QWidget::render() in custom QWidget

J.Hilk

Hello everyone,

I made a custom QStackedWidget with the purpose of an animated transition from one widget to another - Slide in and out.

I had issues with moving the QWidgets directly so I decided to make a screenshot of the new and old widget, show those, and move them with a QParallelAnimationGroup.

I did this the following way:

    QPoint pNext = widget(slideTo)->pos();
    pNow = widget(iCIndex)->pos();

    QPixmap pmCurrent = QPixmap(widget(iCIndex)->size());
    widget(iCIndex)->render(&pmCurrent);
    QPixmap pmSlideTo = QPixmap(widget(slideTo)->size());
    widget(slideTo)->render(&pmSlideTo);

    QLabel *lblCurrent = new QLabel(this);
    QLabel *lblSlideTo = new QLabel(this);
    lblCurrent->resize(widget(iCIndex)->size());
    lblSlideTo->resize(widget(slideTo)->size());
    lblCurrent->show(); lblSlideTo->show();
    
    lblCurrent->setPixmap(pmCurrent);
    lblSlideTo->setPixmap(pmSlideTo);
    lblCurrent->raise();     lblSlideTo->raise();

    lblCurrent->move(0,0);
    lblSlideTo->move(pNext.x() - iOffsetX, pNext.y()-iOffsetY);

    QPropertyAnimation *anCurrent = new QPropertyAnimation(lblCurrent,"pos");
    QPropertyAnimation *anSlideto = new QPropertyAnimation(lblSlideTo,"pos");
    QParallelAnimationGroup *anGroup = new QParallelAnimationGroup;
....
....
    connect(anGroup, &QParallelAnimationGroup::finished, lblCurrent, &QLabel::deleteLater);
    connect(anGroup, &QParallelAnimationGroup::finished, lblSlideTo, &QLabel::deleteLater);

    connect(anGroup, &QParallelAnimationGroup::finished, [=]{
       setCurrentIndex(iNext);
       widget(iNow)->hide();
       widget(iNow)->move(pNow);
       bActive = false;
       emit AnimationFinished();
    });
    anGroup->start();

The problem is, QWidget::render() completely ignores the stylesheet of the cStackedWidget. I applied it with

ui->cStackedMain->setStyleSheet("cStackedWidget{background-color:white;}");

from the GUI-Class. The white background does not show in the QDesigner, but it is correctly painted when I start the program.

If I set a global StyleSheet like

centralWidget->setStyleSheet{background-color:white;}

then render() accepts the white background. However I don't want to/can't use that , because it would overwrite the children of the whole ui.

From the docu I know, that I have the overwrite the paintEvent in my custom widget class, which I did:

void cStackedWidget::paintEvent(QPaintEvent *)
{
    QStyleOption opt;
    opt.init(this);
    QPainter p(this);
    style()->drawPrimitive(QStyle::PE_Widget, &opt, &p, this);
}

So, I'm kinda lost and out of ideas, if anyone could help me, I would be very grateful.

If needed/asked for, I'll look in uploading the class so it can be tested easily!?

mrjj

@J.Hilk

Hi
I think the issue is just who is parent ?
The stylesheet will affect children so if it works with the custom widget when
centralWidget->setStyleSheet{background-color:white;}
has the style so to speak
then it sounds like your custom is just owned by something not affected and hence its children will no either.

I use only a single stylesheet on mainwindow. Not pr control as i think it becomes uncontrollable very fast.

Maybe i misunderstand your issue and what works and what do not work.
Your paint looks correct :)

VRonin

To add to @mrjj

@J.Hilk said in QWidget::render() in custom QWidget:

However I don't want to/can't use that , because it would overwrite the children of the whole ui.

You can use object name specific stylesheet see id selector in http://doc.qt.io/qt-5/stylesheet-syntax.html#selector-types

I had issues with moving the QWidgets directly

I implemented something similar here SelettoreImmagini.h SelettoreImmagini.cpp it's from one of the very first programs I wrote in Qt (a snake game) so it's VERY far from good (and the variable names are in italian) but gives you an idea, basically you keep 1 widget always visible then, you add the widgets that you want to scroll as its children but you never add them to a layout but instead manually resize them to the parent widget, at this point you are free to animate the "pos" property of the child widgets. In the linked example I move 2 QLabels

J.Hilk

@VRonin @mrjj

Hi, sorry for the delay, was a crazy weekend on my side. Thanks for the fast replies

I think I'll have to be more precise with my description.

First off, you may find a small example project here.

So, let's say I set a single StyleSheet on the QMainWindow, like this:

this->setStyleSheet("QMainWindow{background-color:white;}\
                        cStackedWidget{background-color:red;}\
                        QLabel{background-color:blue;}");

I get a exactly what I want, white background/Mainwindow, red Stackedwidget and blue labels.
As soon as I use render() on the first QWidget of the QStackedWidget. the red is completly ignored, I get the default light grey for the stacked widget and blue QLabels

When I set the StyleSheet like this:

this->setStyleSheet("background-color:red;");

Everything is Red but, render() actually captures the QStackedWidget color correctly.

~~LineBreak~~

As I'm writing this, I actually find the crux of the problem.

this:

this->setStyleSheet("QMainWindow{background-color:white;}\
                        cStackedWidget{background-color:red;}\
                        QLabel{background-color:blue;}");

Paints the ui, like I whoud expect it to but its apparently not doing the job thoroughly enough.
Each "page" of the QStackedWidget is a QWidget, and using the above code paints the QWidgets red as well but not for the QWidget::render() function.

Using this StyleSheet:

this->setStyleSheet("QMainWindow{background-color:white;}\
                        cStackedWidget{background-color:red;}\
                        QWidget{background-color:red;}\
                        QLabel{background-color:blue;}");

I see no difference for when the widget is painted, but now QWidget::render actually accepts the red background.

So, is this a bug ot intended behaviour?

mrjj

@J.Hilk
Super with a sample. +5
I see what you mean.
Its a bit odd. So first it accepts the stylesheet but when
you render an image for slide animation it is
not applied. I thought it would be exactly the
same in and render() would just call paint.

Interesting :)

J.Hilk

Just realized, that I had still thread still open.

I'll share how I managed to circumvent the problem. Sadly I haven't found a real solution as of now.

In the function that makes the screenshot, I added this line just before calling QWidget::render

this->setStyleSheet("cStackedWidget {background-color:white;}"
                        "QWidget#LiveStatus{background-color:white;}"
                        ...
                        //List of all  QStackedwidget Pages
                        ...
                        "QWidget#FanThreshhold{background-color:white;}");

For some reason I have to set the stylesheet new for each time. Simply setting this once will not work.

Anyway, I'll mark it as solved,
unless someone else has a new idea !?