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diff --git a/src/gui/kernel/qhighdpiscaling.cpp b/src/gui/kernel/qhighdpiscaling.cpp
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+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtGui 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 Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/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 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qhighdpiscaling_p.h"
+#include "qguiapplication.h"
+#include "qscreen.h"
+#include "qplatformintegration.h"
+#include "private/qscreen_p.h"
+
+#include <QtCore/qdebug.h>
+
+QT_BEGIN_NAMESPACE
+
+Q_LOGGING_CATEGORY(lcScaling, "qt.scaling");
+
+static const char legacyDevicePixelEnvVar[] = "QT_DEVICE_PIXEL_RATIO";
+static const char scaleFactorEnvVar[] = "QT_SCALE_FACTOR";
+static const char autoScreenEnvVar[] = "QT_AUTO_SCREEN_SCALE_FACTOR";
+
+static inline qreal initialScaleFactor()
+{
+
+    qreal result = 1;
+    if (qEnvironmentVariableIsSet(scaleFactorEnvVar)) {
+        bool ok;
+        const qreal f = qgetenv(scaleFactorEnvVar).toDouble(&ok);
+        if (ok && f > 0) {
+            qCDebug(lcScaling) << "Apply " << scaleFactorEnvVar << f;
+            result = f;
+        }
+    } else {
+        if (qEnvironmentVariableIsSet(legacyDevicePixelEnvVar)) {
+            qWarning() << "Warning:" << legacyDevicePixelEnvVar << "is deprecated. Instead use:";
+            qWarning() << "   " << scaleFactorEnvVar << "to set the application global scale factor.";
+            qWarning() << "   " << autoScreenEnvVar << "to enable platform plugin controlled per-screen factors.";
+
+            int dpr = qEnvironmentVariableIntValue(legacyDevicePixelEnvVar);
+            if (dpr > 0)
+                result = dpr;
+        }
+    }
+    return result;
+}
+
+/*!
+    \class QHighDpiScaling
+    \since 5.6
+    \internal
+    \preliminary
+    \ingroup qpa
+
+    \brief Collection of utility functions for UI scaling.
+*/
+
+
+qreal QHighDpiScaling::m_factor;
+
+bool QHighDpiScaling::m_active; //"overall active" - is there any scale factor set.
+bool QHighDpiScaling::m_perScreenActive; // different screens may have different scale
+bool QHighDpiScaling::m_usePixelDensity; // use scale factor from platform plugin
+
+void QHighDpiScaling::initHighDPiScaling()
+{
+    m_factor = initialScaleFactor();
+    bool usePlatformPluginPixelDensity = qEnvironmentVariableIsSet(autoScreenEnvVar)
+                                         || qgetenv(legacyDevicePixelEnvVar).toLower() == "auto";
+
+    // m_active below is "overall active" - is there any scale factor set.
+    m_active = !qFuzzyCompare(m_factor, qreal(1)) || usePlatformPluginPixelDensity;
+    m_usePixelDensity = usePlatformPluginPixelDensity;
+    m_perScreenActive = m_usePixelDensity;
+}
+
+/*
+    Sets the global scale factor which is applied to all windows.
+*/
+void QHighDpiScaling::setGlobalFactor(qreal factor)
+{
+    if (qFuzzyCompare(factor, QHighDpiScaling::m_factor))
+        return;
+    if (!QGuiApplication::allWindows().isEmpty()) {
+        qWarning() << Q_FUNC_INFO << "QHighDpiScaling::setFactor: Should only be called when no windows exist.";
+    }
+
+    QHighDpiScaling::m_active = !qFuzzyCompare(factor, qreal(1));
+    QHighDpiScaling::m_factor = QHighDpiScaling::m_active ? factor : qreal(1);
+    Q_FOREACH (QScreen *screen, QGuiApplication::screens())
+         screen->d_func()->updateHighDpi();
+}
+
+static const char *scaleFactorProperty = "_q_scaleFactor";
+
+/*
+    Sets a per-screen scale factor.
+*/
+void QHighDpiScaling::setScreenFactor(QScreen *screen, qreal factor)
+{
+    m_active = true;
+    m_perScreenActive = true;
+    screen->setProperty(scaleFactorProperty, QVariant(factor));
+}
+
+/*
+
+QPoint QXcbScreen::mapToNative(const QPoint &pos) const
+{
+    const int dpr = int(devicePixelRatio());
+    return (pos - m_geometry.topLeft()) * dpr + m_nativeGeometry.topLeft();
+}
+
+QPoint QXcbScreen::mapFromNative(const QPoint &pos) const
+{
+    const int dpr = int(devicePixelRatio());
+    return (pos - m_nativeGeometry.topLeft()) / dpr + m_geometry.topLeft();
+}
+
+
+ */
+
+
+QPoint QHighDpiScaling::mapPositionToNative(const QPoint &pos, const QPlatformScreen *platformScreen)
+{
+    if (!platformScreen)
+        return pos;
+    const qreal scaleFactor = factor(platformScreen);
+    const QPoint topLeft = platformScreen->geometry().topLeft();
+    return (pos - topLeft) * scaleFactor + topLeft;
+}
+
+QPoint QHighDpiScaling::mapPositionFromNative(const QPoint &pos, const QPlatformScreen *platformScreen)
+{
+    if (!platformScreen)
+        return pos;
+    const qreal scaleFactor = factor(platformScreen);
+    const QPoint topLeft = platformScreen->geometry().topLeft();
+    return (pos - topLeft) / scaleFactor + topLeft;
+}
+
+qreal QHighDpiScaling::screenSubfactor(const QPlatformScreen *screen)
+{
+    qreal factor = qreal(1.0);
+    if (m_perScreenActive && screen) {
+        if (m_usePixelDensity)
+            factor *= screen->pixelDensity();
+        QVariant screenFactor = screen->screen()->property(scaleFactorProperty);
+        if (screenFactor.isValid())
+            factor *= screenFactor.toReal();
+    }
+    return factor;
+}
+
+qreal QHighDpiScaling::factor(const QScreen *screen)
+{
+    // Fast path for when scaling in Qt is not used at all.
+    if (!m_active)
+        return qreal(1.0);
+
+    // The effective factor for a given screen is the product of the
+    // screen and global sub-factors
+    qreal factor = m_factor;
+    if (screen)
+        factor *= screenSubfactor(screen->handle());
+    return factor;
+}
+
+qreal QHighDpiScaling::factor(const QPlatformScreen *platformScreen)
+{
+    if (!m_active)
+        return qreal(1.0);
+
+    return m_factor * screenSubfactor(platformScreen);
+}
+
+qreal QHighDpiScaling::factor(const QWindow *window)
+{
+    if (!m_active || !window)
+        return qreal(1.0);
+
+    return factor(window->screen());
+}
+
+QPoint QHighDpiScaling::origin(const QScreen *screen)
+{
+    return screen->geometry().topLeft();
+}
+
+QPoint QHighDpiScaling::origin(const QPlatformScreen *platformScreen)
+{
+    return platformScreen->geometry().topLeft();
+}
+
+QT_END_NAMESPACE