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, 10 insertions, 0 deletions

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