path: root/src/webengine/doc/src/qtwebengine-overview.qdoc

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/*!
    \page qtwebengine-overview.html
    \title Qt WebEngine Overview

    The Qt WebEngine module provides a web browser engine that makes it easy to embed content from
    the World Wide Web into your Qt application on platforms that do not have a native web engine.

    Qt WebEngine provides C++ classes and QML types for rendering HTML, XHTML, and SVG documents,
    styled using Cascading Style Sheets (CSS) and scripted with JavaScript. HTML documents can be
    made fully editable by the user through the use of the \c{contenteditable} attribute on HTML
    elements.

    \section1 Qt WebEngine Architecture

    \image qtwebengine-architecture.png

    The functionality in Qt WebEngine is divided into the following modules:

    \list
        \li \l{Qt WebEngine Widgets Module} for creating widget-based web applications
        \li \l{Qt WebEngine Module} for creating Qt Quick based web applications
        \li \l{Qt WebEngine Core Module} for interacting with Chromium
    \endlist

    Page rendering and JavaScript execution are separated from the GUI process into the Qt WebEngine
    Process. It is a library that must be shipped with the application if the Qt libraries are
    bundled into the application.

    \section2 Qt WebEngine Widgets Module

    \image qtwebenginewidgets-model.png

    A \e {web engine view} is the main widget component of the Qt WebEngine module. It can be used
    in various applications to load web content. Within a view, a \e {web engine page} holds a main
    frame that is responsible for web content, the \e history of navigated links, and \e actions.
    The view and page are quite similar, as they provide a set of common functions.

    All pages belong to a \e {web engine profile} that contains shared \e settings, \e scripts, and
    \e cookies. Profiles can be used to isolate pages from each other. A typical use case is a
    dedicated profile for a \e {private browsing} mode, where no information is permanently saved.

    \note The Qt WebEngine Widgets module uses the \l{Qt Quick Scene Graph}{Qt Quick scene graph}
    to compose the elements of a web page into one view. This means that the UI process
    requires OpenGL ES 2.0 or OpenGL 2.0 for its rendering.

    \section2 Qt WebEngine Module

    \image qtwebengine-model.png

    The Qt WebEngine QML implementation contains the same elements as the Qt WebEngine Widgets
    implementation, except that there is no separately accessible web engine page.
    The supported page functionality is integrated into the web engine view.

    \section2 Qt WebEngine Core Module

    The Qt WebEngine core is based on the \l {Chromium Project}. Chromium provides its own network
    and painting engines and is developed tightly together with its dependent modules.

    \note Qt WebEngine is based on Chromium, but does not contain or use any services
    or add-ons that might be part of the Chrome browser that is built and delivered by Google.
    You can find more detailed information about the differences between Chromium and Chrome in this
    \l{https://chromium.googlesource.com/chromium/src/+/master/docs/chromium_browser_vs_google_chrome.md}{overview}
    that is part of the documentation in the \l {Chromium Project} upstream source tree.

    This version of Qt WebEngine is based on Chromium version 56.0.2924.122, with
    additional security fixes from newer versions.

    \section2 Qt WebEngine Process

    The Qt WebEngine Process is a separate executable that is used to render web pages and
    execute JavaScript. This mitigates security issues and isolates crashes caused by specific
    content.

    \section1 Embedding Web Content into Widget Based Applications

    Use the QWebEngineView class to display web pages in the simplest way. Because it is a widget,
    you can embed QWebEngineView into your forms and use its convenience functions to download and
    display web sites.

    \code
    QWebEngineView *view = new QWebEngineView(parent);
    view->load(QUrl("http://www.qt.io/"));
    view->show();
    \endcode

    An instance of QWebEngineView has one QWebEnginePage. QWebEnginePage can have a
    QWebEngineHistory that provides access to the page's navigation history and several QAction
    objects that apply actions on the web page. In addition, a QWebEnginePage has the ability to
    run JavaScript code in the context of the page's main frame and to enable customization of
    handlers for specific events like showing custom authentication dialogs.

    Each QWebEnginePage belongs to a QWebEngineProfile that can have a QWebEngineSettings
    for specifying page settings, a QWebEngineScriptCollection for running scripts on the page, and
    a QWebEngineCookieStore for accessing the HTTP cookies of Chromium. A QWebEnginePage can also
    directly point to a script collection.

    For a widget based application, the web engine is automatically initialized, unless it is
    placed in a plugin. In that case, it must be initialized in the application main source file
    by using \l QtWebEngine::initialize, as illustrated by the following code snippet:

    \code
    int main(int argc, char **argv)
    {
        QApplication app(argc, argv);

        QtWebEngine::initialize();

        QMainWindow window;
        window.show();

        return app.exec();
    }
    \endcode

    \section1 Embedding Web Content into Qt Quick Applications

    The WebEngineView QML type allows Qt Quick applications to render regions of dynamic web
    content. A \e{WebEngineView} type may share the screen with other QML types or encompass the
    full screen as specified within the Qt Quick application.

    To make sure that OpenGL context can be shared between the GUI and render processes, the web
    engine must be initialized by using \l QtWebEngine::initialize in the application main source
    file, as illustrated by the following code snippet:

    \quotefromfile webengine/minimal/main.cpp
    \skipto main
    \printuntil }

    An application can load pages into the WebEngineView, using either an URL or HTML string, and
    navigate within session history. By default, links to different pages load within the same
    WebEngineView object, but web sites may request them to be opened as a new tab, window, or
    dialog.

    The following sample QML application loads a web page using the \l{WebEngineView::}{url}
    property:

    \quotefromfile webengine/minimal/main.qml
    \skipto import
    \printuntil /^\}/

    \section1 Script Injection

    Qt WebEngine does not allow direct access to the document object model (DOM) of a page.
    However, the DOM can be inspected and adapted by injecting scripts.

    The DOM of a page is constructed when the document is ready, typically
    when the page is completely loaded. Therefore, executing scripts as soon as a document is
    created is not suitable for DOM operations, where one has to wait until the DOM is ready.

    In addition, an injected script shares the same \e world as the other scripts executed on the
    page, which might lead to conflicts. To avoid this, the QWebEngineScript class and the
    WebEngineScript QML type provide implementations of the Chromium API for
    \e{Content Script Extensions}. They specify the
    script to run, the injection point, and the world where the script is run. This enables
    accessing the DOM to manipulate it within a world.

    Since Qt 5.8, Qt WebEngine supports augmenting a script by using the
    following \l{Metadata Block}{Greasemonkey-like attributes}:

    \list
        \li \c {@exclude <regexp>}
        \li \c {@include <regexp>}
        \li \c {@match <regexp>}
        \li \c {@name <free text>}
        \li \c {@run-at [document-start|document-end|document-idle]}
    \endlist

    The attributes determine if and when a \l {User Scripts}{user script} is
    run. They must be placed immediately in the beginning of the script, inside
    a \c ==UserScript== comment:

    \code
    // ==UserScript==
    // @include http://*.qt.io/*
    // @exclude http://wiki.qt.io/*
    // ==/UserScript==

    window.alert("Page is from qt.io, but not wiki.qt.io");
    \endcode

    \section1 Managing Certificates

    Qt WebEngine uses its own network stack, and therefore QSslConfiguration is not used to
    open SSL connections. Instead, Qt WebEngine uses the root CA certificates from the operating
    system to validate the peer's certificate.

    The \l{WebEngineCertificateError::error} and \l{QWebEngineCertificateError::Error} enumerations
    provide information about the types of certificate errors that might occur. The errors can be
    handled by using the WebEngineView::certificateError QML method or by reimplementing the
    QWebEnginePage::certificateError function.

    \section1 Proxy Support

    Qt WebEngine uses the proxy settings from \l{Qt Network}, and forwards them to Chromium's
    networking stack. If QNetworkProxy::applicationProxy is set, it will also be used for Qt
    WebEngine. If QNetworkProxyFactory::usesSystemConfiguration() is enabled, the proxy settings
    are automatically retrieved from the system. Settings from an installed QNetworkProxyFactory
    will be ignored, though.

    Not all properties of QNetworkProxy are supported by Qt WebEngine. That is,
    QNetworkProxy::type(), QNetworkProxy::hostName() and QNetworkProxy::port() are taken into
    account. All other proxy settings such as QNetworkProxy::rawHeader(), QNetworkProxy::user(), or
    QNetworkProxy::password() are ignored.

    If a proxy requires authentication, QWebEnginePage::proxyAuthenticationRequired is emitted.
    For Qt Quick, a dialog is shown.

    \section1 High DPI Support

    To support High DPI devices, it is recommended that the application attribute
    Qt::AA_EnableHighDpiScaling is set to enable automatic scaling based on the
    pixel density of the monitor. In Qt WebEngine applications, the scaling
    affects the default zooming factor and scrollbar size.

    For example:

    \code
    int main(int argc, char *argv[])
    {
      QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
      QApplication app(argc, argv);
      // ...
    }
    \endcode

    Qt WebEngine bundles images for normal and high-dpi resolutions into
    \e qtwebengine_resources_100p.pak and \e qtwebengine_resources_200p.pak
    files. Depending on the target resolutions, one or both of these files need
    to be deployed.

    For more information, see \l{High DPI Displays}.

    \section1 Using WebEngine Core

    Qt WebEngine Core provides an API shared by Qt WebEngine and Qt WebEngine Widgets for handling
    URL requests issued for the networking stack of Chromium and for accessing its HTTP cookies.

    Implementing the QWebEngineUrlRequestInterceptor interface and installing the interceptor on a
    profile enables intercepting, blocking, and modifying URL requests (QWebEngineUrlRequestInfo)
    before they reach the networking stack of Chromium.

    A QWebEngineUrlSchemeHandler can be registered for a profile to add support for custom URL
    schemes. Requests for the scheme are then issued to QWebEngineUrlSchemeHandler::requestStarted()
    as QWebEngineUrlRequestJob objects.

    The QWebEngineCookieStore class provides functions for accessing HTTP cookies of Chromium.
    The functions can be used to synchronize cookies with QNetworkAccessManager, as well as to set,
    delete, and intercept cookies during navigation.

    \section1 Platform Notes

    Qt WebEngine currently supports only Windows, Linux, and \macos. Due to Chromium build
    requirements it also often requires a newer compiler than the rest of Qt. See
    \l{Qt WebEngine Platform Notes} for further details.

    \section1 Related Modules

    Qt WebEngine supersedes the \l{http://doc.qt.io/archives/qt-5.3/qtwebkit-index.html}{Qt WebKit}
    module, which is based on the
    WebKit project, but has not been actively synchronized with the upstream WebKit code since
    Qt 5.2 and has been deprecated in Qt 5.5. For tips on how to change a Qt WebKit widgets
    application to use Qt WebEngine widgets, see \l{Porting from Qt WebKit to Qt WebEngine}.

    The \l{Qt WebView} module allows to use a native web browser on platforms where one is
    available.

    The \l{Qt WebChannel} module can be used to create a bi-directional communication channel
    between QObject objects on the C++ side and JavaScript on the QML side.

*/