Add video filtering support to VideoOutput

Add the QAbstractVideoFilter base class and integrate it with VideoOutput.

This can be used to perform arbitrary filtering or image processing
on the frames of a video stream of a VideoOutput element right before
the OpenGL texture is provided to the scenegraph by the video node.

This opens up the possibility to integrate computer vision
frameworks or accelerated image processing with Qt Quick applications
that display video streams using Qt Multimedia.

Conceptually it is somewhat similar to QVideoProbe, this
approach however allows modifying the frame, in real time
with tight integration to the scenegraph node, and targets
Qt Quick meaning setting up the filter and processing the results
of the computations happen completely in QML.

[ChangeLog] Added QAbstractVideoFilter that serves as a base class for QML
video filtering elements that integrate compute, vision, and image processing
frameworks with VideoOutput.

Change-Id: Ice1483f8c2daec5a43536978627a7bbb64549480
Reviewed-by: Yoann Lopes <yoann.lopes@theqtcompany.com>

src/qtmultimediaquicktools/qdeclarativevideooutput_render.cpp

@@ -34,6 +34,7 @@
 
 #include "qdeclarativevideooutput_render_p.h"
 #include "qdeclarativevideooutput_p.h"
+#include <QtMultimedia/qabstractvideofilter.h>
 #include <QtMultimedia/qvideorenderercontrol.h>
 #include <QtMultimedia/qmediaservice.h>
 #include <QtCore/qloggingcategory.h>
@@ -41,6 +42,8 @@
 #include <private/qsgvideonode_p.h>
 
 #include <QtGui/QOpenGLContext>
+#include <QtQuick/QQuickWindow>
+#include <QtCore/QRunnable>
 
 QT_BEGIN_NAMESPACE
 
@@ -103,11 +106,79 @@ bool QDeclarativeVideoRendererBackend::init(QMediaService *service)
     return false;
 }
 
+void QDeclarativeVideoRendererBackend::appendFilter(QAbstractVideoFilter *filter)
+{
+    QMutexLocker lock(&m_frameMutex);
+    m_filters.append(Filter(filter));
+}
+
+void QDeclarativeVideoRendererBackend::clearFilters()
+{
+    QMutexLocker lock(&m_frameMutex);
+    scheduleDeleteFilterResources();
+    m_filters.clear();
+}
+
+class FilterRunnableDeleter : public QRunnable
+{
+public:
+    FilterRunnableDeleter(const QList<QVideoFilterRunnable *> &runnables) : m_runnables(runnables) { }
+    void run() Q_DECL_OVERRIDE {
+        foreach (QVideoFilterRunnable *runnable, m_runnables)
+            delete runnable;
+    }
+private:
+    QList<QVideoFilterRunnable *> m_runnables;
+};
+
+void QDeclarativeVideoRendererBackend::scheduleDeleteFilterResources()
+{
+    if (!q->window())
+        return;
+
+    QList<QVideoFilterRunnable *> runnables;
+    for (int i = 0; i < m_filters.count(); ++i) {
+        if (m_filters[i].runnable) {
+            runnables.append(m_filters[i].runnable);
+            m_filters[i].runnable = 0;
+        }
+    }
+
+    if (!runnables.isEmpty()) {
+        // Request the scenegraph to run our cleanup job on the render thread.
+        // The execution of our QRunnable may happen after the QML tree including the QAbstractVideoFilter instance is
+        // destroyed on the main thread so no references to it must be used during cleanup.
+        q->window()->scheduleRenderJob(new FilterRunnableDeleter(runnables), QQuickWindow::BeforeSynchronizingStage);
+    }
+}
+
+void QDeclarativeVideoRendererBackend::releaseResources()
+{
+    // Called on the gui thread when the window is closed or changed.
+    QMutexLocker lock(&m_frameMutex);
+    scheduleDeleteFilterResources();
+}
+
+void QDeclarativeVideoRendererBackend::invalidateSceneGraph()
+{
+    // Called on the render thread, e.g. when the context is lost.
+    QMutexLocker lock(&m_frameMutex);
+    for (int i = 0; i < m_filters.count(); ++i) {
+        if (m_filters[i].runnable) {
+            delete m_filters[i].runnable;
+            m_filters[i].runnable = 0;
+        }
+    }
+}
+
 void QDeclarativeVideoRendererBackend::itemChange(QQuickItem::ItemChange change,
                                       const QQuickItem::ItemChangeData &changeData)
 {
-    Q_UNUSED(change);
-    Q_UNUSED(changeData);
+    if (change == QQuickItem::ItemSceneChange) {
+        if (changeData.window)
+            QObject::connect(changeData.window, SIGNAL(sceneGraphInvalidated()),
+                             q, SLOT(_q_invalidateSceneGraph()), Qt::DirectConnection);
+    }
 }
 
 void QDeclarativeVideoRendererBackend::releaseSource()
@@ -216,8 +287,36 @@ QSGNode *QDeclarativeVideoRendererBackend::updatePaintNode(QSGNode *oldNode,
     }
 #endif
 
+    bool isFrameModified = false;
     if (m_frameChanged) {
-        if (videoNode && videoNode->pixelFormat() != m_frame.pixelFormat()) {
+        // Run the VideoFilter if there is one. This must be done before potentially changing the videonode below.
+        if (m_frame.isValid() && !m_filters.isEmpty()) {
+            const QVideoSurfaceFormat surfaceFormat = videoSurface()->surfaceFormat();
+            for (int i = 0; i < m_filters.count(); ++i) {
+                QAbstractVideoFilter *filter = m_filters[i].filter;
+                QVideoFilterRunnable *&runnable = m_filters[i].runnable;
+                if (filter && filter->isActive()) {
+                    // Create the filter runnable if not yet done. Ownership is taken and is tied to this thread, on which rendering happens.
+                    if (!runnable)
+                        runnable = filter->createFilterRunnable();
+                    if (!runnable)
+                        continue;
+
+                    QVideoFilterRunnable::RunFlags flags = 0;
+                    if (i == m_filters.count() - 1)
+                        flags |= QVideoFilterRunnable::LastInChain;
+
+                    QVideoFrame newFrame = runnable->run(&m_frame, surfaceFormat, flags);
+
+                    if (newFrame.isValid() && newFrame != m_frame) {
+                        isFrameModified = true;
+                        m_frame = newFrame;
+                    }
+                }
+            }
+        }
+
+        if (videoNode && (videoNode->pixelFormat() != m_frame.pixelFormat() || videoNode->handleType() != m_frame.handleType())) {
             qCDebug(qLcVideo) << "updatePaintNode: deleting old video node because frame format changed";
             delete videoNode;
             videoNode = 0;
@@ -231,7 +330,9 @@ QSGNode *QDeclarativeVideoRendererBackend::updatePaintNode(QSGNode *oldNode,
 
         if (!videoNode) {
             foreach (QSGVideoNodeFactoryInterface* factory, m_videoNodeFactories) {
-                videoNode = factory->createNode(m_surface->surfaceFormat());
+                // Get a node that supports our frame. The surface is irrelevant, our
+                // QSGVideoItemSurface supports (logically) anything.
+                videoNode = factory->createNode(QVideoSurfaceFormat(m_frame.size(), m_frame.pixelFormat(), m_frame.handleType()));
                 if (videoNode) {
                     qCDebug(qLcVideo) << "updatePaintNode: Video node created. Handle type:" << m_frame.handleType()
                                      << " Supported formats for the handle by this node:"
@@ -252,7 +353,10 @@ QSGNode *QDeclarativeVideoRendererBackend::updatePaintNode(QSGNode *oldNode,
     videoNode->setTexturedRectGeometry(m_renderedRect, m_sourceTextureRect,
                                        qNormalizedOrientation(q->orientation()));
     if (m_frameChanged) {
-        videoNode->setCurrentFrame(m_frame);
+        QSGVideoNode::FrameFlags flags = 0;
+        if (isFrameModified)
+            flags |= QSGVideoNode::FrameFiltered;
+        videoNode->setCurrentFrame(m_frame, flags);
         //don't keep the frame for more than really necessary
         m_frameChanged = false;
         m_frame = QVideoFrame();