QCamera + QCameraViewfinder: how to mirror the the image displayed in the viewfinder?

[SGaist]

You can do some post-processing more easily with QML.

[Violet Giraffe]

Okay then, would it be possible to write my own viewfinder widget that mirrors the image without actually implementing the whole viewfinder by hand myself?

I suppose it's hypothetically possible to make the viewfinder invisible, grab()it on timer (or render it to QPixmap, or whatever), manipulate the image and then draw that image in another, visible widget. But I have serious doubts about performance of this solution. It must work on an Intel Atom PC, and should produce minimal CPU load, too.

[SGaist]

One thing you can try:

1. Get the video surface format of your QCameraViewFinder
2. Call videoSurfaceProperty.setProperty("mirrored", true)
3. Then set it on again.

[Violet Giraffe]

Sorry, but I can't find anything related to video surface format in the QCameraViewFinder class. What's videoSurfaceProperty in your answer?
I can get QCameraViewFinderSettings from QCamera, but that doesn't appear to be what you're referring to. I've looked at the QCameraViewFinderSettings source file and there's no mention of the "mirrored" property.

[SGaist]

No, it's the QVideoRendererControl that you must first retrieve first.

The mirrored property I stumbled upon while checking something unrelated in QtMultimedia's sources.

[Andy314]

Hello @SGaist ,

how can I get the QVideoRenderControl?
From the QViewFinder, which function, I find no.

[Violet Giraffe]

@SGaist, thanks. I, too, can't find a way to get it from QViewFinder (which is a QVideoWidget). Looks like I need QMediaService to get QVideoRenderControl from it.

[SGaist]

QMediaService *mediaService = viewFinder->mediaObject()->service();
QVideoRendererControl *rendererControl = mediaService->requestControl<QVideoRendererControl *>();
rendererControl->setSurface(myVideoSurface);

Don't forget to add the necessary checks.

[Violet Giraffe]

@SGaist
No such luck :( viewFinder->mediaObject() is nullptr.
IS there a restriction on when I should call mediaObject() relative to, say, show() or any other lifecycle-related method of the view finder?

[SGaist]

Did you set the viewFinder on the camera before calling mediaObject ?

[Violet Giraffe]

@SGaist
Nope, i was doing it just before that. So, now I put this code right after setViewfinder, and mediaService is not null, but mediaService->requestControl<QVideoRendererControl *>() returns nullptr.

[SGaist]

What OS are you running ? It might be that the backend doesn't provide that control.

[Violet Giraffe]

Windows 10.

[nicesw123]

how to mirror the the image displayed in the viewfinder?

+1

Actually
+1000

This is a very good question!
I also want to mirror the image (flip it left to right)!

PS:
I'm using Debian Testing, which requires these packages, to get QCamera working: qt5-default, libqt5multimedia5, libqt5multimedia5-plugins, libqt5multimediaquick-p5, libqt5multimediawidgets5, qml-module-qtmultimedia, qtmultimedia5-dbg, qtmultimedia5-dev

[SGaist]

Just a quick update:

    QVideoRendererControl *rendererControl = camera.service()->requestControl<QVideoRendererControl *>();
    if (rendererControl) {
        QAbstractVideoSurface *surface = rendererControl->surface();
        QVideoSurfaceFormat format = surface->surfaceFormat();
        format.setProperty("mirrored", true);

        surface->stop();
        surface->start(format);
    } else {
        qDebug() << "Backend doesn't provide a video renderer control";
    }

[Violet Giraffe]

Thanks, but still no. rendererControl is null, and I tried executing your snippet both before and after camera.start() call.

[SGaist]

Can you check what plugin is loaded ? It should be either the WMF or DirectX plugin. IIRC the DX plugin has the control.

[Violet Giraffe]

I can't see either. Here's the complete list of all the .dlls loaded.
I can, however, see an odd warning. I don't have a slightest idea if it's related, but probably not:

D3D11CreateDevice: Flags (0x2) were specified which require the D3D11 SDK Layers for Windows 10, but they are not present on the system.
These flags must be removed, or the Windows 10 SDK must be installed.
Flags include: D3D11_CREATE_DEVICE_DEBUG

[SGaist]

Sorry, I meant start your application with QT_DEBUG_PLUGINS set to 1.

[Violet Giraffe]

Is it an environment variable or a project define?