Add devicePixelRatio support to the Windows QPA plugin.

This adds support for the environment variable
QT_DEVICE_PIXEL_RATIO for the Windows platform plugin.

Task-number: QTBUG-38993
Task-number: QTBUG-38858
Change-Id: I6831eb6d3a09a80be7bbef46395e91531b61cc50
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>

1 files changed, 79 insertions, 0 deletions

diff --git a/src/plugins/platforms/windows/qwindowsscaling.cpp b/src/plugins/platforms/windows/qwindowsscaling.cpp
new file mode 100644
index 0000000000..fcc3440b42
--- /dev/null
+++ b/src/plugins/platforms/windows/qwindowsscaling.cpp
@@ -0,0 +1,79 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the plugins 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
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+** 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.
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+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include  "qwindowsscaling.h"
+#include  "qwindowsscreen.h"
+
+#include <QtCore/QDebug>
+#include <QtCore/QCoreApplication>
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \class QWindowsScaling
+    \brief Windows scaling utilities
+
+    \internal
+    \ingroup qt-lighthouse-win
+*/
+
+int QWindowsScaling::m_factor = 1;
+
+static const char devicePixelRatioEnvVar[] = "QT_DEVICE_PIXEL_RATIO";
+
+// Suggest a scale factor by checking monitor sizes.
+int QWindowsScaling::determineUiScaleFactor()
+{
+    if (!qEnvironmentVariableIsSet(devicePixelRatioEnvVar))
+        return 1;
+    const QByteArray envDevicePixelRatioEnv = qgetenv(devicePixelRatioEnvVar);
+    // Auto: Suggest a scale factor by checking monitor resolution.
+    if (envDevicePixelRatioEnv == QByteArrayLiteral("auto")) {
+        const int maxResolution = QWindowsScreen::maxMonitorHorizResolution();
+        return maxResolution > 180 ? maxResolution / 96 : 1;
+    }
+    // Get factor from environment
+    bool ok = false;
+    const int envFactor = envDevicePixelRatioEnv.toInt(&ok);
+    return ok && envFactor > 0 ? envFactor : 1;
+}
+
+QT_END_NAMESPACE