Move printing operation to a new thread

Printing operations were blocking the UI thread, so applications
were irresponsive when printing in large size or high resolution.
Introduce a new worker for the painting logic and use shared pointers
to carry the data around and avoid copying PDF data between threads.

Task-number: QTBUG-68561
Change-Id: I30633380b75acd14f1a1df87985c99540168a9f1
Reviewed-by: Michael Brüning <michael.bruning@qt.io>

5 files changed, 262 insertions, 90 deletions

diff --git a/src/webenginewidgets/api/qwebenginepage.cpp b/src/webenginewidgets/api/qwebenginepage.cpp
index 6a70203be..751f31462 100644
--- a/src/webenginewidgets/api/qwebenginepage.cpp
+++ b/src/webenginewidgets/api/qwebenginepage.cpp
@@ -48,7 +48,7 @@
 #include "file_picker_controller.h"
 #include "javascript_dialog_controller.h"
 #if QT_CONFIG(webengine_printing_and_pdf)
-#include "printing/pdfium_document_wrapper_qt.h"
+#include "printer_worker.h"
 #endif
 #include "qwebenginecertificateerror.h"
 #include "qwebenginefullscreenrequest.h"
@@ -94,6 +94,7 @@
 #include <QMimeData>
 #if QT_CONFIG(webengine_printing_and_pdf)
 #include <QPrinter>
+#include <QThread>
 #endif
 #include <QStandardPaths>
 #include <QStyle>
@@ -106,89 +107,6 @@ using namespace QtWebEngineCore;
 
 static const int MaxTooltipLength = 1024;
 
-#if QT_CONFIG(webengine_printing_and_pdf)
-static bool printPdfDataOnPrinter(const QByteArray& data, QPrinter& printer)
-{
-    if (!data.size()) {
-        qWarning("Failure to print on printer %ls: Print result data is empty.",
-                 qUtf16Printable(printer.printerName()));
-        return false;
-    }
-
-    QSize pageSize = printer.pageRect().size();
-    PdfiumDocumentWrapperQt pdfiumWrapper(data.constData(), data.size(), pageSize);
-
-    int toPage = printer.toPage();
-    int fromPage = printer.fromPage();
-    bool ascendingOrder = true;
-
-    if (fromPage == 0 && toPage == 0) {
-        fromPage = 1;
-        toPage = pdfiumWrapper.pageCount();
-    }
-    fromPage = qMax(1, fromPage);
-    toPage = qMin(pdfiumWrapper.pageCount(), toPage);
-
-    if (printer.pageOrder() == QPrinter::LastPageFirst) {
-        qSwap(fromPage, toPage);
-        ascendingOrder = false;
-    }
-
-    int pageCopies = 1;
-    int documentCopies = 1;
-
-    if (!printer.supportsMultipleCopies())
-        documentCopies = printer.copyCount();
-
-    if (printer.collateCopies()) {
-        pageCopies = documentCopies;
-        documentCopies = 1;
-    }
-
-    QPainter painter;
-    if (!painter.begin(&printer)) {
-        qWarning("Failure to print on printer %ls: Could not open printer for painting.",
-                  qUtf16Printable(printer.printerName()));
-        return false;
-    }
-
-    for (int printedDocuments = 0; printedDocuments < documentCopies; printedDocuments++) {
-        int currentPageIndex = fromPage;
-        while (true) {
-            for (int printedPages = 0; printedPages < pageCopies; printedPages++) {
-                if (printer.printerState() == QPrinter::Aborted
-                        || printer.printerState() == QPrinter::Error)
-                    return false;
-
-                QImage currentImage = pdfiumWrapper.pageAsQImage(currentPageIndex - 1);
-                if (currentImage.isNull())
-                    return false;
-
-                // Painting operations are automatically clipped to the bounds of the drawable part of the page.
-                painter.drawImage(QRect(0, 0, pageSize.width(), pageSize.height()), currentImage, currentImage.rect());
-                if (printedPages < pageCopies - 1)
-                    printer.newPage();
-            }
-
-            if (currentPageIndex == toPage)
-                break;
-
-            if (ascendingOrder)
-                currentPageIndex++;
-            else
-                currentPageIndex--;
-
-            printer.newPage();
-        }
-        if (printedDocuments < documentCopies - 1)
-            printer.newPage();
-    }
-    painter.end();
-
-    return true;
-}
-#endif // QT_CONFIG(webengine_printing_and_pdf)
-
 static QWebEnginePage::WebWindowType toWindowType(WebContentsAdapterClient::WindowOpenDisposition disposition)
 {
     switch (disposition) {
@@ -502,19 +420,35 @@ void QWebEnginePagePrivate::didFindText(quint64 requestId, int matchCount)
     m_callbacks.invoke(requestId, matchCount > 0);
 }
 
-void QWebEnginePagePrivate::didPrintPage(quint64 requestId, const QByteArray &result)
+void QWebEnginePagePrivate::didPrintPage(quint64 requestId, QSharedPointer<QByteArray> result)
 {
 #if QT_CONFIG(webengine_printing_and_pdf)
+    Q_Q(QWebEnginePage);
+
     // If no currentPrinter is set that means that were printing to PDF only.
     if (!currentPrinter) {
-        m_callbacks.invoke(requestId, result);
+        if (!result.data())
+            return;
+        m_callbacks.invoke(requestId, *(result.data()));
         return;
     }
 
-    bool printerResult = printPdfDataOnPrinter(result, *currentPrinter);
+    QThread *printerThread = new QThread;
+    QObject::connect(printerThread, &QThread::finished, printerThread, &QThread::deleteLater);
+    printerThread->start();
+
+    PrinterWorker *printerWorker = new PrinterWorker(result, currentPrinter);
+    QObject::connect(printerWorker, &PrinterWorker::resultReady, q, [=](bool success) {
+        currentPrinter = nullptr;
+        m_callbacks.invoke(requestId, success);
+    });
+
+    QObject::connect(printerWorker, &PrinterWorker::resultReady, printerThread, &QThread::quit);
+    QObject::connect(printerThread, &QThread::finished, printerWorker, &PrinterWorker::deleteLater);
+
+    printerWorker->moveToThread(printerThread);
+    QMetaObject::invokeMethod(printerWorker, "print");
 
-    currentPrinter = nullptr;
-    m_callbacks.invoke(requestId, printerResult);
 #else
     // we should never enter this branch, but just for safe-keeping...
     Q_UNUSED(result);
diff --git a/src/webenginewidgets/api/qwebenginepage_p.h b/src/webenginewidgets/api/qwebenginepage_p.h
index 7b4e52f79..ddd9e8342 100644
--- a/src/webenginewidgets/api/qwebenginepage_p.h
+++ b/src/webenginewidgets/api/qwebenginepage_p.h
@@ -124,7 +124,7 @@ public:
     void didFetchDocumentMarkup(quint64 requestId, const QString& result) override;
     void didFetchDocumentInnerText(quint64 requestId, const QString& result) override;
     void didFindText(quint64 requestId, int matchCount) override;
-    void didPrintPage(quint64 requestId, const QByteArray &result) override;
+    void didPrintPage(quint64 requestId, QSharedPointer<QByteArray> result) override;
     void didPrintPageToPdf(const QString &filePath, bool success) override;
     void passOnFocus(bool reverse) override;
     void javaScriptConsoleMessage(JavaScriptConsoleMessageLevel level, const QString& message, int lineNumber, const QString& sourceID) override;
diff --git a/src/webenginewidgets/printer_worker.cpp b/src/webenginewidgets/printer_worker.cpp
new file mode 100644
index 000000000..3a670ad49
--- /dev/null
+++ b/src/webenginewidgets/printer_worker.cpp
@@ -0,0 +1,147 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtWebEngine module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "printer_worker.h"
+
+#include "printing/pdfium_document_wrapper_qt.h"
+
+#include <QPainter>
+#include <QPrinter>
+
+namespace QtWebEngineCore {
+
+PrinterWorker::PrinterWorker(QSharedPointer<QByteArray> data, QPrinter *printer)
+    : m_data(data)
+    , m_printer(printer)
+{
+}
+
+PrinterWorker::~PrinterWorker()
+{
+}
+
+void PrinterWorker::print()
+{
+    if (!m_data->size()) {
+        qWarning("Failure to print on printer %ls: Print result data is empty.",
+                 qUtf16Printable(m_printer->printerName()));
+        Q_EMIT resultReady(false);
+        return;
+    }
+
+    QSize pageSize = m_printer->pageRect().size();
+    PdfiumDocumentWrapperQt pdfiumWrapper(m_data->constData(), m_data->size(), pageSize);
+
+    int toPage = m_printer->toPage();
+    int fromPage = m_printer->fromPage();
+    bool ascendingOrder = true;
+
+    if (fromPage == 0 && toPage == 0) {
+        fromPage = 1;
+        toPage = pdfiumWrapper.pageCount();
+    }
+    fromPage = qMax(1, fromPage);
+    toPage = qMin(pdfiumWrapper.pageCount(), toPage);
+
+    if (m_printer->pageOrder() == QPrinter::LastPageFirst) {
+        qSwap(fromPage, toPage);
+        ascendingOrder = false;
+    }
+
+    int pageCopies = 1;
+    int documentCopies = 1;
+
+    if (!m_printer->supportsMultipleCopies())
+        documentCopies = m_printer->copyCount();
+
+    if (m_printer->collateCopies()) {
+        pageCopies = documentCopies;
+        documentCopies = 1;
+    }
+
+    QPainter painter;
+    if (!painter.begin(m_printer)) {
+        qWarning("Failure to print on printer %ls: Could not open printer for painting.",
+                  qUtf16Printable(m_printer->printerName()));
+        Q_EMIT resultReady(false);
+        return;
+    }
+
+    for (int printedDocuments = 0; printedDocuments < documentCopies; printedDocuments++) {
+        int currentPageIndex = fromPage;
+        while (true) {
+            for (int printedPages = 0; printedPages < pageCopies; printedPages++) {
+                if (m_printer->printerState() == QPrinter::Aborted
+                        || m_printer->printerState() == QPrinter::Error) {
+                    Q_EMIT resultReady(false);
+                    return;
+                }
+
+                QImage currentImage = pdfiumWrapper.pageAsQImage(currentPageIndex - 1);
+                if (currentImage.isNull()) {
+                    Q_EMIT resultReady(false);
+                    return;
+                }
+
+                // Painting operations are automatically clipped to the bounds of the drawable part of the page.
+                painter.drawImage(QRect(0, 0, pageSize.width(), pageSize.height()), currentImage, currentImage.rect());
+                if (printedPages < pageCopies - 1)
+                    m_printer->newPage();
+            }
+
+            if (currentPageIndex == toPage)
+                break;
+
+            if (ascendingOrder)
+                currentPageIndex++;
+            else
+                currentPageIndex--;
+
+            m_printer->newPage();
+        }
+        if (printedDocuments < documentCopies - 1)
+            m_printer->newPage();
+    }
+    painter.end();
+
+    Q_EMIT resultReady(true);
+    return;
+}
+
+} // namespace QtWebEngineCore
diff --git a/src/webenginewidgets/printer_worker.h b/src/webenginewidgets/printer_worker.h
new file mode 100644
index 000000000..96025c90e
--- /dev/null
+++ b/src/webenginewidgets/printer_worker.h
@@ -0,0 +1,88 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtWebEngine module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#ifndef PRINTER_WORKER_H
+#define PRINTER_WORKER_H
+
+#include "qtwebenginecoreglobal_p.h"
+
+#include <QSharedPointer>
+
+QT_BEGIN_NAMESPACE
+class QPrinter;
+QT_END_NAMESPACE
+
+namespace QtWebEngineCore {
+
+class PrinterWorker : public QObject
+{
+    Q_OBJECT
+public:
+    PrinterWorker(QSharedPointer<QByteArray> data, QPrinter *printer);
+    virtual ~PrinterWorker();
+
+public Q_SLOTS:
+    void print();
+
+Q_SIGNALS:
+    void resultReady(bool success);
+
+private:
+    Q_DISABLE_COPY(PrinterWorker)
+
+    QSharedPointer<QByteArray> m_data;
+    QPrinter *m_printer;
+};
+
+} // namespace QtWebEngineCore
+
+Q_DECLARE_METATYPE(QtWebEngineCore::PrinterWorker*)
+
+#endif // PRINTER_WORKER_H
diff --git a/src/webenginewidgets/webenginewidgets.pro b/src/webenginewidgets/webenginewidgets.pro
index e61575d3a..4669c2bce 100644
--- a/src/webenginewidgets/webenginewidgets.pro
+++ b/src/webenginewidgets/webenginewidgets.pro
@@ -49,6 +49,9 @@ HEADERS = \
 
 qtConfig(webengine-printing-and-pdf) {
     QT += printsupport
+
+    SOURCES += printer_worker.cpp
+    HEADERS += printer_worker.h
 }
 
 load(qt_module)