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

2 files changed, 21 insertions, 0 deletions

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) {