Blinking background

[Corvette653]

Hi, it will be best to show you my code:

class MyWidget : public QWidget
{
    Q_OBJECT
public:
    MyWidget(QString string1, QString string2, QString string3, QWidget *parent = 0) : QWidget(parent) {
        setAttribute(Qt::WA_StyledBackground);
        QLabel *label1 = new QLabel;
        QLabel *label2 = new QLabel;
        QLabel *label3 = new QLabel;
        QGridLayout *layout = new QGridLayout;

        label1->setText(string1);
        label2->setText(string2);
        label3->setText(string3);
        layout->addWidget(label1, 0, 0);
        layout->addWidget(label2, 1, 0);
        layout->addWidget(label3, 0, 1, 2, 1);

        setLayout(layout);
        setStyleSheet(":hover{background-color: red;}");
    }
    ~MyWidget(){}
};

I make object and show it on the screen. Everything is good, but...
when i leave this object, background-color of one of QLabels (for instance label1) changes a split second earlier than rest of object

1. the whole object is white
2. I move mouse on the object
3. the whole object is red
4. I move mouse off of the object
5. label1 is white, the rest of the object is red
6. the whole object is white

Of course, the problem is stage 5, which I don't want to exist

[mrjj]

@Corvette653
Well that is kinda to be expected as only one widget is actually "hovered" at a given time.
You do see the red all over as labels are transparent so we see the master widget in red under it.

You could add the function to class MyWidget : public QWidget

to handle hover directly and in there then set style sheet to master widget to turn red and
then set style sheet to each label to turn white at same time.

in ctor
this->setAttribute(Qt::WA_HOVER, true);

void MyWidget ::enterEvent(QEvent * event)
{
    // set style sheet
    QWidget::enterEvent(event);
}

void MyWidget ::leaveEvent(QEvent * event)
{
    // other style sheet to return to nomral color for text
    QWidget::leaveEvent(event);
}

https://stackoverflow.com/questions/411823/how-do-i-implement-qhoverevent-in-qt

[SGaist]

Hi,

Which version of Qt are you using ?
On which OS ?

Can you reproduce that with a minimal compilable example ?

[mrjj]

Hi
I tried your code on win 10 with Qt 5.15.1

I didn't not see such an effect so i wonder if you are using a small board or something that draws slowly ?

[Corvette653]

Strange, I can't record it, but it's seeable with the naked eye.
I use Qt 5.14.2 - Windows 10

mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QLabel>
#include <QGridLayout>
#include <QScreen>

class MyWidget : public QWidget
{
    Q_OBJECT
public:
    MyWidget(QString string1, QString string2, QString string3, QWidget *parent = 0) : QWidget(parent) {
        setAttribute(Qt::WA_StyledBackground);
        QLabel *label1 = new QLabel;
        QLabel *label2 = new QLabel;
        QLabel *label3 = new QLabel;
        QGridLayout *layout = new QGridLayout;

        label1->setText(string1);
        label2->setText(string2);
        label3->setText(string3);
        layout->addWidget(label1, 0, 0);
        layout->addWidget(label2, 1, 0);
        layout->addWidget(label3, 0, 1, 2, 1);

        setLayout(layout);
        setStyleSheet(":hover{background-color: red;}");
    }
    ~MyWidget(){}
};

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow();
    ~MainWindow();

    QLabel *spacer1 = new QLabel;
    MyWidget *widget1 = new MyWidget("text aaaaaaaaa", "text bbbbbbbb", "text ccccccc");
    MyWidget *widget2 = new MyWidget("text aaaaaaaaa", "text bbbbbbbb", "text ccccccc");
    MyWidget *widget3 = new MyWidget("text aaaaaaaaa", "text bbbbbbbb", "text ccccccc");
    QLabel *spacer2 = new QLabel;
    QGridLayout *layout = new QGridLayout;
    QWidget *central = new QWidget;
};
#endif // MAINWINDOW_H

mainwindow.cpp:

#include "mainwindow.h"

MainWindow::MainWindow() {
    showMaximized();
    setGeometry(screen()->geometry());

    layout->addWidget(spacer1);
    layout->addWidget(widget1);
    layout->addWidget(widget2);
    layout->addWidget(widget3);
    layout->addWidget(spacer2);
    central->setLayout(layout);
    setCentralWidget(central);
}
MainWindow::~MainWindow() {}

Like I said earlier it's a split second, but I have list which is made of these objects. When each of them 'blinks', it looks really bad.
Is it possible, that my computer/screen is the reason?

[Corvette653]

I recorded it by my phone, I can't insert video here, so it's link to my google drive:
video

[mrjj]

@Corvette653
Ok that looks indeed odd.

• Is it possible, that my computer/screen is the reason?
  well it would have to be a really, really old flat screen for it to be the redraw time.

I can see you have multiply MyWidets on screen.

I only tried one. let me see with more.

[mrjj]

Hi
Nope even with your new test code
and full screen window size i dont get that effect.

Could you try

    label1->setAutoFillBackground(false);
    label2->setAutoFillBackground(false);
    label3->setAutoFillBackground(false);

inside myWidget ?
Should be off but just to be sure.

[Corvette653]

@mrjj, I don't know how it was set originally, but adding "setAutoFillBackground" changes nothing :/
Edit: I ran this app on another computer and it's visible there too.

[mrjj]

@Corvette653
Hi
Ok, was the only thing i could think of.

Im not sure what you see.
If you move mouse more slowly, does it also happen ?

[Corvette653]

@mrjj
Me neither.
When I move mouse very slow, everything is alright.
How often is it checked if mouse is over widget?
Is it possible that it happens when I move mouse: label -> out of widget,
but if I move: margin -> out of widget, everything is ok?

[mrjj]

@Corvette653
Hi
I think on every mouse move event as to check its still over it.
Well both the main Widget and the Labels are affected by your stylesheet but
Labels are transparent so not sure it would do so much.

But yes from the video , it does seem related to the labels background as the
white ghost thing seems to be where the labels are.

[Corvette653]

:/ It's strange, I wanted to change font color, of the whole widget(3 labels), but it doesn't work in the way I want

setStyleSheet(":hover{background-color: red; color: white;}");

[mrjj]

Hi
What happens ?

[Corvette653]

Only label I directly hover has the white text, I want the whole widget to has.
Background color is set in the same line, but works good (except that strange white ghosts which I have already ignored)

[mrjj]

@Corvette653
Well that is kinda to be expected as only one widget is actually "hovered" at a given time.
You do see the red all over as labels are transparent so we see the master widget in red under it.

You could add the function to class MyWidget : public QWidget

to handle hover directly and in there then set style sheet to master widget to turn red and
then set style sheet to each label to turn white at same time.

in ctor
this->setAttribute(Qt::WA_HOVER, true);

void MyWidget ::enterEvent(QEvent * event)
{
    // set style sheet
    QWidget::enterEvent(event);
}

void MyWidget ::leaveEvent(QEvent * event)
{
    // other style sheet to return to nomral color for text
    QWidget::leaveEvent(event);
}

https://stackoverflow.com/questions/411823/how-do-i-implement-qhoverevent-in-qt

[Corvette653]

@mrjj
Maybe it's not exactly answear to first question, but it resolves that.
I moved bckground-color to those functions and it works correctly

[mrjj]

@Corvette653
Hi
well it's not really possible to hover more than one widget at a time so
pure style sheet would not be able to make all labels use white on hover.