Fix T85051: Add bisect distance as a parameter to the mirror modifier

The `bisect_distance` in the mirror modifier was hard-coded to `0.001`.
This would result in some unexpected behavior like vertices close
to the mirror plane being deleted or merged.

The fix now adds a parameter to the mirror modifier to expose the
bisect distance to the user. The default is set to the previous
hard-coded value to not "change" previous files.

Ref D10201

1 files changed, 13 insertions, 0 deletions

diff --git a/source/blender/blenloader/intern/versioning_290.c b/source/blender/blenloader/intern/versioning_290.c
index 916c4bf0cad..fe8e46e8928 100644
--- a/source/blender/blenloader/intern/versioning_290.c
+++ b/source/blender/blenloader/intern/versioning_290.c
@@ -2059,6 +2059,19 @@ void blo_do_versions_290(FileData *fd, Library *UNUSED(lib), Main *bmain)
     }
   }
 
+  /* Set default value for the new bisect_threshold parameter in the mirror modifier. */
+  if (!MAIN_VERSION_ATLEAST(bmain, 293, 19)) {
+    LISTBASE_FOREACH (Object *, ob, &bmain->objects) {
+      LISTBASE_FOREACH (ModifierData *, md, &ob->modifiers) {
+        if (md->type == eModifierType_Mirror) {
+          MirrorModifierData *mmd = (MirrorModifierData *)md;
+          /* This was the previous hard-coded value. */
+          mmd->bisect_threshold = 0.001f;
+        }
+      }
+    }
+  }
+
   /**
    * Versioning code until next subversion bump goes here.
    *