Add shared memory image provider

Adds functionality to save CPU memory when several processes use the
same local image files.

Example and autotest will be added during stabilization.

Task-number: QTBUG-56279
Change-Id: Iabe1e42620c79adca4f61f3901da41d9d5a723df
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

1 files changed, 134 insertions, 0 deletions

diff --git a/src/imports/sharedimage/plugin.cpp b/src/imports/sharedimage/plugin.cpp
new file mode 100644
index 0000000000..f20edc641c
--- /dev/null
+++ b/src/imports/sharedimage/plugin.cpp
@@ -0,0 +1,134 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** 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
+** 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 <qqmlextensionplugin.h>
+#include <qqmlengine.h>
+#include <sharedimageprovider.h>
+
+
+/*!
+    \qmlmodule QtQuick.SharedImage 1
+    \title Qt Quick Shared Image Provider
+    \ingroup qmlmodules
+    \brief Adds an image provider which utilizes shared CPU memory
+
+    \section2 Summary
+
+    This module provides functionality to save memory in use cases where
+    several Qt Quick applications use the same local image files. It does this
+    by placing the decoded QImage data in shared system memory, making it
+    accessible to all the processes (see QSharedMemory).
+
+    This module only shares CPU memory. It does not provide sharing of GPU
+    memory or textures.
+
+    \section2 Usage
+
+    To use this module, import it like this:
+    \code
+    import QtQuick.SharedImage 1.0
+    \endcode
+
+    The sharing functionality is provided through a QQuickImageProvider. Use
+    the "image:" scheme for the URL source of the image, followed by the
+    identifier \e shared, followed by the image file path. For example:
+
+    \code
+    Image { source: "image://shared/usr/share/wallpapers/mybackground.jpg" }
+    \endcode
+
+    This will look for the file \e /usr/share/wallpapers/mybackground.jpg.
+    The first process that does this will read the image file
+    using normal Qt image loading. The decoded image data will then be placed
+    in shared memory, using the full file path as key. Later processes
+    requesting the same image will discover that the data is already available
+    in shared memory. They will then use that instead of loading the image file
+    again.
+
+    The shared image data will be kept available until the last process has deleted
+    its last reference to the shared image, at which point it is automatically released.
+
+    If system memory sharing is not available, the shared image provider falls
+    back to normal, unshared image loading.
+
+    The file path must be absolute. To use a relative path, make it absolute
+    using \e Qt.resolvedUrl() and replace the URL scheme. For example:
+
+    \code
+    ...
+    property string imagePrefix: Qt.resolvedUrl("../myimages/").replace("file://", "image://shared/")
+    Image { source: imagePrefix + "myimage.png" }
+    \endcode
+
+    The shared image module does not provide any directly usable QML types.
+*/
+
+static void initResources()
+{
+#ifdef QT_STATIC
+    Q_INIT_RESOURCE(qmake_QtQuick_SharedImage);
+#endif
+}
+
+QT_BEGIN_NAMESPACE
+
+class QtQuickSharedImagePlugin : public QQmlExtensionPlugin
+{
+    Q_OBJECT
+    Q_PLUGIN_METADATA(IID QQmlExtensionInterface_iid)
+public:
+    QtQuickSharedImagePlugin(QObject *parent = 0) : QQmlExtensionPlugin(parent) { initResources(); }
+
+    void registerTypes(const char *uri) Q_DECL_OVERRIDE
+    {
+        Q_ASSERT(uri == QStringLiteral("QtQuick.SharedImage"));
+        // Need to register *something* to let our version number be known:
+        qmlRegisterTypeNotAvailable(uri, 1, 0, "nosuchtype", QStringLiteral("Just a dummy type, do not use"));
+    }
+
+    void initializeEngine(QQmlEngine *engine, const char *uri) override
+    {
+        Q_UNUSED(uri);
+        engine->addImageProvider("shared", new SharedImageProvider);
+    }
+};
+
+QT_END_NAMESPACE
+
+#include "plugin.moc"