Qt Widgets + GStreamer + Overlay + Screen Capture

SeeRich

@SGaist Thank you for looking at this. Are you suggesting that I should change my parameters being passed to drawText(...)?

I am wanting to get rid of the black box behind the overlay text. In this case, it should show yellow text on top of the white, yellow, and cyan vertical stripes from the video.

SGaist

@SeeRich yes, that overload should do what you want directly.

As for the black background, I suspect it's because you set the brush to NoBrush.

SeeRich

@SGaist thank you for your help. I guess I am a little confused.

Is the overload of drawText(...) that you are pointing me to supposed to help me fix the positioning (i.e. centered vertically and horizontally) or is it supposed to fix the black background around the overlay text?

As for the brush, what enumeration would you suggest? I didn't see one that's more equivalent to transparent which I believe is what I want in this case.

I believe the root cause of this issue is because GStreamer is rendering the video to the native window using the video widget's winId() function. It seems to me that the background isn't handled well because this is essentially bypassing Qt to render the video and the background that shows up behind the overlay text is what Qt believes is there (i.e. the MainWindow background).

What do you think?

SeeRich

@SGaist would it be helpful if I provided a CMakeLists.txt file to compile this example code?

JoeCFD

@SeeRich Use a QLabel(not QWidget) as your overlay widget and make it transparent. Then, the black background will be gone.

SeeRich

@JoeCFD Thank you for the suggestion! Unfortunately, it gave me the same result. I specifically changed the overlay code to be this:

class OverlayWidget : public QLabel
{
    Q_OBJECT
public:
    OverlayWidget(QWidget* parent) : QLabel(parent)
    {
        // setAttribute(Qt::WA_TranslucentBackground);
        // setWindowFlags(Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint);
        setStyleSheet("background-color: transparent");
    }

Is this what you were suggesting?

JoeCFD

@SeeRich Yes, something like that. Can you try
setStyleSheet("background-color: green");
to see if the background color is green?

if the green color works, try the following:
QLabel * _overlayLabel{nullptr}; /* no need to create a overlay widget class */
_overlayLabel = new Qlabel( this );
_overlayLabel->setStyleSheet("border:none; background:transparent;");

SeeRich

@JoeCFD The green background did work; however, the _overlayLabel still has a black background. Could this be because Qt isn't aware of what gstreamer is rendering?

JoeCFD

@SeeRich your mainwindow has a black background stylesheet which affects its children. Assign its object name to its stylesheet and its children will not be affected anymore.

    MainWindow()
    {
        resize(720, 600);
        setAttribute(Qt::WA_StyledBackground);
        setObjectName( "mainWindiw" );
        setStyleSheet( QString( "MainWindow#%1 { background-color: black; }" ) .arg( objectName() );

SeeRich

@JoeCFD I really thought that was going to fix it, but unfortunately, same result.

JoeCFD

@SeeRich Change the background-color to blue to make sure the color from mainwindow stylesheet

    MainWindow()
    {
        resize(720, 600);
        setAttribute(Qt::WA_StyledBackground);
        setObjectName( "mainWindow" );
        setStyleSheet( QString( "MainWindow#%1 { background-color: blue; }" ) .arg( objectName() );

also try the following:

_overlayLabel = new Qlabel( this );
_overlayLabel->setAttribute(Qt::WA_StyledBackground);
_overlayLabel->setStyleSheet("border:none; background:transparent;");

SeeRich

@JoeCFD Sorry for the delay...

It is definitely the mainwindow background as the change to blue causes the text background box to change colors as well.

Setting the Qt::WA_StyledBackground attribute didn't change anything either.

JoeCFD

@SeeRich
can you change

        setAttribute(Qt::WA_StyledBackground);
        setObjectName( "mainWindow" );
        setStyleSheet( QString( "MainWindow#%1 { background-color: blue; }" ) .arg( objectName() );

to

        setAttribute(Qt::WA_StyledBackground);
        setObjectName( "mainWindow" );
        setStyleSheet( QString( "QWidget#%1 { background-color: blue; }" ) .arg( objectName() );

there is no MainWindow stylesheet. It should be QMainWindow.