BGE: New hysteresis offset to improve LOD level transitions

This change introduces a new hysteresis parameter that it will be added
or subtracted to/from the LOD distance to avoid popping when a LOD
object moves close to the LOD transition continuously.

Then, we have the following:

- a new LOD Hysteresis setting per scene (default 10%) which is located
in Scene context --> Level of Detail panel. This scene parameter also
will active/deactive the scene hysteresis.
- and a new LOD Hysteresis setting per object (default 10%) which is
located in Object context --> Levels of Detail panel. The LOD hysteresis
setting per object (if active) will overwrite the hysteresis setting per
scene value.

For the new blends: the hysteresis setting per scene would be active by
default and the per object would be inactive by default.
For the old blends: both hysteresis settings (per scene and per object)
would be inactive by default. A quick way to take advantage of this
feature for old blends would be to activate the hysteresis parameter in
the scene context -> Level of Detail panel

Reviewers: campbellbarton, kupoman, moguri

Reviewed By: kupoman, moguri

Subscribers: nonamejuju, lordodin

Differential Revision: https://developer.blender.org/D957

5 files changed, 76 insertions, 2 deletions

diff --git a/source/gameengine/Converter/BL_BlenderDataConversion.cpp b/source/gameengine/Converter/BL_BlenderDataConversion.cpp
index cd2e2151034..7b5cc457ee6 100644
--- a/source/gameengine/Converter/BL_BlenderDataConversion.cpp
+++ b/source/gameengine/Converter/BL_BlenderDataConversion.cpp
@@ -1554,6 +1554,10 @@ static KX_GameObject *gameobject_from_blenderobject(
 				}
 				gameobj->AddLodMesh(BL_ConvertMesh(lodmesh, lodmatob, kxscene, converter, libloading));
 			}
+			if (blenderscene->gm.lodflag & SCE_LOD_USE_HYST) {
+				kxscene->SetLodHysteresis(true);
+				gameobj->SetLodHysteresisValue(blenderscene->gm.scehysteresis);
+			}
 		}
 	
 		// for all objects: check whether they want to
diff --git a/source/gameengine/Ketsji/KX_GameObject.cpp b/source/gameengine/Ketsji/KX_GameObject.cpp
index c8fc64f4679..16dfe5bd9de 100644
--- a/source/gameengine/Ketsji/KX_GameObject.cpp
+++ b/source/gameengine/Ketsji/KX_GameObject.cpp
@@ -92,6 +92,8 @@ KX_GameObject::KX_GameObject(
       m_bDyna(false),
       m_layer(0),
       m_currentLodLevel(0),
+      m_previousLodLevel(0),
+      m_lodHysteresis(0),
       m_pBlenderObject(NULL),
       m_pBlenderGroupObject(NULL),
       m_bSuspendDynamics(false),
@@ -784,6 +786,11 @@ void KX_GameObject::AddLodMesh(RAS_MeshObject* mesh)
 	m_lodmeshes.push_back(mesh);
 }
 
+void KX_GameObject::SetLodHysteresisValue(int hysteresis)
+{
+	m_lodHysteresis = hysteresis;
+}
+
 void KX_GameObject::UpdateLod(MT_Vector3 &cam_pos)
 {
 	// Handle dupligroups
@@ -804,14 +811,47 @@ void KX_GameObject::UpdateLod(MT_Vector3 &cam_pos)
 	int level = 0;
 	Object *bob = this->GetBlenderObject();
 	LodLevel *lod = (LodLevel*) bob->lodlevels.first;
+	KX_Scene *sce = this->GetScene();
+
 	for (; lod; lod = lod->next, level++) {
 		if (!lod->source || lod->source->type != OB_MESH) level--;
-		if (!lod->next || lod->next->distance * lod->next->distance > distance2) break;
+		if (!lod->next) break;
+		if (level == (this->m_previousLodLevel) || (level == (this->m_previousLodLevel + 1))) {
+			short hysteresis = 0;
+			if (sce->IsActivedLodHysteresis()) {
+				// if exists, LoD level hysteresis will override scene hysteresis
+				if (lod->next->flags & OB_LOD_USE_HYST) {
+					hysteresis = lod->next->obhysteresis;
+				}
+				else if (this->m_lodHysteresis != 0) {
+					hysteresis = m_lodHysteresis;
+				}
+			}
+			float hystvariance = MT_abs(lod->next->distance - lod->distance) * hysteresis / 100;
+			if ((lod->next->distance + hystvariance) * (lod->next->distance + hystvariance) > distance2)
+				break;
+		}
+		else if (level == (this->m_previousLodLevel - 1)) {
+			short hysteresis = 0;
+			if (sce->IsActivedLodHysteresis()) {
+				// if exists, LoD level hysteresis will override scene hysteresis
+				if (lod->next->flags & OB_LOD_USE_HYST) {
+					hysteresis = lod->next->obhysteresis;
+				}
+				else if (this->m_lodHysteresis != 0) {
+					hysteresis = m_lodHysteresis;
+				}
+			}
+			float hystvariance = MT_abs(lod->next->distance - lod->distance) * hysteresis / 100;
+			if ((lod->next->distance - hystvariance) * (lod->next->distance - hystvariance) > distance2)
+				break;
+		}
 	}
 
 	RAS_MeshObject *mesh = this->m_lodmeshes[level];
 	this->m_currentLodLevel = level;
 	if (mesh != this->m_meshes[0]) {
+		this->m_previousLodLevel = level;
 		this->GetScene()->ReplaceMesh(this, mesh, true, false);
 	}
 }
diff --git a/source/gameengine/Ketsji/KX_GameObject.h b/source/gameengine/Ketsji/KX_GameObject.h
index 132e72c45e2..d9810b89c90 100644
--- a/source/gameengine/Ketsji/KX_GameObject.h
+++ b/source/gameengine/Ketsji/KX_GameObject.h
@@ -90,6 +90,8 @@ protected:
 	std::vector<RAS_MeshObject*>		m_meshes;
 	std::vector<RAS_MeshObject*>		m_lodmeshes;
 	int                                 m_currentLodLevel;
+	short								m_previousLodLevel;
+	int									m_lodHysteresis;
 	SG_QList							m_meshSlots;	// head of mesh slots of this 
 	struct Object*						m_pBlenderObject;
 	struct Object*						m_pBlenderGroupObject;
@@ -805,6 +807,14 @@ public:
 	);
 
 	/**
+	 * Set lod hysteresis value
+	 */
+		void
+	SetLodHysteresisValue(
+		int hysteresis
+	);
+
+	/**
 	 * Updates the current lod level based on distance from camera.
 	 */
 		void
diff --git a/source/gameengine/Ketsji/KX_Scene.cpp b/source/gameengine/Ketsji/KX_Scene.cpp
index 47510baa436..d9d07e78c17 100644
--- a/source/gameengine/Ketsji/KX_Scene.cpp
+++ b/source/gameengine/Ketsji/KX_Scene.cpp
@@ -156,7 +156,8 @@ KX_Scene::KX_Scene(class SCA_IInputDevice* keyboarddevice,
 	m_networkDeviceInterface(ndi),
 	m_active_camera(NULL),
 	m_ueberExecutionPriority(0),
-	m_blenderScene(scene)
+	m_blenderScene(scene),
+	m_isActivedHysteresis(false)
 {
 	m_suspendedtime = 0.0;
 	m_suspendeddelta = 0.0;
@@ -1763,6 +1764,16 @@ void KX_Scene::UpdateObjectLods(void)
 	}
 }
 
+void KX_Scene::SetLodHysteresis(bool active)
+{
+	m_isActivedHysteresis = active;
+}
+
+bool KX_Scene::IsActivedLodHysteresis(void)
+{
+	return m_isActivedHysteresis;
+}
+
 void KX_Scene::UpdateObjectActivity(void) 
 {
 	if (m_activity_culling) {
diff --git a/source/gameengine/Ketsji/KX_Scene.h b/source/gameengine/Ketsji/KX_Scene.h
index 2e1ee9f101d..19873daabb3 100644
--- a/source/gameengine/Ketsji/KX_Scene.h
+++ b/source/gameengine/Ketsji/KX_Scene.h
@@ -295,6 +295,11 @@ protected:
 
 	KX_ObstacleSimulation* m_obstacleSimulation;
 
+	/**
+	 * Does this scene active the LoD Hysteresis?
+	 */
+	bool m_isActivedHysteresis;
+
 public:
 	KX_Scene(class SCA_IInputDevice* keyboarddevice,
 		class SCA_IInputDevice* mousedevice,
@@ -546,6 +551,10 @@ public:
 
 	// Update the mesh for objects based on level of detail settings
 	void UpdateObjectLods(void);
+
+	// Enable/disable LoD Hysteresis
+	void SetLodHysteresis(bool active);
+	bool IsActivedLodHysteresis();
 	
 	// Update the activity box settings for objects in this scene, if needed.
 	void UpdateObjectActivity(void);