Make it possible to have built-in adaptations

In addition to QMLSCENE_DEVICE, start supporting an env var named
QT_QUICK_BACKEND. This is more suitable for general use.

Besides plugin-based adaptations, some built-in ones are anticipated as
well. Therefore, add support for shipping custom contexts as part of the
scenegraph. For test purposes, a dummy adaptation is provided that falls
back to the default, OpenGL-based path for everything. This may
be removed at some point later on, but is useful for testing the loading
logic for now.

Change-Id: I7e0a2cd3ef33ba910604fb4027af3b3711fcaf1e
Reviewed-by: Andy Nichols <andy.nichols@theqtcompany.com>

6 files changed, 248 insertions, 47 deletions

diff --git a/src/quick/scenegraph/adaptations/adaptations.pri b/src/quick/scenegraph/adaptations/adaptations.pri
new file mode 100644
index 0000000000..3511971cac
--- /dev/null
+++ b/src/quick/scenegraph/adaptations/adaptations.pri
@@ -0,0 +1 @@
+include(dummy/dummy.pri)
diff --git a/src/quick/scenegraph/adaptations/dummy/dummy.pri b/src/quick/scenegraph/adaptations/dummy/dummy.pri
new file mode 100644
index 0000000000..f81655dcaa
--- /dev/null
+++ b/src/quick/scenegraph/adaptations/dummy/dummy.pri
@@ -0,0 +1,5 @@
+SOURCES += \
+    $$PWD/qsgdummyadaptation.cpp
+
+HEADERS += \
+    $$PWD/qsgdummyadaptation_p.h
diff --git a/src/quick/scenegraph/adaptations/dummy/qsgdummyadaptation.cpp b/src/quick/scenegraph/adaptations/dummy/qsgdummyadaptation.cpp
new file mode 100644
index 0000000000..98f6872533
--- /dev/null
+++ b/src/quick/scenegraph/adaptations/dummy/qsgdummyadaptation.cpp
@@ -0,0 +1,90 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** 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 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 "qsgdummyadaptation_p.h"
+
+#include <private/qguiapplication_p.h>
+#include <qpa/qplatformintegration.h>
+
+QT_BEGIN_NAMESPACE
+
+class QSGDummyContext : public QSGContext
+{
+public:
+    QSGDummyContext(QObject *parent = 0) : QSGContext(parent) { }
+
+    QSGRenderContext *createRenderContext() override { return QSGContext::createRenderContext(); }
+    QSGRectangleNode *createRectangleNode() override { return QSGContext::createRectangleNode(); }
+    QSGImageNode *createImageNode() override { return QSGContext::createImageNode(); }
+    QSGPainterNode *createPainterNode(QQuickPaintedItem *item) override { return QSGContext::createPainterNode(item); }
+    QSGGlyphNode *createGlyphNode(QSGRenderContext *rc, bool preferNativeGlyphNode) override  { return QSGContext::createGlyphNode(rc, preferNativeGlyphNode); }
+    QSGNinePatchNode *createNinePatchNode() override { return QSGContext::createNinePatchNode(); }
+    QSGLayer *createLayer(QSGRenderContext *rc) override { return QSGContext::createLayer(rc); }
+    QSurfaceFormat defaultSurfaceFormat() const override { return QSGContext::defaultSurfaceFormat(); }
+};
+
+QSGDummyAdaptation::QSGDummyAdaptation(QObject *parent)
+    : QSGContextPlugin(parent)
+{
+}
+
+QStringList QSGDummyAdaptation::keys() const
+{
+    return QStringList() << QLatin1String("dummy");
+}
+
+QSGContext *QSGDummyAdaptation::create(const QString &) const
+{
+    if (!contextInstance) {
+        qDebug("Creating OpenGL SG context via dummy");
+        contextInstance = new QSGDummyContext;
+    }
+
+    return contextInstance;
+}
+
+QSGRenderLoop *QSGDummyAdaptation::createWindowManager()
+{
+    qDebug("Creating default OpenGL render loop via dummy");
+    return nullptr;
+}
+
+QSGDummyContext *QSGDummyAdaptation::contextInstance = nullptr;
+
+QT_END_NAMESPACE
diff --git a/src/quick/scenegraph/adaptations/dummy/qsgdummyadaptation_p.h b/src/quick/scenegraph/adaptations/dummy/qsgdummyadaptation_p.h
new file mode 100644
index 0000000000..aa0599de79
--- /dev/null
+++ b/src/quick/scenegraph/adaptations/dummy/qsgdummyadaptation_p.h
@@ -0,0 +1,76 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** 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 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 QSGDUMMYADAPTATION_P_H
+#define QSGDUMMYADAPTATION_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <private/qsgcontext_p.h>
+#include <private/qsgcontextplugin_p.h>
+
+QT_BEGIN_NAMESPACE
+
+class QSGDummyContext;
+
+class QSGDummyAdaptation : public QSGContextPlugin
+{
+public:
+    QSGDummyAdaptation(QObject *parent = 0);
+
+    QStringList keys() const override;
+    QSGContext *create(const QString &key) const override;
+    QSGRenderLoop *createWindowManager() override;
+
+private:
+    static QSGDummyContext *contextInstance;
+};
+
+QT_END_NAMESPACE
+
+#endif // QSGDUMMYADAPTATION_P_H
diff --git a/src/quick/scenegraph/qsgcontextplugin.cpp b/src/quick/scenegraph/qsgcontextplugin.cpp
index f5c2b6880b..bc5d2a0a0d 100644
--- a/src/quick/scenegraph/qsgcontextplugin.cpp
+++ b/src/quick/scenegraph/qsgcontextplugin.cpp
@@ -43,8 +43,13 @@
 #include <QtCore/private/qfactoryloader_p.h>
 #include <QtCore/qlibraryinfo.h>
 
+// Built-in adaptations
+#include <QtQuick/private/qsgdummyadaptation_p.h>
+
 QT_BEGIN_NAMESPACE
 
+Q_DECLARE_LOGGING_CATEGORY(QSG_LOG_INFO)
+
 QSGContextPlugin::QSGContextPlugin(QObject *parent)
     : QObject(parent)
 {
@@ -59,61 +64,86 @@ Q_GLOBAL_STATIC_WITH_ARGS(QFactoryLoader, loader,
     (QSGContextFactoryInterface_iid, QLatin1String("/scenegraph")))
 #endif
 
-struct QSGAdaptionPluginData
+struct QSGAdaptionBackendData
 {
-    QSGAdaptionPluginData()
-        : tried(false)
-        , factory(0)
-    {
-    }
-
-    ~QSGAdaptionPluginData()
-    {
-    }
+    QSGAdaptionBackendData();
 
     bool tried;
     QSGContextFactoryInterface *factory;
-    QString deviceName;
+    QString name;
+
+    QVector<QSGContextFactoryInterface *> builtIns;
 };
 
-Q_GLOBAL_STATIC(QSGAdaptionPluginData, qsg_adaptation_data)
+QSGAdaptionBackendData::QSGAdaptionBackendData()
+    : tried(false)
+    , factory(0)
+{
+    // Fill in the table with the built-in adaptations.
+    builtIns.append(new QSGDummyAdaptation);
+}
+
+Q_GLOBAL_STATIC(QSGAdaptionBackendData, qsg_adaptation_data)
 
-QSGAdaptionPluginData *contextFactory()
+QSGAdaptionBackendData *contextFactory()
 {
-    QSGAdaptionPluginData *plugin = qsg_adaptation_data();
-    if (!plugin->tried) {
+    QSGAdaptionBackendData *backendData = qsg_adaptation_data();
+
+    if (!backendData->tried) {
+        backendData->tried = true;
 
-        plugin->tried = true;
         const QStringList args = QGuiApplication::arguments();
-        QString device;
+        QString requestedBackend;
         for (int index = 0; index < args.count(); ++index) {
             if (args.at(index).startsWith(QLatin1String("--device="))) {
-                device = args.at(index).mid(9);
+                requestedBackend = args.at(index).mid(9);
                 break;
             }
         }
-        if (device.isEmpty())
-            device = QString::fromLocal8Bit(qgetenv("QMLSCENE_DEVICE"));
 
-#ifndef QT_NO_LIBRARY
-        if (!device.isEmpty()) {
-            const int index = loader()->indexOf(device);
-            if (index != -1)
-                plugin->factory = qobject_cast<QSGContextFactoryInterface*>(loader()->instance(index));
-            plugin->deviceName = device;
+        if (requestedBackend.isEmpty() && qEnvironmentVariableIsSet("QMLSCENE_DEVICE"))
+            requestedBackend = QString::fromLocal8Bit(qgetenv("QMLSCENE_DEVICE"));
+
+        // A modern alternative. Scenegraph adaptations can represent backends
+        // for different graphics APIs as well, instead of being specific to
+        // some device or platform.
+        if (requestedBackend.isEmpty() && qEnvironmentVariableIsSet("QT_QUICK_BACKEND"))
+            requestedBackend = QString::fromLocal8Bit(qgetenv("QT_QUICK_BACKEND"));
+
+        if (!requestedBackend.isEmpty()) {
 #ifndef QT_NO_DEBUG
-            if (!plugin->factory) {
-                qWarning("Could not create scene graph context for device '%s'"
-                         " - check that plugins are installed correctly in %s",
-                         qPrintable(device),
-                         qPrintable(QLibraryInfo::location(QLibraryInfo::PluginsPath)));
-            }
+            qCDebug(QSG_LOG_INFO) << "Loading backend" << requestedBackend;
 #endif
-        }
 
+            // First look for a built-in adaptation.
+            for (QSGContextFactoryInterface *builtInBackend : qAsConst(backendData->builtIns)) {
+                if (builtInBackend->keys().contains(requestedBackend)) {
+                    backendData->factory = builtInBackend;
+                    break;
+                }
+            }
+
+            // Then try the plugins.
+            if (!backendData->factory) {
+#ifndef QT_NO_LIBRARY
+                const int index = loader()->indexOf(requestedBackend);
+                if (index != -1)
+                    backendData->factory = qobject_cast<QSGContextFactoryInterface*>(loader()->instance(index));
+                backendData->name = requestedBackend;
+#ifndef QT_NO_DEBUG
+                if (!backendData->factory) {
+                    qWarning("Could not create scene graph context for backend '%s'"
+                             " - check that plugins are installed correctly in %s",
+                             qPrintable(requestedBackend),
+                             qPrintable(QLibraryInfo::location(QLibraryInfo::PluginsPath)));
+                }
+#endif
+            }
 #endif // QT_NO_LIBRARY
+        }
     }
-    return plugin;
+
+    return backendData;
 }
 
 
@@ -126,9 +156,9 @@ QSGAdaptionPluginData *contextFactory()
 */
 QSGContext *QSGContext::createDefaultContext()
 {
-    QSGAdaptionPluginData *plugin = contextFactory();
-    if (plugin->factory)
-        return plugin->factory->create(plugin->deviceName);
+    QSGAdaptionBackendData *backendData = contextFactory();
+    if (backendData->factory)
+        return backendData->factory->create(backendData->name);
     return new QSGContext();
 }
 
@@ -143,9 +173,9 @@ QSGContext *QSGContext::createDefaultContext()
 
 QQuickTextureFactory *QSGContext::createTextureFactoryFromImage(const QImage &image)
 {
-    QSGAdaptionPluginData *plugin = contextFactory();
-    if (plugin->factory)
-        return plugin->factory->createTextureFactoryFromImage(image);
+    QSGAdaptionBackendData *backendData = contextFactory();
+    if (backendData->factory)
+        return backendData->factory->createTextureFactoryFromImage(image);
     return 0;
 }
 
@@ -157,14 +187,10 @@ QQuickTextureFactory *QSGContext::createTextureFactoryFromImage(const QImage &im
 
 QSGRenderLoop *QSGContext::createWindowManager()
 {
-    QSGAdaptionPluginData *plugin = contextFactory();
-    if (plugin->factory)
-        return plugin->factory->createWindowManager();
+    QSGAdaptionBackendData *backendData = contextFactory();
+    if (backendData->factory)
+        return backendData->factory->createWindowManager();
     return 0;
 }
 
-
-
-
-
 QT_END_NAMESPACE
diff --git a/src/quick/scenegraph/scenegraph.pri b/src/quick/scenegraph/scenegraph.pri
index 84cc2ba135..33f6dff8cf 100644
--- a/src/quick/scenegraph/scenegraph.pri
+++ b/src/quick/scenegraph/scenegraph.pri
@@ -100,6 +100,9 @@ SOURCES += \
     $$PWD/qsgwindowsrenderloop.cpp \
     $$PWD/qsgdefaultlayer.cpp
 
+# Built-in, non-plugin-based adaptations
+include(adaptations/adaptations.pri)
+
 RESOURCES += \
     $$PWD/scenegraph.qrc