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

1 files changed, 41 insertions, 1 deletions

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);
 	}
 }