Maybe Important - 2015-07-31 16:05 UTC-0800 Pritpal Bedi (bedipritpal at hotmail.com)(r417)[ HbQtQmlParts ]

[Pritpal Bedi]

2015-07-31 16:05 UTC-0800 Pritpal Bedi (bedipritpal at hotmail.com)(r417)

  + hbqtqmlparts

  + hbqtqmlparts/resources

  + hbqtqmlparts/resources/png

  + hbqtqmlparts/resources/png/left-32.png

  + hbqtqmlparts/resources/png/refresh-32.png

  + hbqtqmlparts/resources/png/right-32.png

  + hbqtqmlparts/resources/png/stop-32.png

  + hbqtqmlparts/resources/qml

  + hbqtqmlparts/resources/qml/BarcodeReader.qml

  + hbqtqmlparts/resources/qml/WebView.qml

  + hbqtqmlparts/resources/wav

  + hbqtqmlparts/resources/wav/barcode-beep.wav

  + hbqtqmlparts/resources/wav/camera-flash.wav

  + hbqtqmlparts/misc.prg

  + hbqtqmlparts/qmlbridge.prg

  + hbqtqmlparts/barcodereader.prg

  + hbqtqmlparts/webview.prg

  + hbqtqmlparts/hbqtqmlparts.hbc

  + hbqtqmlparts/hbqtqmlparts.hbp

  + hbqtqmlparts/hbqtqmlparts.hbx

  + hbqtqmlparts/hbqtqmlparts.qrc

  + hbqtqmlparts/tests

  + hbqtqmlparts/tests/demobarcodereader.prg

  + hbqtqmlparts/tests/demowebview.prg

  + hbqtqmlparts/tests/hbmk.hbm

  + qtcontribs.hbp

    + Added: hbqtqmlparts/hbqtqmlparts.hbp

    Initial commit of Harbour engine for QML manipulation.

    QML is the next-generation offering by Qt which facilitates to develop 

    modern-looking, javaScript based applications. QML is also the core 

    language adopted by Ubuntu mobile plaforms and its concept of 

    one-os-fit-all-devices shift. So seems QML is set to become the 

    protocol of choice for so many applications.

    Harbour's implementation of Qt, i.e. HbQt, is essentially a widget 

    based implementation. It took me a while to turn to QML because 

    of the necessity to have barcode reading inside my mobile offerings.

    I remained reluctant to give QML a try for a long time because of the 

    complexity how Signal/Slot mechanism is implemented in Harbour.

    But when I took initiative, I found that it is simpler than my fear.

    Bottom line is : we can start using QML to some extent alsong-with 

    and within our existing widget based apps.

    CLASS HbQtQmlBridge() provides the building blocks to stream-line 

    the complexity of signal/slots, set/get properties, execute methods, etc.

    

       CLASS HbQtQmlBridge()

       METHOD init( oParent )

       METHOD create( oParent )

       METHOD setQml( cQml )                                -> lSuccess

       METHOD show()                                        -> NIL

       METHOD setProperty( cProperty, xValue )              -> lSuccess

       METHOD setChildProperty( cChild, cProperty, xValue ) -> lSuccess

       METHOD getProperty( cProperty )                      -> oQVariant | NIL

       METHOD getChildProperty( cChild, cProperty )         -> oQVariant | NIL

       METHOD invokeMethod( cMethod, ... )                  -> oQVariant | NIL

       METHOD connect( cSignal, bBlock )                    -> lSuccess

       METHOD connectChild( cChild, cSignal, bBlock )       -> lSuccess

       :create() only initiates a QQuickWidget(), set some of its 

         properties, connects it to error handeling slots and 

         lays it in a best-judged layout on its parent.

       :setQml( cQml ) is where all the action happens.

          This is the only place where we could know if a QML 

          document has been loaded or not. All subsequest operations 

          are executable only if we succeed here. Be noted that QML 

          engine is a scripting engine and is based on JavaScript 

          heavily.

    Lets disect CLASS HbQtBarcodeReader() and BarcodeReader.qml in 

    relevant context only. HbQtBarcodeReader() is developed to provide 

    one-line calling methodology in mind and has many other constructs

    you are already familiar with.

    METHOD HbQtBarcodeReader:create( oParent )    

       ...

       ...

       // register C++ classes in order to access them inside QML

       // immediately before those are about to be Used

       //

       HBQAbstractVideoSurface():registerQmlTypes()

       QZXing():registerQmlTypes()

      ::oQmlBridge := HbQtQmlBridge():new():create( ::oQmlContainerWidget )

      // provide the QML document location needed

      //

      IF ::oQmlBridge:setQml( "qrc:/hbqtqml/resources/qml/BarcodeReader.qml" )

         ::stopCamera()

         #ifndef __ANDROID__

            // because QVideoProbe() is only available for Android

            // we need render the frame ourselves, so this connection

            //

            ::oQmlBridge:connectChild( "videosurface", "imageAvailable(QImage)", {| oImage | ::dispImage( oImage ) } )

         #endif

         // we could have connected the "qzxing" child also for the same effect

         // but we decided to receive signal via QML document as it implements 

         // more constructs.

         //

         ::oQmlBridge:connect( "tagFound(QString)", {| cTag | ::manageBarcodeFound( cTag ) } )

         __hbqtAppRefresh()

      ENDIF

      ...

      ...

      RETURN self   

   

    BarcodeReader.qml [ only relevant parts ]:

    =========================================

    Rectangle {

        id         : cameraUI

        objectName : "camerainterface"     // name to access the object

                                           // as this is the root object

                                           // it can be accessed directly. 

    

        property bool stopScanningFrames   // can be set/get via :setProperty

    

        signal imageCaptured( string image )

        signal tagFound( string tag )      // signal we will receive via :connect

    

        function startScanning() {

           stopScanningFrames = false;

        }

        function stopScanning() {

           stopScanningFrames = true;

        }

        function stopCamera() {            // method we will invoke via :invokeMethod

            cameraUI.stopScanning();

            camera.stop();

        }

        function startCamera() {

            camera.start();

            cameraUI.startScanning();

            myVideoSurface.decoder = decoder;

            myVideoSurface.source  = camera;

        }

    

        Camera {

            id: camera

            objectName: "camera"           // can be accessed as QObject

                                           // from PRG QObject can only be 

                                           // exploited via :connect()

        }

    

        VideoOutput {

            id               : viewfinder

            objectName       : "viewfinder"

            source           : Qt.platform.os == "android" ? camera : myVideoSurface

        }

    

        QZXing{

            id         : decoder

            objectName : "qzxing"

            onTagFound : {

                if( ! cameraUI.stopScanningFrames )

                {

                    cameraUI.stopScanningFrames = true;

                    playSoundCameraFlash.play();

                    cameraUI.tagFound( tag ); // emit the signal which we :connect()ed

                }

            }

        }

    

        HBQAbstractVideoSurface{

            id         : myVideoSurface

            objectName : "videosurface"   // will connect via :connectChild()

        }

    

        SoundEffect {

            id      : playSoundCameraFlash

            source  : "qrc:/hbqtqml/resources/wav/barcode-beep.wav"

        }

    }

    

    A convinient function, one-liner, can be fired to scan a barcode as:

    __hbqtActivateBarcodeReader( {|cBarcode| LetMePushIntoField( cBarcode ) } )

    I hope this class will flourish with passage of time as we will gain 

    more experience into QML and allied technology. I am impressed with 

    results and plan to share with you whatever meaningful I could muster.

    Enjoy and stay tuned!

Pritpal Bedi

a student of software analysis & concepts