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

13 files changed, 141 insertions, 4 deletions

diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index 08a74d0c6cd..174fb38aada 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -1098,10 +1098,12 @@ void BKE_object_lod_add(Object *ob)
 		BLI_addtail(&ob->lodlevels, base);
 		base->flags = OB_LOD_USE_MESH | OB_LOD_USE_MAT;
 		base->source = ob;
+		base->obhysteresis = 10;
 		last = ob->currentlod = base;
 	}
 	
 	lod->distance = last->distance + 25.0f;
+	lod->obhysteresis = 10;
 	lod->flags = OB_LOD_USE_MESH | OB_LOD_USE_MAT;
 
 	BLI_addtail(&ob->lodlevels, lod);
diff --git a/source/blender/blenkernel/intern/scene.c b/source/blender/blenkernel/intern/scene.c
index c28d741d7ec..d2c3f473e11 100644
--- a/source/blender/blenkernel/intern/scene.c
+++ b/source/blender/blenkernel/intern/scene.c
@@ -677,6 +677,9 @@ Scene *BKE_scene_add(Main *bmain, const char *name)
 	sce->gm.recastData.detailsampledist = 6.0f;
 	sce->gm.recastData.detailsamplemaxerror = 1.0f;
 
+	sce->gm.lodflag = SCE_LOD_USE_HYST;
+	sce->gm.scehysteresis = 10;
+
 	sce->gm.exitkey = 218; // Blender key code for ESC
 
 	sound_create_scene(sce);
diff --git a/source/blender/blenloader/intern/versioning_270.c b/source/blender/blenloader/intern/versioning_270.c
index adf5f93ae16..0853c93750c 100644
--- a/source/blender/blenloader/intern/versioning_270.c
+++ b/source/blender/blenloader/intern/versioning_270.c
@@ -654,5 +654,23 @@ void blo_do_versions_270(FileData *fd, Library *UNUSED(lib), Main *main)
 				}
 			}
 		}
+
+		/* hysteresis setted to 10% but not actived */
+		if (!DNA_struct_elem_find(fd->filesdna, "LodLevel", "int", "obhysteresis")) {
+			Object* ob;
+			for (ob = main->object.first; ob; ob = ob->id.next) {
+				LodLevel *level;
+				for (level = ob->lodlevels.first; level; level = level->next) {
+					level->obhysteresis = 10;
+				}
+			}
+		}
+
+		if (!DNA_struct_elem_find(fd->filesdna, "GameData", "int", "scehysteresis")) {
+			Scene *scene;
+			for (scene = main->scene.first; scene; scene = scene->id.next) {
+				scene->gm.scehysteresis = 10;
+			}
+		}
 	}
 }
diff --git a/source/blender/blenloader/intern/versioning_defaults.c b/source/blender/blenloader/intern/versioning_defaults.c
index 4c7b011097b..d320b305c06 100644
--- a/source/blender/blenloader/intern/versioning_defaults.c
+++ b/source/blender/blenloader/intern/versioning_defaults.c
@@ -92,6 +92,9 @@ void BLO_update_defaults_startup_blend(Main *bmain)
 				sculpt->detail_size = 12;
 			}
 		}
+
+		scene->gm.lodflag |= SCE_LOD_USE_HYST;
+		scene->gm.scehysteresis = 10;
 	}
 
 	for (linestyle = bmain->linestyle.first; linestyle; linestyle = linestyle->id.next) {
diff --git a/source/blender/makesdna/DNA_object_types.h b/source/blender/makesdna/DNA_object_types.h
index 2699bb5f22f..4cb979c57b7 100644
--- a/source/blender/makesdna/DNA_object_types.h
+++ b/source/blender/makesdna/DNA_object_types.h
@@ -109,7 +109,8 @@ typedef struct LodLevel {
 	struct LodLevel *next, *prev;
 	struct Object *source;
 	int flags;
-	float distance;
+	float distance, pad;
+	int obhysteresis;
 } LodLevel;
 
 typedef struct Object {
@@ -484,6 +485,7 @@ enum {
 enum {
 	OB_LOD_USE_MESH		= 1 << 0,
 	OB_LOD_USE_MAT		= 1 << 1,
+	OB_LOD_USE_HYST		= 1 << 2,
 };
 
 
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 0eae50a2562..ac0803d494c 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -718,7 +718,12 @@ typedef struct GameData {
 	short obstacleSimulation;
 	short raster_storage;
 	float levelHeight;
-	float deactivationtime, lineardeactthreshold, angulardeactthreshold, pad2;
+	float deactivationtime, lineardeactthreshold, angulardeactthreshold;
+
+	/* Scene LoD */
+	short lodflag, pad2;
+	int scehysteresis, pad5;
+
 } GameData;
 
 #define STEREO_NOSTEREO		1
@@ -791,6 +796,9 @@ enum {
 #pragma GCC poison GAME_MAT_TEXFACE
 #endif
 
+/* GameData.lodflag */
+#define SCE_LOD_USE_HYST		(1 << 0)
+
 /* UV Paint */
 #define UV_SCULPT_LOCK_BORDERS				1
 #define UV_SCULPT_ALL_ISLANDS				2
diff --git a/source/blender/makesrna/intern/rna_object.c b/source/blender/makesrna/intern/rna_object.c
index d8aa659b68e..a49388866a6 100644
--- a/source/blender/makesrna/intern/rna_object.c
+++ b/source/blender/makesrna/intern/rna_object.c
@@ -2089,6 +2089,14 @@ static void rna_def_object_lodlevel(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Distance", "Distance to begin using this level of detail");
 	RNA_def_property_update(prop, NC_OBJECT | ND_LOD, "rna_Object_lod_distance_update");
 
+	prop = RNA_def_property(srna, "object_hysteresis_percentage", PROP_INT, PROP_PERCENTAGE);
+	RNA_def_property_int_sdna(prop, NULL, "obhysteresis");
+	RNA_def_property_range(prop, 0, 100);
+	RNA_def_property_ui_range(prop, 0, 100, 10, 1);
+	RNA_def_property_ui_text(prop, "Hysteresis %", "Minimum distance change required to transition to the previous"
+								   " level of detail");
+	RNA_def_property_update(prop, NC_OBJECT | ND_LOD, NULL);
+
 	prop = RNA_def_property(srna, "object", PROP_POINTER, PROP_NONE);
 	RNA_def_property_pointer_sdna(prop, NULL, "source");
 	RNA_def_property_struct_type(prop, "Object");
@@ -2107,6 +2115,11 @@ static void rna_def_object_lodlevel(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Use Material", "Use the material from this object at this level of detail");
 	RNA_def_property_ui_icon(prop, ICON_MATERIAL, 0);
 	RNA_def_property_update(prop, NC_OBJECT | ND_LOD, NULL);
+
+	prop = RNA_def_property(srna, "use_object_hysteresis", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "flags", OB_LOD_USE_HYST);
+	RNA_def_property_ui_text(prop, "Hysteresis Override", "Override LoD Hysteresis scene setting for this Lod Level");
+	RNA_def_property_update(prop, NC_OBJECT | ND_LOD, NULL);
 }
 
 
diff --git a/source/blender/makesrna/intern/rna_scene.c b/source/blender/makesrna/intern/rna_scene.c
index 2e941487e98..a0a0eedcfed 100644
--- a/source/blender/makesrna/intern/rna_scene.c
+++ b/source/blender/makesrna/intern/rna_scene.c
@@ -3886,6 +3886,20 @@ static void rna_def_scene_game_data(BlenderRNA *brna)
 
 	/* Nestled Data  */
 	rna_def_scene_game_recast_data(brna);
+
+	/* LoD */
+	prop = RNA_def_property(srna, "use_scene_hysteresis", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "lodflag", SCE_LOD_USE_HYST);
+	RNA_def_property_ui_text(prop, "Hysteresis", "Use LoD Hysteresis setting for the scene");
+	RNA_def_property_update(prop, NC_SCENE, NULL);
+
+	prop = RNA_def_property(srna, "scene_hysteresis_percentage", PROP_INT, PROP_PERCENTAGE);
+	RNA_def_property_int_sdna(prop, NULL, "scehysteresis");
+	RNA_def_property_range(prop, 0, 100);
+	RNA_def_property_ui_range(prop, 0, 100, 10, 1);
+	RNA_def_property_ui_text(prop, "Hysteresis %", "Minimum distance change required to transition to the previous"
+								   " level of detail");
+	RNA_def_property_update(prop, NC_SCENE, NULL);
 }
 
 static void rna_def_gpu_dof_fx(BlenderRNA *brna)
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);