled.

In contrast to the other QAxServer examples Internet Explorer will not open a dialog box to ask the user whether or not the scripting of the GLBox control should be allowed (the exact browser behaviour depends on the security settings in the Internet Options dialog).

     <SCRIPT LANGUAGE="JavaScript">
     function setRot( form )
     {
         GLBox.setXRotation( form.XEdit.value );
         GLBox.setYRotation( form.YEdit.value );
         GLBox.setZRotation( form.ZEdit.value );
     }
     </SCRIPT>

     <p />
     An OpenGL scene:<br />
     <object ID="GLBox" CLASSID="CLSID:5fd9c22e-ed45-43fa-ba13-1530bb6b03e0"
     CODEBASE="http://qt.nokia.com/demos/openglax.cab">
     [Object not available! Did you forget to build and register the server?]
     </object><br />

     <form>
     Rotate the scene:<br />
     X:<input type="edit" ID="XEdit" value="0" /><br />
     Y:<input type="edit" name="YEdit" value="0" /><br />
     Z:<input type="edit" name="ZEdit" value="0" /><br />
     <input type="button" value="Set" onClick="setRot(this.form)" />
     </form>

Example project @ code.qt.io