// Copyright (C) 2019 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \example webenginewidgets/printme
    \examplecategory {Web Technologies}
    \title WebEngine Widgets PrintMe Example
    \ingroup webengine-widgetexamples
    \brief Demonstrates how to print web pages using Qt WebEngine Widgets.

    \image printme-example.png

    \e PrintMe demonstrates how to use the \l{QWebEnginePage} and
    \l{QPrintDialog} classes to print a web page. Further, it shows how
    to implement print preview by using the \l{QPrintPreviewDialog} class.
    For completeness, it also illustrates how to trigger a printing request
    within JavaScript.

    \include examples-run.qdocinc

    \section1 Simple HTML Page

    In this example, we create an internal HTML page that is added as a resource
    collection file (.qrc). The page shows only a small HTML message box that
    explains how to trigger printing by using keyboard shortcuts or clicking a
    button. The button has the JavaScript \c{onclick} event attribute that calls
    the JavaScript \c{window.print()} function.

    \quotefromfile webenginewidgets/printme/data/index.html
    \skipto <html
    \printuntil html>

    \section1 Main Function

    In the \c main function, we first instantiate a QWebEngineView and set the
    URL to our internal HTML page. Next, we create a \c PrintHandler instance
    and pass the requested page. For convenience, we also create keyboard
    shortcuts that can be used to call a print dialog or print preview dialog.

    \quotefromfile webenginewidgets/printme/main.cpp
    \skipto QWebEngineView view
    \printto return

    \section1 Print Handler

    In the \c{PrintHandler} class, we first implement \c{printPreview()},
    where we instantiate \l{QPrintPreviewDialog}.
    We need the \l{QPrintPreviewDialog::paintRequested} handle to generate a
    set of preview pages.

    \quotefromfile webenginewidgets/printme/printhandler.cpp
    \skipto PrintHandler::printPreview(
    \printuntil /^\}/

    Now we can implement the \c{PrintHandler::printDocument()} slot, which is
    called in response to the \l{QPrintPreviewDialog::paintRequested} signal.
    To do actual painting on a printer, we call the \l QWebEngineView::print()
    function. Printing is an async operation in Chromium, but not in Qt, so we
    run a local event loop using \l{QEventLoop::exec()} to make sure printing
    is done before returning. User input is blocked, since clicking on a button
    while we're waiting for the print to finish can mess up the internal state
    and cause a crash.

    \quotefromfile webenginewidgets/printme/printhandler.cpp
    \skipto PrintHandler::printDocument(
    \printuntil /^\}/

    To get notified about the result of printing job, we implement
    \c{PrintHandler::printFinished()} slot as handler of
    \l QWebEngineView::printFinished() signal. We check for \c{success} and
    report any errors that occurred. Finally, we call \l{QEventLoop::quit()}
    to exit out of the local event loop.

    \quotefromfile webenginewidgets/printme/printhandler.cpp
    \skipto PrintHandler::printFinished(
    \printuntil /^\}/

    The last function we implement, \c{PrintHandler::print()}, is trivial,
    because it simply opens \l{QPrintDialog} and calls the previously
    implemented \c{PrintHandler::printDocument()}.

    \quotefromfile webenginewidgets/printme/printhandler.cpp
    \skipto PrintHandler::print(
    \printuntil /^\}/
*/
