Renderer: Add CommandThread class to perform GL operations in a secondary thread

Change-Id: Ida3e6a6ad47d5a8f7a262dc8e6a42f240bf146d5
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

3 files changed, 238 insertions, 2 deletions

diff --git a/src/render/backend/commandthread.cpp b/src/render/backend/commandthread.cpp
new file mode 100644
index 000000000..f91cff017
--- /dev/null
+++ b/src/render/backend/commandthread.cpp
@@ -0,0 +1,129 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 Klaralvdalens Datakonsult AB (KDAB).
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt3D 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 "commandthread_p.h"
+#include <QOpenGLContext>
+
+QT_BEGIN_NAMESPACE
+
+namespace Qt3DRender {
+
+namespace Render {
+
+CommandThread::CommandThread(Renderer *renderer)
+    : QThread()
+    , m_renderer(renderer)
+    , m_waitForStartSemaphore(0)
+    , m_initializedSemaphore(0)
+{
+}
+
+CommandThread::~CommandThread()
+{
+}
+
+// Called by RenderThread or MainThread (Scene3d)
+void CommandThread::initialize(QOpenGLContext *mainContext)
+{
+    // Start the thread
+    start();
+
+    // Wait for thread to be started
+    m_waitForStartSemaphore.acquire();
+
+    m_mainContext = mainContext;
+    Q_ASSERT(m_mainContext);
+
+    // Allow thread to proceed
+    m_initializedSemaphore.release();
+}
+
+// Called by RenderThread of MainThread (Scene3D)
+void CommandThread::shutdown()
+{
+    // Tell thread to exit event loop
+    QThread::quit();
+
+    // Wait for thread to exit
+    wait();
+
+    // Reset semaphores (in case we ever want to restart)
+    m_waitForStartSemaphore.release(m_waitForStartSemaphore.available());
+    m_initializedSemaphore.release(m_initializedSemaphore.available());
+    m_localContext.reset();
+}
+
+// Any thread can call this, this is a blocking command
+void CommandThread::executeCommand(Command *command)
+{
+    if (!isRunning())
+        return;
+    QMetaObject::invokeMethod(this,
+                              "executeCommandInternal",
+                              Qt::BlockingQueuedConnection,
+                              Q_ARG(Command *, command));
+}
+
+void CommandThread::run()
+{
+    // Allow initialize to proceed
+    m_waitForStartSemaphore.release();
+
+    // Wait for initialize to be completed
+    m_initializedSemaphore.acquire();
+
+    // Initialize shared context and resources for the thread
+    m_localContext.reset(new QOpenGLContext());
+    m_localContext->setShareContext(m_mainContext);
+
+    // Launch exec loop
+    QThread::exec();
+}
+
+// Executed in the Command Thread
+void CommandThread::executeCommandInternal(Command *command)
+{
+    command->execute(m_renderer, m_localContext.data());
+}
+
+} // Render
+
+} // Qt3DRender
+
+QT_END_NAMESPACE
diff --git a/src/render/backend/commandthread_p.h b/src/render/backend/commandthread_p.h
new file mode 100644
index 000000000..1955d13ac
--- /dev/null
+++ b/src/render/backend/commandthread_p.h
@@ -0,0 +1,105 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 Klaralvdalens Datakonsult AB (KDAB).
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt3D 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 QT3DRENDER_RENDER_COMMANDTHREAD_P_H
+#define QT3DRENDER_RENDER_COMMANDTHREAD_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists for the convenience
+// of other Qt classes.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/QThread>
+#include <QtCore/QSemaphore>
+
+QT_BEGIN_NAMESPACE
+
+class QOpenGLContext;
+
+namespace Qt3DRender {
+
+namespace Render {
+
+class Renderer;
+
+class Command
+{
+public:
+    virtual void execute(Renderer *renderer, QOpenGLContext *localContext) = 0;
+};
+
+class CommandThread : public QThread
+{
+    Q_OBJECT
+public:
+    explicit CommandThread(Renderer *renderer);
+    ~CommandThread();
+
+    Render::Renderer* renderer() const { return m_renderer; }
+
+    void initialize(QOpenGLContext *mainContext);
+    void shutdown();
+
+    void executeCommand(Command *command);
+
+private:
+    void run() Q_DECL_OVERRIDE;
+    Q_INVOKABLE void executeCommandInternal(Command *command);
+
+private:
+    Renderer* m_renderer;
+    QSemaphore m_waitForStartSemaphore;
+    QSemaphore m_initializedSemaphore;
+    QOpenGLContext *m_mainContext;
+    QScopedPointer<QOpenGLContext> m_localContext;
+};
+
+} // Render
+
+} // Qt3DRender
+
+QT_END_NAMESPACE
+
+#endif // QT3DRENDER_RENDER_COMMANDTHREAD_P_H
diff --git a/src/render/backend/render-backend.pri b/src/render/backend/render-backend.pri
index 14e9c6370..a7f312eab 100644
--- a/src/render/backend/render-backend.pri
+++ b/src/render/backend/render-backend.pri
@@ -44,7 +44,8 @@ HEADERS += \
     $$PWD/renderviewbuilder_p.h \
     $$PWD/frameprofiler_p.h \
     $$PWD/offscreensurfacehelper_p.h \
-    $$PWD/resourceaccessor_p.h
+    $$PWD/resourceaccessor_p.h \
+    $$PWD/commandthread_p.h
 
 SOURCES += \
     $$PWD/renderthread.cpp \
@@ -79,5 +80,6 @@ SOURCES += \
     $$PWD/shaderparameterpack.cpp \
     $$PWD/renderviewbuilder.cpp \
     $$PWD/offscreensurfacehelper.cpp \
-    $$PWD/resourceaccessor.cpp
+    $$PWD/resourceaccessor.cpp \
+    $$PWD/commandthread.cpp