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** Copyright (C) 2016 Klaralvdalens Datakonsult AB (KDAB).
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#include "scene3drenderer_p.h"

#include <Qt3DCore/qaspectengine.h>
#include <Qt3DRender/qrenderaspect.h>
#include <QtCore/qthread.h>
#include <qopenglcontext.h>
#include <qopenglframebufferobject.h>
#include <QtQuick/qquickwindow.h>

#include <Qt3DRender/private/qrenderaspect_p.h>
#include <Qt3DRender/private/abstractrenderer_p.h>
#include <Qt3DCore/private/qaspectengine_p.h>
#include <Qt3DCore/private/qaspectmanager_p.h>
#include <Qt3DCore/private/qchangearbiter_p.h>
#include <Qt3DCore/private/qservicelocator_p.h>

#include <scene3ditem_p.h>
#include <scene3dlogging_p.h>
#include <scene3dsgnode_p.h>
#include <scene3dview_p.h>

QT_BEGIN_NAMESPACE

namespace Qt3DRender {

namespace {

inline QMetaMethod setItemAreaAndDevicePixelRatioMethod()
{
    const int idx = Scene3DItem::staticMetaObject.indexOfMethod("setItemAreaAndDevicePixelRatio(QSize,qreal)");
    Q_ASSERT(idx != -1);
    return Scene3DItem::staticMetaObject.method(idx);
}

} // anonymous

class ContextSaver
{
public:
    explicit ContextSaver(QOpenGLContext *context = QOpenGLContext::currentContext())
        : m_context(context),
          m_surface(context ? context->surface() : nullptr)
    {
    }

    ~ContextSaver()
    {
        if (m_context && m_context->surface() != m_surface)
            m_context->makeCurrent(m_surface);
    }

    QOpenGLContext *context() const { return m_context; }
    QSurface *surface() const { return m_surface; }

private:
    QOpenGLContext * const m_context;
    QSurface * const m_surface;
};

/*!
    \class Qt3DRender::Scene3DRenderer
    \internal

    \brief The Scene3DRenderer class takes care of rendering a Qt3D scene
    within a Framebuffer object to be used by the QtQuick 2 renderer.

    The Scene3DRenderer class renders a Qt3D scene as provided by a Scene3DItem.
    It owns the aspectEngine even though it doesn't instantiate it.

    The render loop goes as follows:
    \list
    \li The main thread runs, drives Animations, etc. and causes changes to be
    reported to the Qt3D change arbiter. The first change reported will cause
    the scene3drenderer to be marked dirty.
    \li The QtQuick render thread starts a new frame, synchronizes the scene
    graph and emits afterSynchronizing. This will trigger some preparational
    steps for rendering and mark the QSGNode dirty if the Scene3DRenderer is
    dirty.
    \li The QtQuick render loop emits beforeRendering. If we're marked dirty or
    if the renderPolicy is set to Always, we'll ask the Qt3D renderer aspect to
    render. That call is blocking. If the aspect jobs are not done, yet, the
    renderer will exit early and we skip a frame.
    \endlist

    The shutdown procedure is a two steps process that goes as follow:

    \list
    \li The window is closed

    \li This triggers the windowsChanged signal which the Scene3DRenderer
    uses to perform the necessary cleanups in the QSGRenderThread (destroys
    DebugLogger ...) with the shutdown slot (queued connection).

    \li The destroyed signal of the window is also connected to the
    Scene3DRenderer. When triggered in the context of the main thread, the
    cleanup slot is called.
    \endlist

    There is an alternate shutdown procedure in case the QQuickItem is
    destroyed with an active window which can happen in the case where the
    Scene3D is used with a QtQuick Loader

    In that case the shutdown procedure goes the same except that the destroyed
    signal of the window is not called. Therefore the cleanup method is invoked
    to properly destroy the aspect engine.
 */
Scene3DRenderer::Scene3DRenderer()
    : QObject()
    , m_item(nullptr)
    , m_aspectEngine(nullptr)
    , m_renderAspect(nullptr)
    , m_multisampledFBO(nullptr)
    , m_finalFBO(nullptr)
    , m_texture(nullptr)
    , m_node(nullptr)
    , m_window(nullptr)
    , m_multisample(false) // this value is not used, will be synced from the Scene3DItem instead
    , m_lastMultisample(false)
    , m_needsShutdown(true)
    , m_forceRecreate(false)
    , m_shouldRender(false)
    , m_dirtyViews(false)
    , m_skipFrame(false)
    , m_allowRendering(0)
    , m_compositingMode(Scene3DItem::FBO)
{

}

void Scene3DRenderer::init(Scene3DItem *item, Qt3DCore::QAspectEngine *aspectEngine,
                           QRenderAspect *renderAspect)
{
    m_item = item;
    m_aspectEngine = aspectEngine;
    m_renderAspect = renderAspect;
    m_needsShutdown = true;

    Q_CHECK_PTR(m_item);
    Q_CHECK_PTR(m_item->window());

    m_window = m_item->window();
    QObject::connect(m_item->window(), &QQuickWindow::beforeSynchronizing, this, &Scene3DRenderer::beforeSynchronize, Qt::DirectConnection);
    QObject::connect(m_item->window(), &QQuickWindow::beforeRendering, this, &Scene3DRenderer::render, Qt::DirectConnection);
    QObject::connect(m_item->window(), &QQuickWindow::sceneGraphInvalidated, this, &Scene3DRenderer::onSceneGraphInvalidated, Qt::DirectConnection);
    // So that we can schedule the cleanup
    QObject::connect(m_item, &QQuickItem::windowChanged, this, &Scene3DRenderer::onWindowChanged, Qt::QueuedConnection);
    // Main thread -> updates the rendering window
    QObject::connect(m_item, &QQuickItem::windowChanged, this, [this] (QQuickWindow *w) {
        QMutexLocker l(&m_windowMutex);
        m_window = w;
    });

    Q_ASSERT(QOpenGLContext::currentContext());
    ContextSaver saver;
    static_cast<QRenderAspectPrivate*>(QRenderAspectPrivate::get(m_renderAspect))->renderInitialize(saver.context());
    scheduleRootEntityChange();
}

Scene3DRenderer::~Scene3DRenderer()
{
    qCDebug(Scene3D) << Q_FUNC_INFO << QThread::currentThread();
}


QOpenGLFramebufferObject *Scene3DRenderer::createMultisampledFramebufferObject(const QSize &size)
{
    QOpenGLFramebufferObjectFormat format;
    format.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
    int samples = QSurfaceFormat::defaultFormat().samples();
    if (samples == -1)
        samples = 4;
    format.setSamples(samples);
    return new QOpenGLFramebufferObject(size, format);
}

QOpenGLFramebufferObject *Scene3DRenderer::createFramebufferObject(const QSize &size)
{
    QOpenGLFramebufferObjectFormat format;
    format.setAttachment(QOpenGLFramebufferObject::Depth);
    return new QOpenGLFramebufferObject(size, format);
}

void Scene3DRenderer::scheduleRootEntityChange()
{
    QMetaObject::invokeMethod(m_item, "applyRootEntityChange", Qt::QueuedConnection);
}

// Executed in the QtQuick render thread (which may even be the gui/main with QQuickWidget / RenderControl).
void Scene3DRenderer::shutdown()
{
    qCDebug(Scene3D) << Q_FUNC_INFO << QThread::currentThread();

    // In case the same item is rendered on another window reset it
    m_resetRequested = true;

    // Set to null so that subsequent calls to render
    // would return early
    m_item = nullptr;

    // Exit the simulation loop so no more jobs are asked for. Once this
    // returns it is safe to shutdown the renderer.
    if (m_aspectEngine) {
        auto engineD = Qt3DCore::QAspectEnginePrivate::get(m_aspectEngine);
        engineD->exitSimulationLoop();
    }

    // Shutdown the Renderer Aspect while the OpenGL context
    // is still valid
    if (m_renderAspect) {
        static_cast<QRenderAspectPrivate*>(QRenderAspectPrivate::get(m_renderAspect))->renderShutdown();
        m_renderAspect = nullptr;
    }
    m_aspectEngine = nullptr;
    m_finalFBO.reset();
    m_multisampledFBO.reset();
}

// QtQuick render thread (which may also be the gui/main thread with QQuickWidget / RenderControl)
void Scene3DRenderer::onSceneGraphInvalidated()
{
    qCDebug(Scene3D) << Q_FUNC_INFO << QThread::currentThread();
    if (m_needsShutdown) {
        m_needsShutdown = false;
        shutdown();
    }
}

void Scene3DRenderer::onWindowChanged(QQuickWindow *w)
{
    qCDebug(Scene3D) << Q_FUNC_INFO << QThread::currentThread() << w;
    if (!w) {
        if (m_needsShutdown) {
            m_needsShutdown = false;
            shutdown();
        }
    }
}

// Render Thread, GUI locked
void Scene3DRenderer::beforeSynchronize()
{
    if (m_item && m_window) {

        // Only render if we are sure aspectManager->processFrame was called prior
        // We could otherwise enter a deadlock state
        if (!m_allowRendering.tryAcquire(std::max(m_allowRendering.available(), 1)))
            return;

        // In the case of OnDemand rendering, we still need to get to this
        // point to ensure we have processed jobs for all aspects.
        // We also still need to call render() to allow proceeding with the
        // next frame. However it won't be performing any 3d rendering at all
        // so we do it here and return early. This prevents a costly QtQuick
        // SceneGraph update for nothing
        if (m_skipFrame) {
            m_skipFrame = false;
            ContextSaver saver;
            static_cast<QRenderAspectPrivate*>(QRenderAspectPrivate::get(m_renderAspect))->renderSynchronous(false);
            return;
        }

        m_shouldRender = true;

        // Check size / multisampling
        m_multisample = m_item->multisample();
        const QSize boundingRectSize = m_item->boundingRect().size().toSize();
        const QSize currentSize = boundingRectSize * m_window->effectiveDevicePixelRatio();
        const bool sizeHasChanged = currentSize != m_lastSize;
        const bool multisampleHasChanged = m_multisample != m_lastMultisample;
        const bool forceRecreate = sizeHasChanged || multisampleHasChanged;
        // Store the current size as a comparison
        // point for the next frame
        m_lastSize = currentSize;
        m_lastMultisample = m_multisample;

        if (sizeHasChanged) {
            static const QMetaMethod setItemAreaAndDevicePixelRatio = setItemAreaAndDevicePixelRatioMethod();
            setItemAreaAndDevicePixelRatio.invoke(m_item, Qt::QueuedConnection, Q_ARG(QSize, boundingRectSize),
                                                  Q_ARG(qreal, m_window->effectiveDevicePixelRatio()));
        }

        // Rebuild FBO if size/multisampling has changed
        const bool usesFBO = m_compositingMode == Scene3DItem::FBO;
        if (usesFBO) {
            // Rebuild FBO and textures if never created or a resize has occurred
            if ((m_multisampledFBO.isNull() || forceRecreate) && m_multisample) {
                m_multisampledFBO.reset(createMultisampledFramebufferObject(m_lastSize));
                if (m_multisampledFBO->format().samples() == 0 || !QOpenGLFramebufferObject::hasOpenGLFramebufferBlit()) {
                    m_multisample = false;
                    m_multisampledFBO.reset(nullptr);
                }
            }

            const bool generateNewTexture = m_finalFBO.isNull() || forceRecreate;
            if (generateNewTexture) {
                m_finalFBO.reset(createFramebufferObject(m_lastSize));
                m_texture.reset(m_window->createTextureFromId(m_finalFBO->texture(), m_finalFBO->size(), QQuickWindow::TextureHasAlphaChannel));
            }

            // We can render either the Scene3D or the Scene3DView but not both
            // at the same time
            Q_ASSERT((m_node == nullptr || m_views.empty()) ||
                     (m_node != nullptr && m_views.empty()) ||
                     (m_node == nullptr && !m_views.empty()));

            // Set texture on node
            if (m_node && (!m_node->texture() || generateNewTexture))
                m_node->setTexture(m_texture.data());

            // Set textures on Scene3DView
            if (m_dirtyViews || generateNewTexture) {
                for (Scene3DView *view : qAsConst(m_views))
                    if (!view->texture() || generateNewTexture)
                        view->setTexture(m_texture.data());
                m_dirtyViews = false;
            }
        }

        if (m_aspectEngine->rootEntity() != m_item->entity()) {
            scheduleRootEntityChange();
        }

        // Mark SGNodes as dirty so that QQuick will trigger some rendering
        if (m_node)
            m_node->markDirty(QSGNode::DirtyMaterial);

        for (Scene3DView *view : qAsConst(m_views))
            view->markSGNodeDirty();

        m_item->update();
    }
}

void Scene3DRenderer::allowRender()
{
    m_allowRendering.release(1);
}

void Scene3DRenderer::setCompositingMode(Scene3DItem::CompositingMode mode)
{
    m_compositingMode = mode;
}

void Scene3DRenderer::setSkipFrame(bool skip)
{
    m_skipFrame = skip;
}

// Main Thread, Render Thread locked
void Scene3DRenderer::setScene3DViews(const QVector<Scene3DView *> views)
{
    m_views = views;
    m_dirtyViews = true;
}

void Scene3DRenderer::setSGNode(Scene3DSGNode *node)
{
    m_node = node;
}

// Render Thread, Main Thread is unlocked at this point
void Scene3DRenderer::render()
{
    QMutexLocker l(&m_windowMutex);
    // Lock to ensure the window doesn't change while we are rendering
    if (!m_window || !m_shouldRender)
        return;
    m_shouldRender = false;

    ContextSaver saver;

    // The OpenGL state may be dirty from the previous QtQuick nodes, so reset
    // it here to give Qt3D the clean state it expects
    m_window->resetOpenGLState();

    // Create and bind FBO if using the FBO compositing mode
    const bool usesFBO = m_compositingMode == Scene3DItem::FBO;
    if (usesFBO) {
        // Bind FBO
        if (m_multisample) //Only try to use MSAA when available
            m_multisampledFBO->bind();
        else
            m_finalFBO->bind();
    }

    // Render Qt3D Scene
    static_cast<QRenderAspectPrivate*>(QRenderAspectPrivate::get(m_renderAspect))->renderSynchronous(usesFBO);

    // We may have called doneCurrent() so restore the context if the rendering surface was changed
    // Note: keep in mind that the ContextSave also restores the surface when destroyed
    if (saver.context()->surface() != saver.surface())
        saver.context()->makeCurrent(saver.surface());

    if (usesFBO) {
        if (m_multisample) {
            // Blit multisampled FBO with non multisampled FBO with texture attachment
            const QRect dstRect(QPoint(0, 0), m_finalFBO->size());
            const QRect srcRect(QPoint(0, 0), m_multisampledFBO->size());
            QOpenGLFramebufferObject::blitFramebuffer(m_finalFBO.data(), dstRect,
                                                      m_multisampledFBO.data(), srcRect,
                                                      GL_COLOR_BUFFER_BIT,
                                                      GL_NEAREST,
                                                      0, 0,
                                                      QOpenGLFramebufferObject::DontRestoreFramebufferBinding);
        }

        // Restore QtQuick FBO
        QOpenGLFramebufferObject::bindDefault();

        // Only show the node once Qt3D has rendered to it
        // Avoids showing garbage on the first frame
        if (m_node)
            m_node->show();
    }

    // Reset the state used by the Qt Quick scenegraph to avoid any
    // interference when rendering the rest of the UI.
    m_window->resetOpenGLState();
}

} // namespace Qt3DRender

QT_END_NAMESPACE
