c++ - 为什么使用 QQuickWindow::grabWindow() 会导致窗口变成图像？

Question

我有一个 QQuickWidget，想使用 QQuickWindow::grabWindow() 抓取屏幕截图。但是，当我这样做时，QQuickWindow 变成了图像并且没有响应。

下面是一个最小的可重现代码:该错误在 Qt5.13 到 Qt5.15.1 的 Release模式下可重现(由于某种原因 Qt 在调试中抛出断言)

//TestWidget.pro

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets quickwidgets

CONFIG += c++11

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
    main.cpp \
    mainwindow.cpp

HEADERS += \
    mainwindow.h \
    windowgrabber.h

FORMS += \
    mainwindow.ui

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

DISTFILES += \
    Main.qml

RESOURCES += \
    qml.qrc

// main.cpp

#include <QApplication>
#include <QQuickWidget>
#include <QQmlContext>
#include "windowgrabber.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QQuickWidget *quickWidget = new QQuickWidget;
    quickWidget->rootContext()->setContextProperty("windowGrabber", new WindowGrabber(quickWidget));
    quickWidget->setSource(QUrl("qrc:/Main.qml"));
    quickWidget->show();

    return a.exec();
}

//主.qml

import QtQuick 2.0
import QtQuick.Controls 2.0

Page {
    Button {
        id: button
        text: "grab window"
        onClicked: windowGrabber.grabWindow(button)
    }
}

//WindowGrabber.h

#ifndef WINDOWGRABBER_H
#define WINDOWGRABBER_H

#include <QObject>
#include <QQuickItem>
#include <QQuickWindow>

class WindowGrabber : public QObject
{
    Q_OBJECT
public:
    WindowGrabber(QObject *parent = nullptr) : QObject(parent) {}
    Q_INVOKABLE static void grabWindow(QQuickItem *item) {
        item->window()->grabWindow();
    }
};

#endif // WINDOWGRABBER_H

代码创建了一个 QQuickWidget，源设置为 Main.qml。单击 qml 中的按钮时，我想截屏。但是单击按钮后，快速小部件内的 QQuickWindow 变成图像，按钮也变成图像。我已经使用 QWidget::createWindowContainer 进行了测试并且它有效，但最好的解决方案是使用 QQuickWidget。有人知道为什么会发生这种情况吗？

Answer 1

QQuickWidget 使用不可见的 QQuickWindow 来呈现项目，并且该呈现在 QWidget 中再次呈现，因此在尝试保存图像时它会干扰，导致延迟，正如我已经在 this post 中指出的那样.

一种可能的解决方案是直接从 QQuickWidget 中抓取:

#ifndef WINDOWGRABBER_H
#define WINDOWGRABBER_H

#include <QObject>
#include <QQuickWidget>

class WindowGrabber : public QObject
{
    Q_OBJECT
public:
    WindowGrabber(QQuickWidget *widget): m_widget(widget)  {}
    Q_INVOKABLE void grabWindow() {
        if(m_widget){
            QPixmap img = m_widget->grab();
            qDebug() << img;
        }
    }
private:
    QPointer<QQuickWidget> m_widget;
};


#endif // WINDOWGRABBER_H

#include <QApplication>
#include <QQuickWidget>
#include <QQmlContext>
#include "windowgrabber.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QQuickWidget quickWidget;
    WindowGrabber grabber(&quickWidget);
    quickWidget.rootContext()->setContextProperty("windowGrabber", &grabber);
    quickWidget.setSource(QUrl("qrc:/main.qml"));
    quickWidget.show();

    return a.exec();
}

Button {
    id: button
    text: "grab window"
    onClicked: windowGrabber.grabWindow()
}