Processing and Displaying Image on Widget

[anda_skoa]

You are creating your QImage on the stack in your render thread, then passing it as a reference to your main window via a signal. Perhaps the crash is because the QImage has gone out of scope by the time the slot receives the reference. Try making the QImage either a member variable of the thread class or passing it by value (so a copy gets made).

No, I think that's ok.
The image copied into a QVariant which is then put into an event and sent to the receiver object's event loop.
While QImage is implicitly shared the "going out of scope" should make the copy inside the variant the only surviving reference and thus safe to access from the main thread.

I have a problem with starting the thread. start function is in my render() routine in my RenderThread class. I have tried to call render routine from various locations in my code, but all of them resulted in crashing right at the startup of my application.

Then you'll have to debug why it crashes.
Not running the image source will not give you any images.

My guess is that you are accessing memory areas that are not valid while looping over the image.
Your inner loop's step size is 1 uint per loop, an uint is usually 4 bytes.
But your image format is one byte per pixel.

Cheers,
_

[mhb88]

My guess is that you are accessing memory areas that are not valid while looping over the image.
Your inner loop's step size is 1 uint per loop, an uint is usually 4 bytes.
But your image format is one byte per pixel.

oh, Wow!! I can't believe that I let this warning confuse me!!

uchar *QImage::scanLine(int i)
Returns a pointer to the pixel data at the scanline with index i. The first scanline is at index 0.
The scanline data is aligned on a 32-bit boundary.
Warning: If you are accessing 32-bpp image data, cast the returned pointer to QRgb* (QRgb has a 32-bit size) and use it to read/write the pixel value. You cannot use the uchar* pointer directly, because the pixel format depends on the byte order on the underlying platform. Use qRed(), qGreen(), qBlue(), and qAlpha() to access the pixels.

thank you very much anda_skoa

cheers

[mhb88]

as you see in my code I posted at the beginning of this thread, I have bunch of classes already in my project and I am going to add a few more as I progress in my project. I came up with the idea to add a TextEdit to my mainwindow.ui and called it Console to display some text there through out my code.
I want to be able to do this from all my classes.
At first I thought there is no easier task than this, but apparently I can't find a solution.
would you guys help me on this?

cheers

[anda_skoa]

You have different options:

- add signals that emit new "console" text to classes that need it and connect to the text edit or a slot in main window
- pass the pointer to the text edit or main window to wherever this is needed
- make the pointer to the text edit or the main window globally accessible

Cheers,
_

[mhb88]

OK, I got everything working as the base of my project. At this point I can communicate with camera, and receive its frames, and just display them in my widget.
But I have an issue.
My camera supports up to 100 frames/sec, but I am barely displaying 15 frames/sec.
My camera resolution is 480x640 and I am just receiving 8bits grayscale frames. So each frame has 480 x 640 x 8 = 300KBytes of data and if I want to receive them at rate of 100 fps, I have to receive them 300KBytes/frame x 100 frames/sec = 30000 KBytes/sec, about 30MBytes/sec, which is half of the speed of the USB2.0. So I think my USB2.0 should be able to do handle that amount of data transfer.

So I think the issue is in my software, but I am not doing any processing in my code, I am just displaying frames. I have created a class with a paint event, and I have promoted a Qwidget to this class to display on it.

I don't know if Qwidget can handle transferring this amount of data?
Does any one has any suggestion or solution?

cheers

[anda_skoa]

For such high througput rendering you probably have to use a more direct rendering approach, e.g. OpenGL.

It might be worthwhile to look into creating a QCamera backend and then use the existing video widget infrastructure.

Cheers,
_

[mhb88]

Do you know any tutorials that start from foundation and builds up to it?
I don't have any experience with OpenGL.
I found most tutorials to be about QGLWidget.
But in the new versions of Qt 5, QOpenGLWidget is intended to be a modern replacement for QGLWidget.
I haven't been able find a good tutorial for QOpenGLWidget.

cheers

[anda_skoa]

No, sorry, I haven't had anything to do with that yet myself either.

Cheers,
_

[mhb88]

I was wondering if this would work?
a function is getting a pointer to a QImage as a parameter.
I want to copy the entire QImage to a buffer of that is going to hold 100 QImages.

public:
    void function(QImage *frame);
 
protected:
    enum{size = 100};
    QImage *data[size];
    int front; // points to the front of the buffer

public:
    void function(QImage *frame);
    
protected:
    enum{size = 100};
    QImage *data[size];
    int front; // points to the front of the buffer

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void Buffer::function(QImage *frame)
{
     ++front; // Increment front.
     if (front == size)
         front = 0; // Wrap around.    
 
     data[front] = frame;
}

void Buffer::function(QImage *frame)
{
     ++front; // Increment front.
     if (front == size)
         front = 0; // Wrap around.    

     data[front] = frame;
}

To copy to clipboard, switch view to plain text mode 

cheers

[anda_skoa]

Sure, why not.
I assume you handle deletion of the QImage pointers somewhere else?

Cheers,
_