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>

8 files changed, 715 insertions, 0 deletions

diff --git a/src/imports/imports.pro b/src/imports/imports.pro
index c49c05956d..20ade45fc8 100644
--- a/src/imports/imports.pro
+++ b/src/imports/imports.pro
@@ -15,6 +15,7 @@ qtHaveModule(quick) {
         layouts \
         qtquick2 \
         window \
+        sharedimage \
         testlib
 
     qtConfig(opengl(es1|es2)?): \
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"
diff --git a/src/imports/sharedimage/qmldir b/src/imports/sharedimage/qmldir
new file mode 100644
index 0000000000..64a5aa8ac1
--- /dev/null
+++ b/src/imports/sharedimage/qmldir
@@ -0,0 +1,3 @@
+module QtQuick.SharedImage
+plugin sharedimageplugin
+classname QtQuickSharedImagePlugin
diff --git a/src/imports/sharedimage/qsharedimageloader.cpp b/src/imports/sharedimage/qsharedimageloader.cpp
new file mode 100644
index 0000000000..65cbd92bb4
--- /dev/null
+++ b/src/imports/sharedimage/qsharedimageloader.cpp
@@ -0,0 +1,265 @@
+/****************************************************************************
+**
+** 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 "qsharedimageloader_p.h"
+#include <private/qobject_p.h>
+#include <private/qimage_p.h>
+#include <QSharedMemory>
+
+
+QT_BEGIN_NAMESPACE
+
+Q_LOGGING_CATEGORY(lcSharedImage, "qt.quick.sharedimage");
+
+struct SharedImageHeader {
+    quint8 magic;
+    quint8 version;
+    quint16 offset;
+    qint32 width;
+    qint32 height;
+    qint32 bpl;
+    QImage::Format format;
+};
+Q_STATIC_ASSERT(sizeof(SharedImageHeader) % 4 == 0);
+
+#ifndef QT_NO_SHAREDMEMORY
+struct SharedImageInfo {
+    QString path;
+    QPointer<QSharedMemory> shmp;
+};
+
+void cleanupSharedImage(void *cleanupInfo)
+{
+    if (!cleanupInfo)
+        return;
+    SharedImageInfo *sii = static_cast<SharedImageInfo *>(cleanupInfo);
+    qCDebug(lcSharedImage) << "Cleanup called for" << sii->path;
+    if (sii->shmp.isNull()) {
+        qCDebug(lcSharedImage) << "shm is 0 for" << sii->path;
+        return;
+    }
+    QSharedMemory *shm = sii->shmp.data();
+    sii->shmp.clear();
+    delete shm;    // destructor detaches
+    delete sii;
+}
+#else
+void cleanupSharedImage(void *) {}
+#endif
+
+class QSharedImageLoaderPrivate : public QObjectPrivate
+{
+    Q_DECLARE_PUBLIC(QSharedImageLoader)
+
+public:
+    QSharedImageLoaderPrivate()
+        : QObjectPrivate()
+    {}
+
+    QImage load(const QString &path, QSharedImageLoader::ImageParameters *params);
+
+    void storeImageToMem(void *data, const QImage &img);
+
+    bool verifyMem(const void *data, int size);
+
+    QImage createImageFromMem(const void *data, void *cleanupInfo);
+
+};
+
+
+void QSharedImageLoaderPrivate::storeImageToMem(void *data, const QImage &img)
+{
+    Q_ASSERT(data && !img.isNull());
+
+    SharedImageHeader *h = static_cast<SharedImageHeader *>(data);
+    h->magic = 'Q';
+    h->version = 1;
+    h->offset = sizeof(SharedImageHeader);
+    h->width = img.width();
+    h->height = img.height();
+    h->bpl = img.bytesPerLine();
+    h->format = img.format();
+
+    uchar *p = static_cast<uchar *>(data) + sizeof(SharedImageHeader);
+    memcpy(p, img.constBits(), img.byteCount());
+}
+
+
+bool QSharedImageLoaderPrivate::verifyMem(const void *data, int size)
+{
+    if (!data || size < int(sizeof(SharedImageHeader)))
+        return false;
+
+    const SharedImageHeader *h = static_cast<const SharedImageHeader *>(data);
+    if ((h->magic != 'Q')
+        || (h->version < 1)
+        || (h->offset < sizeof(SharedImageHeader))
+        || (h->width <= 0)
+        || (h->height <= 0)
+        || (h->bpl <= 0)
+        || (h->format <= QImage::Format_Invalid)
+        || (h->format >= QImage::NImageFormats)) {
+        return false;
+    }
+
+    int availSize = size - h->offset;
+    if (h->height * h->bpl > availSize)
+        return false;
+    if ((qt_depthForFormat(h->format) * h->width * h->height) > (8 * availSize))
+        return false;
+
+    return true;
+}
+
+
+QImage QSharedImageLoaderPrivate::createImageFromMem(const void *data, void *cleanupInfo)
+{
+    const SharedImageHeader *h = static_cast<const SharedImageHeader *>(data);
+    const uchar *p = static_cast<const uchar *>(data) + h->offset;
+
+    QImage img(p, h->width, h->height, h->bpl, h->format, cleanupSharedImage, cleanupInfo);
+    return img;
+}
+
+
+QImage QSharedImageLoaderPrivate::load(const QString &path, QSharedImageLoader::ImageParameters *params)
+{
+#ifndef QT_NO_SHAREDMEMORY
+    Q_Q(QSharedImageLoader);
+
+    QImage nil;
+    if (path.isEmpty())
+        return nil;
+
+    QScopedPointer<QSharedMemory> shm(new QSharedMemory(q->key(path, params)));
+    bool locked = false;
+
+    if (!shm->attach(QSharedMemory::ReadOnly)) {
+        QImage img = q->loadFile(path, params);
+        if (img.isNull())
+            return nil;
+        int size = sizeof(SharedImageHeader) + img.byteCount();
+        if (shm->create(size)) {
+            qCDebug(lcSharedImage) << "Created new shm segment of size" << size << "for image" << path;
+            if (!shm->lock()) {
+                qCDebug(lcSharedImage) << "Lock1 failed!?" << shm->errorString();
+                return nil;
+            }
+            locked = true;
+            storeImageToMem(shm->data(), img);
+        } else if (shm->error() == QSharedMemory::AlreadyExists) {
+            // race handling: other process may have created the share while
+            // we loaded the image, so try again to just attach
+            if (!shm->attach(QSharedMemory::ReadOnly)) {
+                qCDebug(lcSharedImage) << "Attach to existing failed?" << shm->errorString();
+                return nil;
+            }
+        } else {
+            qCDebug(lcSharedImage) << "Create failed?" << shm->errorString();
+            return nil;
+        }
+    }
+
+    Q_ASSERT(shm->isAttached());
+
+    if (!locked) {
+        if (!shm->lock()) {
+            qCDebug(lcSharedImage) << "Lock2 failed!?" << shm->errorString();
+            return nil;
+        }
+        locked = true;
+    }
+
+    if (!verifyMem(shm->constData(), shm->size())) {
+        qCDebug(lcSharedImage) << "Verifymem failed!?";
+        shm->unlock();
+        return nil;
+    }
+
+    QSharedMemory *shmp = shm.take();
+    SharedImageInfo *sii = new SharedImageInfo;
+    sii->path = path;
+    sii->shmp = shmp;
+    QImage shImg = createImageFromMem(shmp->constData(), sii);
+
+    if (!shmp->unlock()) {
+        qCDebug(lcSharedImage) << "UnLock failed!?";
+    }
+
+    return shImg;
+#else
+    Q_UNUSED(path);
+    Q_UNUSED(params);
+    return QImage();
+#endif
+}
+
+
+QSharedImageLoader::QSharedImageLoader(QObject *parent)
+    : QObject(*new QSharedImageLoaderPrivate, parent)
+{
+}
+
+QSharedImageLoader::~QSharedImageLoader()
+{
+}
+
+QImage QSharedImageLoader::load(const QString &path, ImageParameters *params)
+{
+    Q_D(QSharedImageLoader);
+
+    return d->load(path, params);
+}
+
+QImage QSharedImageLoader::loadFile(const QString &path, ImageParameters *params)
+{
+    Q_UNUSED(params);
+
+    return QImage(path);
+}
+
+QString QSharedImageLoader::key(const QString &path, ImageParameters *params)
+{
+    Q_UNUSED(params);
+
+    return path;
+}
+
+
+QT_END_NAMESPACE
diff --git a/src/imports/sharedimage/qsharedimageloader_p.h b/src/imports/sharedimage/qsharedimageloader_p.h
new file mode 100644
index 0000000000..afb50e5088
--- /dev/null
+++ b/src/imports/sharedimage/qsharedimageloader_p.h
@@ -0,0 +1,81 @@
+/****************************************************************************
+**
+** 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QSHAREDIMAGELOADER_H
+#define QSHAREDIMAGELOADER_H
+
+#include <QImage>
+#include <QVariant>
+#include <QLoggingCategory>
+
+QT_BEGIN_NAMESPACE
+
+Q_DECLARE_LOGGING_CATEGORY(lcSharedImage);
+
+class QSharedImageLoaderPrivate;
+
+class QSharedImageLoader : public QObject
+{
+    Q_OBJECT
+    Q_DECLARE_PRIVATE(QSharedImageLoader)
+
+public:
+    enum ImageParameter {
+        OriginalSize = 0,
+        RequestedSize,
+        NumImageParameters
+    };
+    typedef QVector<QVariant> ImageParameters;
+
+    QSharedImageLoader(QObject *parent = Q_NULLPTR);
+    ~QSharedImageLoader();
+
+    QImage load(const QString &path, ImageParameters *params = Q_NULLPTR);
+
+protected:
+    virtual QImage loadFile(const QString &path, ImageParameters *params);
+    virtual QString key(const QString &path, ImageParameters *params);
+
+private:
+    Q_DISABLE_COPY(QSharedImageLoader)
+};
+
+QT_END_NAMESPACE
+
+#endif // QSHAREDIMAGELOADER_H
diff --git a/src/imports/sharedimage/sharedimage.pro b/src/imports/sharedimage/sharedimage.pro
new file mode 100644
index 0000000000..523de66ac1
--- /dev/null
+++ b/src/imports/sharedimage/sharedimage.pro
@@ -0,0 +1,17 @@
+CXX_MODULE = qml
+TARGET = sharedimageplugin
+TARGETPATH = QtQuick/SharedImage
+IMPORT_VERSION = 1.0
+
+QT *= quick qml gui-private core-private
+
+SOURCES += \
+    plugin.cpp \
+    sharedimageprovider.cpp \
+    qsharedimageloader.cpp
+
+HEADERS += \
+    sharedimageprovider.h \
+    qsharedimageloader_p.h
+
+load(qml_plugin)
diff --git a/src/imports/sharedimage/sharedimageprovider.cpp b/src/imports/sharedimage/sharedimageprovider.cpp
new file mode 100644
index 0000000000..2dd3a130e9
--- /dev/null
+++ b/src/imports/sharedimage/sharedimageprovider.cpp
@@ -0,0 +1,156 @@
+/****************************************************************************
+**
+** 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 <sharedimageprovider.h>
+#include <qsharedimageloader_p.h>
+#include <qquickimageprovider.h>
+#include <private/qimage_p.h>
+#include <QImageReader>
+#include <QFileInfo>
+#include <QDir>
+
+class QuickSharedImageLoader : public QSharedImageLoader
+{
+    Q_OBJECT
+    friend class SharedImageProvider;
+
+public:
+    QuickSharedImageLoader(QObject *parent = Q_NULLPTR)
+        : QSharedImageLoader(parent)
+    {
+    }
+
+protected:
+    QImage loadFile(const QString &path, ImageParameters *params) override
+    {
+        QImageReader imgio(path);
+        QSize realSize = imgio.size();
+        QSize requestSize = params ? params->value(RequestedSize).toSize() : QSize();
+
+        // Following qquickpixmapcache's readImage, from here...
+        const bool force_scale = imgio.format() == "svg" || imgio.format() == "svgz";
+
+        if (requestSize.width() > 0 || requestSize.height() > 0) {
+            QSize s = realSize;
+            qreal ratio = 0.0;
+            if (requestSize.width() && (force_scale || requestSize.width() < s.width())) {
+                ratio = qreal(requestSize.width())/s.width();
+            }
+            if (requestSize.height() && (force_scale || requestSize.height() < s.height())) {
+                qreal hr = qreal(requestSize.height())/s.height();
+                if (ratio == 0.0 || hr < ratio)
+                    ratio = hr;
+            }
+            if (ratio > 0.0) {
+                s.setHeight(qRound(s.height() * ratio));
+                s.setWidth(qRound(s.width() * ratio));
+                imgio.setScaledSize(s);
+            }
+        }
+        // ... to here
+
+        QImage image;
+        if (imgio.read(&image)) {
+            if (realSize.isEmpty())
+                realSize = image.size();
+            // Make sure we have acceptable format for texture uploader, or it will convert & lose sharing
+            // This mimics the testing & conversion normally done by the quick pixmapcache & texturefactory
+            if (image.format() != QImage::Format_RGB32 && image.format() != QImage::Format_ARGB32_Premultiplied) {
+                QImage::Format newFmt = QImage::Format_RGB32;
+                if (image.hasAlphaChannel() && image.data_ptr()->checkForAlphaPixels())
+                    newFmt = QImage::Format_ARGB32_Premultiplied;
+                qCDebug(lcSharedImage) << "Convert on load from format" << image.format() << "to" << newFmt;
+                image = image.convertToFormat(newFmt);
+            }
+        }
+
+        if (params && params->count() > OriginalSize)
+            params->replace(OriginalSize, realSize);
+
+        return image;
+    }
+
+    QString key(const QString &path, ImageParameters *params) override
+    {
+        QSize reqSz = params->value(RequestedSize).toSize();
+        if (!reqSz.isValid())
+            return path;
+
+        QString key = path + QStringLiteral("_%1x%2").arg(reqSz.width()).arg(reqSz.height());
+        qCDebug(lcSharedImage) << "KEY:" << key;
+        return key;
+    }
+};
+
+
+SharedImageProvider::SharedImageProvider()
+    : QQuickImageProvider(QQuickImageProvider::Image), loader(new QuickSharedImageLoader)
+{
+}
+
+QImage SharedImageProvider::requestImage(const QString &id, QSize *size, const QSize &requestedSize)
+{
+    QFileInfo fi(QDir::root(), id);
+    QString path = fi.canonicalFilePath();
+    if (path.isEmpty())
+        return QImage();
+
+    QSharedImageLoader::ImageParameters params(QSharedImageLoader::NumImageParameters);
+    params[QSharedImageLoader::RequestedSize].setValue(requestedSize);
+
+    QImage img = loader->load(path, &params);
+    if (img.isNull()) {
+        // May be sharing problem, fall back to normal local load
+        img = loader->loadFile(path, &params);
+        if (!img.isNull())
+            qCWarning(lcSharedImage) << "Sharing problem; loading" << id << "unshared";
+    }
+
+    //... QSize realSize = params.value(QSharedImageLoader::OriginalSize).toSize();
+    // quickpixmapcache's readImage() reports back the original size, prior to requestedSize scaling, in the *size
+    // parameter. That value is currently ignored by quick however, which only cares about the present size of the
+    // returned image. So handling and sharing of info on pre-scaled size is currently not implemented.
+    if (size) {
+        *size = img.size();
+    }
+
+    return img;
+}
+
+#include "sharedimageprovider.moc"
diff --git a/src/imports/sharedimage/sharedimageprovider.h b/src/imports/sharedimage/sharedimageprovider.h
new file mode 100644
index 0000000000..a2f6b6ef2f
--- /dev/null
+++ b/src/imports/sharedimage/sharedimageprovider.h
@@ -0,0 +1,58 @@
+/****************************************************************************
+**
+** 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef SHAREDIMAGEPROVIDER_H
+#define SHAREDIMAGEPROVIDER_H
+
+#include <QQuickImageProvider>
+#include <QScopedPointer>
+
+class QuickSharedImageLoader;
+
+class SharedImageProvider : public QQuickImageProvider
+{
+public:
+    SharedImageProvider();
+
+    QImage requestImage(const QString &id, QSize *size, const QSize &requestedSize) override;
+
+protected:
+    QScopedPointer<QuickSharedImageLoader> loader;
+};
+#endif // SHAREDIMAGEPROVIDER_H