BGE performance: second round of scenegraph improvement.

Use dynamic linked list to handle scenegraph rather than dumb scan
of the whole tree. The performance improvement depends on the fraction
of moving objects. If most objects are static, the speed up is 
considerable. The following table compares the time spent on 
scenegraph before and after this commit on a scene with 10000 objects
in various configuratons:

Scenegraph time (ms)              Before         After
(includes culling)

All objects static,               8.8            1.7  
all visible but small fraction          
in the view frustrum

All objects static,               7,5            0.01
all invisible.

All objects moving,               14.1           8.4
all visible but small fraction
in the view frustrum

This tables shows that static and invisible objects take no CPU at all
for scenegraph and culling. In the general case, this commit will 
speed up the scenegraph between 2x and 5x. Compared to 2.48a, it should
be between 4x and 10x faster. Further speed up is possible by making
the scenegraph cache-friendly.

Next round of performance improvement will be on the rasterizer: use
the same dynamic linked list technique for the mesh slots.

1 files changed, 34 insertions, 6 deletions

diff --git a/source/gameengine/Ketsji/KX_Scene.cpp b/source/gameengine/Ketsji/KX_Scene.cpp
index 171ed5d130f..d31d451f02e 100644
--- a/source/gameengine/Ketsji/KX_Scene.cpp
+++ b/source/gameengine/Ketsji/KX_Scene.cpp
@@ -111,7 +111,22 @@ void* KX_SceneDestructionFunc(SG_IObject* node,void* gameobj,void* scene)
 	return NULL;
 };
 
-SG_Callbacks KX_Scene::m_callbacks = SG_Callbacks(KX_SceneReplicationFunc,KX_SceneDestructionFunc,KX_GameObject::UpdateTransformFunc);
+bool KX_Scene::KX_ScenegraphUpdateFunc(SG_IObject* node,void* gameobj,void* scene)
+{
+	return ((SG_Node*)node)->Schedule(((KX_Scene*)scene)->m_sghead);
+}
+
+bool KX_Scene::KX_ScenegraphRescheduleFunc(SG_IObject* node,void* gameobj,void* scene)
+{
+	return ((SG_Node*)node)->Reschedule(((KX_Scene*)scene)->m_sghead);
+}
+
+SG_Callbacks KX_Scene::m_callbacks = SG_Callbacks(
+	KX_SceneReplicationFunc,
+	KX_SceneDestructionFunc,
+	KX_GameObject::UpdateTransformFunc,
+	KX_Scene::KX_ScenegraphUpdateFunc,
+	KX_Scene::KX_ScenegraphRescheduleFunc);
 
 // temporarily var until there is a button in the userinterface
 // (defined in KX_PythonInit.cpp)
@@ -1473,15 +1488,28 @@ void KX_Scene::LogicEndFrame()
   */
 void KX_Scene::UpdateParents(double curtime)
 {
-//	int numrootobjects = GetRootParentList()->GetCount();
+	// we use the SG dynamic list
+	SG_Node* node;
 
-	for (int i=0; i<GetRootParentList()->GetCount(); i++)
+	while ((node = SG_Node::GetNextScheduled(m_sghead)) != NULL)
 	{
-		KX_GameObject* parentobj = (KX_GameObject*)GetRootParentList()->GetValue(i);
-		parentobj->NodeUpdateGS(curtime);
+		node->UpdateWorldData(curtime);
 	}
-}
 
+	//for (int i=0; i<GetRootParentList()->GetCount(); i++)
+	//{
+	//	KX_GameObject* parentobj = (KX_GameObject*)GetRootParentList()->GetValue(i);
+	//	parentobj->NodeUpdateGS(curtime);
+	//}
+
+	// the list must be empty here
+	assert(m_sghead.Empty());
+	// some nodes may be ready for reschedule, move them to schedule list for next time
+	while ((node = SG_Node::GetNextRescheduled(m_sghead)) != NULL)
+	{
+		node->Schedule(m_sghead);
+	}
+}
 
 
 RAS_MaterialBucket* KX_Scene::FindBucket(class RAS_IPolyMaterial* polymat, bool &bucketCreated)