Expose the scene graph publically through a QSGEngine class

This change wraps QSGRenderContext and QSGContext in a new QSGEngine
class, and expose a public interface of QSGRenderer through a
QSGAbstractRenderer to make it usable on a standalone window or FBO.

Change-Id: I2d41187472424f5ea64650a006bcd61f2711f6b9
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>

3 files changed, 350 insertions, 0 deletions

diff --git a/src/quick/scenegraph/util/qsgengine.cpp b/src/quick/scenegraph/util/qsgengine.cpp
new file mode 100644
index 0000000000..127f624d8b
--- /dev/null
+++ b/src/quick/scenegraph/util/qsgengine.cpp
@@ -0,0 +1,204 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtQuick 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 "qsgengine_p.h"
+
+#include <QtQuick/qsgtexture.h>
+#include <private/qsgcontext_p.h>
+#include <private/qsgrenderer_p.h>
+#include <private/qsgtexture_p.h>
+
+QT_BEGIN_NAMESPACE
+
+
+/*!
+    \class QSGEngine
+    \brief The QSGEngine class allows low level rendering of a scene graph.
+    \inmodule QtQuick
+    \since 5.4
+
+    A QSGEngine can be used to render a tree of QSGNode directly on a QWindow
+    or QOpenGLFramebufferObject without any integration with QML, QQuickWindow
+    or QQuickItem and the convenience that they provide.
+
+    This means that you must handle event propagation, animation timing,
+    and node lifetime yourself.
+
+    \note This class is for very low level access to an independent scene graph.
+    Most of the time you will instead want to subclass QQuickItem and insert
+    your QSGNode in a normal QtQuick scene by overriding QQuickItem::updatePaintNode().
+
+    \sa QSGAbstractRenderer
+ */
+
+/*!
+    \enum QSGEngine::CreateTextureOption
+
+    The CreateTextureOption enums are used to customize how a texture is wrapped.
+
+    \value TextureHasAlphaChannel The texture has an alpha channel and should
+    be drawn using blending.
+
+    \value TextureOwnsGLTexture The texture object owns the texture id and
+    will delete the GL texture when the texture object is deleted.
+
+    \value TextureCanUseAtlas The image can be uploaded into a texture atlas.
+ */
+
+QSGEnginePrivate::QSGEnginePrivate()
+    : sgContext(QSGContext::createDefaultContext())
+    , sgRenderContext(new QSGRenderContext(sgContext.data()))
+{
+}
+
+/*!
+    Constructs a new QSGEngine with its \a parent
+ */
+QSGEngine::QSGEngine(QObject *parent)
+    : QObject(*(new QSGEnginePrivate), parent)
+{
+}
+
+/*!
+    Destroys the engine
+ */
+QSGEngine::~QSGEngine()
+{
+}
+
+/*!
+    Initialize the engine with \a context.
+
+    \warning You have to make sure that you call
+    QOpenGLContext::makeCurrent() on \a context before calling this.
+ */
+void QSGEngine::initialize(QOpenGLContext *context)
+{
+    Q_D(QSGEngine);
+    if (QOpenGLContext::currentContext() != context) {
+        qWarning("WARNING: The context must be current before calling QSGEngine::initialize.");
+        return;
+    }
+
+    if (!d->sgRenderContext->isValid()) {
+        d->sgRenderContext->setAttachToGLContext(false);
+        d->sgRenderContext->initialize(context);
+        connect(context, &QOpenGLContext::aboutToBeDestroyed, this, &QSGEngine::invalidate);
+    }
+}
+
+/*!
+    Invalidate the engine releasing its resources
+
+    You will have to call initialize() and createRenderer() if you
+    want to use it again.
+ */
+void QSGEngine::invalidate()
+{
+    Q_D(QSGEngine);
+    d->sgRenderContext->invalidate();
+}
+
+/*!
+    Returns a renderer that can be used to render a QSGNode tree
+
+    You call initialize() first with the QOpenGLContext that you
+    want to use with this renderer. This will return a null
+    renderer otherwise.
+ */
+QSGAbstractRenderer *QSGEngine::createRenderer() const
+{
+    Q_D(const QSGEngine);
+    if (!d->sgRenderContext->isValid())
+        return 0;
+
+    QSGRenderer *renderer = d->sgRenderContext->createRenderer();
+    renderer->setCustomRenderMode(qgetenv("QSG_VISUALIZE"));
+    return renderer;
+}
+
+/*!
+    Creates a texture using the data of \a image
+
+    Valid \a options are TextureCanUseAtlas
+
+    The caller takes ownership of the texture and the
+    texture should only be used with this engine.
+
+    \sa createTextureFromId(), QSGSimpleTextureNode::setOwnsTexture(), QQuickWindow::createTextureFromImage()
+ */
+QSGTexture *QSGEngine::createTextureFromImage(const QImage &image, CreateTextureOptions options) const
+{
+    Q_D(const QSGEngine);
+    if (!d->sgRenderContext->isValid())
+        return 0;
+
+    if (options & TextureCanUseAtlas)
+        return d->sgRenderContext->createTexture(image);
+    else
+        return d->sgRenderContext->createTextureNoAtlas(image);
+}
+
+/*!
+    Creates a texture object that wraps the GL texture \a id uploaded with \a size
+
+    Valid \a options are TextureHasAlphaChannel and TextureOwnsGLTexture
+
+    The caller takes ownership of the texture object and the
+    texture should only be used with this engine.
+
+    \sa createTextureFromImage(), QSGSimpleTextureNode::setOwnsTexture(), QQuickWindow::createTextureFromId()
+ */
+QSGTexture *QSGEngine::createTextureFromId(uint id, const QSize &size, CreateTextureOptions options) const
+{
+    Q_D(const QSGEngine);
+    if (d->sgRenderContext->isValid()) {
+        QSGPlainTexture *texture = new QSGPlainTexture();
+        texture->setTextureId(id);
+        texture->setHasAlphaChannel(options & TextureHasAlphaChannel);
+        texture->setOwnsTexture(options & TextureOwnsGLTexture);
+        texture->setTextureSize(size);
+        return texture;
+    }
+    return 0;
+}
+
+QT_END_NAMESPACE
diff --git a/src/quick/scenegraph/util/qsgengine.h b/src/quick/scenegraph/util/qsgengine.h
new file mode 100644
index 0000000000..7aae882a70
--- /dev/null
+++ b/src/quick/scenegraph/util/qsgengine.h
@@ -0,0 +1,80 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtQuick 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.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QSGENGINE_H
+#define QSGENGINE_H
+
+#include <QtCore/QObject>
+#include <QtQuick/qtquickglobal.h>
+
+QT_BEGIN_NAMESPACE
+
+class QOpenGLContext;
+class QSGAbstractRenderer;
+class QSGEnginePrivate;
+class QSGTexture;
+
+class Q_QUICK_EXPORT QSGEngine : public QObject
+{
+    Q_OBJECT
+    Q_DECLARE_PRIVATE(QSGEngine)
+public:
+    enum CreateTextureOption {
+        TextureHasAlphaChannel  = 0x0001,
+        TextureOwnsGLTexture    = 0x0004,
+        TextureCanUseAtlas      = 0x0008
+    };
+    Q_DECLARE_FLAGS(CreateTextureOptions, CreateTextureOption)
+
+    QSGEngine(QObject *parent = 0);
+    ~QSGEngine();
+
+    void initialize(QOpenGLContext *context);
+    void invalidate();
+
+    QSGAbstractRenderer *createRenderer() const;
+    QSGTexture *createTextureFromImage(const QImage &image, CreateTextureOptions options = CreateTextureOption(0)) const;
+    QSGTexture *createTextureFromId(uint id, const QSize &size, CreateTextureOptions options = CreateTextureOption(0)) const;
+};
+
+QT_END_NAMESPACE
+
+#endif // QSGENGINE_H
diff --git a/src/quick/scenegraph/util/qsgengine_p.h b/src/quick/scenegraph/util/qsgengine_p.h
new file mode 100644
index 0000000000..a7e1599fd5
--- /dev/null
+++ b/src/quick/scenegraph/util/qsgengine_p.h
@@ -0,0 +1,66 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtQuick 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.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QSGENGINE_P_H
+#define QSGENGINE_P_H
+
+#include "qsgengine.h"
+#include <private/qobject_p.h>
+
+QT_BEGIN_NAMESPACE
+
+class QSGContext;
+class QSGRenderContext;
+
+class QSGEnginePrivate : public QObjectPrivate
+{
+    Q_DECLARE_PUBLIC(QSGEngine)
+
+public:
+    QSGEnginePrivate();
+
+    QScopedPointer<QSGContext> sgContext;
+    QScopedPointer<QSGRenderContext> sgRenderContext;
+};
+
+QT_END_NAMESPACE
+
+#endif // QSGENGINE_P_H