QThreads - queued connections

[freekill]

I'm trying to pass on a QImage from a worker thread (renderingThread) to my main thread for painting. Most of the code I used are recycled from the Mandelbrot Example. However, I'm getting an error from the emitted signal from my rendering thread.

In member function 'virtual void RenderingThread::run()' : error: no matching function for call to 'RenderingThread::renderedImage(QImage*)' candidates are: void RenderingThread::renderedImage(QImage&)

I'm passing along a reference to a QImage and not a pointer. Even the call to my function takes a reference and not a pointer. Here's some codes.

//webcam.cpp
   renderingThread = new RenderingThread(imagebuffer,waitcondition) //thread is given pointers to a buffer and a wait condition
 
   qRegisterMetaType<QImage>("QImage");
   connect(&renderingThread, SIGNAL(renderedImage(QImage& )), this, SLOT(updatePixmap(QImage& )));
   connect(startButton, SIGNAL(clicked()), this, SLOT(startThreads()));
 
//renderingthread.h
signals:
       void renderedImage(QImage& displayImage);
private:
      QImage displayImage;
 
//renderingthread.cpp
void RenderingThread::run(){
while (!halt){
        //rendering process()...
	emit renderedImage(&displayImage);
        }
}

//webcam.cpp
   renderingThread = new RenderingThread(imagebuffer,waitcondition) //thread is given pointers to a buffer and a wait condition

   qRegisterMetaType<QImage>("QImage");
   connect(&renderingThread, SIGNAL(renderedImage(QImage& )), this, SLOT(updatePixmap(QImage& )));
   connect(startButton, SIGNAL(clicked()), this, SLOT(startThreads()));

//renderingthread.h
signals:
       void renderedImage(QImage& displayImage);
private:
      QImage displayImage;

//renderingthread.cpp
void RenderingThread::run(){
while (!halt){
        //rendering process()...
	emit renderedImage(&displayImage);
        }
}

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What could be wrong?

[wysota]

You are passing a pointer:

emit renderedImage(&displayImage);

emit renderedImage(&displayImage);

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To pass a reference simply do:

emit renderedImage(displayImage);

emit renderedImage(displayImage);

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The compiler will know it should pass a reference and not a copy by looking at the signature of the method.

[freekill]

Thanks. I guess I'm getting closer to my results however,

emit renderedImage(displayImage);

emit renderedImage(displayImage);

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is now giving me this error:
undefined reference to 'RenderingThread::renderedImage(QImage&)'

[wysota]

You either didn't declare the signal or you forgot the Q_OBJECT macro in your class header.

[faldzip]

//webcam.cpp
   renderingThread = new RenderingThread(imagebuffer,waitcondition) //thread is given pointers to a buffer and a wait condition
 
   qRegisterMetaType<QImage>("QImage");
   connect(&renderingThread, SIGNAL(renderedImage(QImage& )), this, SLOT(updatePixmap(QImage& )));

//webcam.cpp
   renderingThread = new RenderingThread(imagebuffer,waitcondition) //thread is given pointers to a buffer and a wait condition

   qRegisterMetaType<QImage>("QImage");
   connect(&renderingThread, SIGNAL(renderedImage(QImage& )), this, SLOT(updatePixmap(QImage& )));

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What could be wrong?

renderingThread is already a pointer so &renderingThread is a pointer to pointer (type RenderingThread**) - I guess it is not what you want. Just pass renderingThread to connect() method.