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How to change color of the window dynamically?

  • Hi

    I am facing this weird issue. Since the code is part of a big project, I can't post it here. But I will try to give as much as possible. Suppose I have two windows, windowCreator and mainWindow. mainWindow is embedded within windowCreator. No other component or control exists in windowCreator. Below is the WindowCreator.qml

    Window {
        id: windowCreator
        height: 300
        width: 240 
        opacity: 0
        flags: Qt.Tool | Qt.WindowTitleHint | Qt.WindowTransparentForInput
        function createMainWindow() {
            var component = Qt.createComponent(“MainWindow.qml")
            if (component.status === Component.Ready) {
                var mainWindow = component.createObject(windowCreator)
                return mainWindow

    createMainWindow method is called in some other part of the application which launches this window.
    Below is the code for MainWindow.qml

    Window {
        id: mainWindow
        property bool isMinimized: false
        flag: Qt.FramelessWindowHint | Qt.WA_TranslucentBackground | Qt.Window
        color: !isMinimized ? "red" : "transparent"
        opaque: 1

    isMinimized is set from another QML. The problem we are facing here is, based on the value of isMinimized, the color of mainWindow does not change. It always shows black for transparent. It works the other way round, i.e.

    color: isMinimized ? "red" : "transparent"

    But in this case, some part of mainWindow is getting cropped/clipped. We want the code in MainWindow.qml to get working, i.e. the color must change based on the value of isMinimized. The black must be rendered as transparent.

    Experts put in your comments as what mistake am I doing, or what is that I am missing. Surely something is missing and that's why it is acting weird. Let me know if you guys need any further information.

    Thanks in advance.

  • Qt Champions 2017

    isMinimized may not be set by the time you create the object. Can you try setting/change the values in Component.onComplete(...) signal ? Object is constructed by this time.

  • Does the code you posted reproduce the problem? If not can you post minimal code that does?

  • @dheerendra : isMinimized is a property declared in the MainWindow.qml. It's value is set to true when user clicks on minimize button on the customized titlebar. So when mainWindow object is constructed, and when user clicks on minimize button, I need maunwindow's color to be transparent. And red color when it is restored back.

    @fcarney : It's reproducing in my code base, which is based on Qt 5.12. Let me try getting minimal code to reproduce this issue.

  • Qt Champions 2017

    @rakeshthp Are you able to see the problem with sample reproducible program ? If yes, can you send the same ?

  • Hi @dheerendra , @fcarney

    Here is the sample reproducible program. In main.qml, there are four set of statements to set color to the window. All four can be tested one by one. Once you run this, there will be a small black colored rectangle. On clicking that rectangle the background color of the window changes. Below are the observations

    1.    color: "transparent"

    Works fine, I see transparent window

    2.    color: isMinimized ? "red" : "green"

    This also works fine. I see red and green colors alternatively

    3.   color: isMinimized ? "transparent" : "green"

    This one fails: I don't see transparent background while toggling color

    4.   color: !isMinimized ? "transparent" : "green"

    Works fine: I see expected colors while toggling.

    Not sure why #3 is failing, which is exactly we are facing issue in our project.

    So what do you guys think, is missing here or wrong here?

    NOTE: This is tested with Qt 5.12.5 with MSVC2015 on Windows 10 Pro, with Intel(R) Core(TM) i7-6699U CPU@2.60GHz

    Let me know if you guys need any other info.


  • main.qml

    import QtQuick 2.12
    import QtQuick.Window 2.12
    Window {
        property bool isMinimized: false
        flags: Qt.Window | Qt.FramelessWindowHint | Qt.WA_TranslucentBackground
        visible: true
        width: 640
        height: 480
        title: qsTr("Hello World")
    //    color: "transparent"
    //    color: isMinimized ? "red" : "green"
    //    color: isMinimized ? "transparent" : "green"
        color: !isMinimized ? "transparent" : "green"
        Rectangle {
            color: "transparent"
            height: parent.height
            width: parent.width
            anchors.fill: parent
            border.width: 2
            border.color: "blue"
            Rectangle {
                height: parent.height * 0.1
                width: parent.width * 0.02
                color: "black"
                anchors {
                    left: parent.left
                    verticalCenter: parent.verticalCenter
                MouseArea {
                    anchors.fill: parent
                    onClicked: {
                        isMinimized = !isMinimized


    #include <QGuiApplication>
    #include <QQmlApplicationEngine>
    #include <QQuickWindow>
    #include <QPalette>
    int main(int argc, char *argv[])
        QGuiApplication app(argc, argv);
        QPalette palette;
        palette.setColor(QPalette::Base, Qt::transparent);
        QQmlApplicationEngine engine;
        const QUrl url(QStringLiteral("qrc:/main.qml"));
        QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                         &app, [url](QObject *obj, const QUrl &objUrl) {
            if (!obj && url == objUrl)
        }, Qt::QueuedConnection);
        return app.exec();

    .pro file

    QT += quick
    CONFIG += c++11
    # The following define makes your compiler emit warnings if you use
    # any Qt feature that has been marked deprecated (the exact warnings
    # depend on your compiler). Refer to the documentation for the
    # deprecated API to know how to port your code away from it.
    # You can also make your code fail to compile if it uses deprecated APIs.
    # In order to do so, uncomment the following line.
    # You can also select to disable deprecated APIs only up to a certain version of Qt.
    #DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0
    SOURCES += \
    RESOURCES += qml.qrc
    # Additional import path used to resolve QML modules in Qt Creator's code model
    # Additional import path used to resolve QML modules just for Qt Quick Designer
    # Default rules for deployment.
    qnx: target.path = /tmp/$${TARGET}/bin
    else: unix:!android: target.path = /opt/$${TARGET}/bin
    !isEmpty(target.path): INSTALLS += target

  • Qt Champions 2017

    I don't see a issue. I tried your same program. It works fine. I tried with QtQuick 2.14.

    Which platform are you trying ?

  • @dheerendra did you try all four ways of setting colour to the window? Three of them are commented.

  • Qt Champions 2017

    yes. All tried.

  • That's really strange, as I am seeing it in the configuration mentioned above. Are you running it on Windows?

  • @dheerendra : This is tested with Qt 5.12.5 with MSVC2015 on Windows 10 Pro, with Intel(R) Core(TM) i7-6699U CPU@2.60GHz

    @fcarney : Do you also see it working fine?

  • Attached screenshot of issue what I am noticing with this piece of code.


    Thanks in advance

  • @dheerendra ,

    Do you think it may be bug in QtQuick 2.12 ?

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