Add private API to access child nodes of QEntity and QFrameGraphNode

This opens up for reduced bookeeping on the backend,
and is used by the experimental Dragon render aspect,
which is currently being implemented in qt3d-runtime.

Change-Id: I4cc2e98e4e0e7e8d456ed11c4fbc48db5c93f2a2
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>
(cherry picked from commit 77e418fde850c86e39d9dd8528876599fbe9dc34)
Reviewed-by: Mike Krus <mike.krus@kdab.com>
Reviewed-by: Christian Stromme <christian.stromme@qt.io>

1 files changed, 35 insertions, 1 deletions

diff --git a/src/render/framegraph/qframegraphnode.cpp b/src/render/framegraph/qframegraphnode.cpp
index 0a60edef7..3cf19d0d8 100644
--- a/src/render/framegraph/qframegraphnode.cpp
+++ b/src/render/framegraph/qframegraphnode.cpp
@@ -41,6 +41,12 @@
 #include "qframegraphnode_p.h"
 #include <Qt3DRender/qframegraphnodecreatedchange.h>
 
+#include <Qt3DCore/QNode>
+
+#include <QQueue>
+
+using namespace Qt3DCore;
+
 QT_BEGIN_NAMESPACE
 
 namespace Qt3DRender {
@@ -190,7 +196,10 @@ QFrameGraphNode::~QFrameGraphNode()
 }
 
 /*!
-    Returns a pointer to the parent.
+    Returns a pointer to the parent frame graph node.
+
+    If the parent of this node is not a frame graph node,
+    this method will recursively look for a parent node that is a frame graph node.
  */
 QFrameGraphNode *QFrameGraphNode::parentFrameGraphNode() const
 {
@@ -205,6 +214,31 @@ QFrameGraphNode *QFrameGraphNode::parentFrameGraphNode() const
     return parentFGNode;
 }
 
+/*!
+ * Returns a list of the children that are frame graph nodes.
+ * If this function encounters a child node that is not a frame graph node,
+ * it will go through the children of the child node and look for frame graph nodes.
+ * If any of these are not frame graph nodes, they will be further searched as
+ * if they were direct children of this node.
+ */
+QVector<QFrameGraphNode *> QFrameGraphNodePrivate::childFrameGraphNodes() const
+{
+    Q_Q(const QFrameGraphNode);
+    QVector<QFrameGraphNode *> result;
+    QQueue<QNode *> queue;
+    queue.append(q->childNodes().toList());
+    result.reserve(queue.size());
+    while (!queue.isEmpty()) {
+        auto *child = queue.dequeue();
+        auto *childFGNode = qobject_cast<QFrameGraphNode *>(child);
+        if (childFGNode != nullptr)
+            result.push_back(childFGNode);
+        else
+            queue.append(child->childNodes().toList());
+    }
+    return result;
+}
+
 /*! \internal */
 QFrameGraphNode::QFrameGraphNode(QFrameGraphNodePrivate &dd, QNode *parent)
     : QNode(dd, parent)