《QDebug 2021年4月》

- 日理万妓 2023-01-13 04:28 245阅读 0赞

# 一、Qt Widgets 问题交流 #

### 1. ###

# 二、Qt Quick 问题交流 #

### 1.Control 组件（如 Button 等）的 hoverEnabled 属性 ###

Control2 中 Control 组件（如 Button 等）的 hoverEnabled 属性受到祖先节点该属性设置的影响，如果没有显式设置他就会往上找带这个属性的节点。比如 Button 正好放了个 MouseArea 作为父节点，此时 MouseArea 默认 hoverEnabled = false 就会导致 Button 没有 hover 触发。

源码如下：

bool QQuickControlPrivate::calcHoverEnabled(const QQuickItem *item)
    {
        const QQuickItem *p = item;
        while (p) {
            // QQuickPopupItem accepts hover events to avoid leaking them through.
            // Don't inherit that to the children of the popup, but fallback to the
            // environment variable or style hint.
            if (qobject_cast<const QQuickPopupItem *>(p))
                break;
    
            if (const QQuickControl *control = qobject_cast<const QQuickControl *>(p))
                return control->isHoverEnabled();
    
            QVariant v = p->property("hoverEnabled");
            if (v.isValid() && v.userType() == QMetaType::Bool)
                return v.toBool();
    
            p = p->parentItem();
        }
    
        bool ok = false;
        int env = qEnvironmentVariableIntValue("QT_QUICK_CONTROLS_HOVER_ENABLED", &ok);
        if (ok)
            return env != 0;
    
        // TODO: QQuickApplicationWindow::isHoverEnabled()
    
        return QGuiApplication::styleHints()->useHoverEffects();
    }

### 2.ListView positionViewAtEnd() 没有滚动到底部 ###

参照 Qt Bug：[https://bugreports.qt.io/browse/QTBUG-28474][https_bugreports.qt.io_browse_QTBUG-28474]

有时调用该函数没法滚动到底部，还有一点点距离，解决方法是等到 ListView 的 contentHeight 更改后再调用 positionViewAtEnd()。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2dvbmdqaWFuYm8xOTky_size_16_color_FFFFFF_t_70][]

# 三、其他 #

### 1.Qt 获取 OpenGL 版本 ###

通过 glGetString(GL\_VERSION) 可以获取到 OpenGL 的版本号，但调用这个函数前需要先初始化上下文环境。

Qt 也封装了这个函数，在 QOpenGLFunctions 类中，而构造 QOpenGLContext 上下文还需要一个 QSurface（QWindow 或者 QOffscreenSurface），而 Surface 又需要 QScreen ，QScreen 指针可以通过 QGuiApplication 获取。最终代码如下：

![20210424175916905.png][]

#include <QGuiApplication>
    #include <QQmlApplicationEngine>
    #include <QSurfaceFormat>
    #include <QOpenGLWindow>
    #include <QOpenGLContext>
    #include <QOpenGLFunctions>
    #include <QOffscreenSurface>
    #include <QScreen>
    #include <QDebug>
    
    bool parseOpenGLVersion(const QByteArray &versionString, int &major, int &minor)
    {
        bool majorOk = false;
        bool minorOk = false;
        QList<QByteArray> parts = versionString.split(' ');
        if (versionString.startsWith(QByteArrayLiteral("OpenGL ES"))) {
            if (parts.size() >= 3) {
                QList<QByteArray> versionParts = parts.at(2).split('.');
                if (versionParts.size() >= 2) {
                    major = versionParts.at(0).toInt(&majorOk);
                    minor = versionParts.at(1).toInt(&minorOk);
                    // Nexus 6 has "OpenGL ES 3.0V@95.0 (GIT@I86da836d38)"
                    if (!minorOk)
                        if (int idx = versionParts.at(1).indexOf('V'))
                            minor = versionParts.at(1).left(idx).toInt(&minorOk);
                } else {
                    qWarning("Unrecognized OpenGL ES version");
                }
            } else {
                // If < 3 parts to the name, it is an unrecognised OpenGL ES
                qWarning("Unrecognised OpenGL ES version");
            }
        } else {
            // Not OpenGL ES, but regular OpenGL, the version numbers are first in the string
            QList<QByteArray> versionParts = parts.at(0).split('.');
            if (versionParts.size() >= 2) {
                major = versionParts.at(0).toInt(&majorOk);
                minor = versionParts.at(1).toInt(&minorOk);
            } else {
                qWarning("Unrecognized OpenGL version");
            }
        }
    
        if (!majorOk || !minorOk)
            qWarning("Unrecognized OpenGL version");
        return (majorOk && minorOk);
    }
    
    int main(int argc, char *argv[])
    {
        QCoreApplication::setAttribute(Qt::AA_UseDesktopOpenGL);
    #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
        QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    #endif
    
        QGuiApplication app(argc, argv);
        int major=0;
        int minor=0;
        //一般需要先构造一个QGuiApplication有些函数才能调用
        QScreen *screen=app.primaryScreen();
        if(screen){
            QOffscreenSurface surface(screen);
            surface.create();
            QOpenGLContext context;
            context.create();
            context.makeCurrent(&surface);
    
            const GLubyte *glstr=context.functions()->glGetString(GL_VERSION);
            if(glstr){
               QByteArray bytestr= QByteArray(reinterpret_cast<const char*>(glstr));
               qDebug()<<"glGetString"<<bytestr;
               if(!parseOpenGLVersion(bytestr,major,minor)){
                   major=0;
                   minor=0;
               }
            }
            context.doneCurrent();
            surface.destroy();
        }
        qDebug() << "opengl version:" << major << minor;
    
        QSurfaceFormat format = QSurfaceFormat::defaultFormat();
    
        qDebug() <<"deault format:"<< format;
    
        format.setRenderableType(QSurfaceFormat::OpenGL);
        format.setMajorVersion(3);
        format.setMinorVersion(3);
        format.setProfile(QSurfaceFormat::CoreProfile);
        QSurfaceFormat::setDefaultFormat(format);
    
        qDebug() <<"current format"<< format;
    
        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)
                QCoreApplication::exit(-1);
        }, Qt::QueuedConnection);
        engine.load(url);
    
        return app.exec();
    }

[https_bugreports.qt.io_browse_QTBUG-28474]: https://bugreports.qt.io/browse/QTBUG-28474
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2dvbmdqaWFuYm8xOTky_size_16_color_FFFFFF_t_70]: /images/20221022/21e83d33954e4dcfab248c7851f49f76.png
[20210424175916905.png]: /images/20221022/9c8b2f24f79545c0b1805856682e3728.png