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

nicesw123

Maby the way to do this for now...
(i.e. until the qt developers realize the value of extending QCameraImageProcessing or QCameraViewfinder to allow mirroring (flipping) the image)

...is to "derive from QAbstractVideoSurface" as shown here: http://doc.qt.io/qt-5/cameraoverview.html#viewfinder (find some example code there, showing rotation)

SGaist

DSEngine -> DirectShow. The plugin it self has the control but it seems it's not accessible yet.

If you are wiling to re-build the plugin, that can be modified.

Violet Giraffe

@SGaist, it depends on how difficult it is to build Qt 5 nowadays (I remember it being a pain because of WebKit that I didn't even need, hopefully that's fixed now). Let me check nicesw123's suggestion first.

Devopia53

Qt/C++ already provides that functionality. You can easily implement flipping feature if you use the following classes.

QGraphicsView, QGraphicsScene, QCamera, QVideoWidget, QTramsform

Violet Giraffe

@Devopia53, how can I connect those to QCamera if the only thing camera accepts is QCameraViewfinder?
P. S. Nvm, it accepts QVideoWidget. Still not quite sure how to connect the parts you've listed. A little help, please? :)

Devopia53

@Violet-Giraffe
QCameraViewfinder is not a solution for flipping. Instead, use the QAbstractVideoSurface. But it is poor display performance.

Samples on how to use the QGraphicsView are as follows: I wish you a note.

auto camera = new QCamera;
auto widget = new QVideoWidget;
QTransform matrix(-1,0,0,0,1,0,0,0,1); // m11=-1 : flipping horizontal

graphicsView->setScene(new QGraphicsScene);
graphicsView->show();

auto proxyWidget = graphicsView->scene()->addWidget(widget);

proxyWidget->setTransform(matrix);
camera->setViewfinder(widget);
camera->start();

Violet Giraffe

@Devopia53, thanks, but I think you're missing something. proxyWidget is not used here. AndQTransform has no effect on the widget, although I do see the image just as I did with QCameraViewfinder.

Violet Giraffe

Any further ideas? I'm stuck here.

kshegunov

@Violet-Giraffe

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

Have you tried installing the DX11 SDK?

Violet Giraffe

I have not. Frankly, I doubt this message is related to my task/problem.

SGaist

You don't have to rebuild all of Qt just to modify one module. But the solution I have in mind might not be an optimal use of the API.

HymerB534

@Violet-Giraffe Hi Violet-Giraffe, I've just bought 3 USB wide angle cameras for my van - I was looking at writing an app to display reversing cameras - did you solve the mirroring issue ?

veryqtperson

I've encountered the same necessity - to mirror the video output of the camera.

I found a solution which involves a custom wrapper:

class VideoWrapper : public QAbstractVideoSurface

Then you'll be able to control QVideoSurfaceFormat and perform setMirrored in its start method.

That's actually similar to what @SGaist proposed back then.