Fix T63411: Crash adding meta-ball with a small radius

Change how the radius, changing the size of meta plane, sphere & cube.

Previously the size of these primitives would be kept the same,
with only the radius outside the primitive being scaled.

This led to small scale adding a lot of polygons instead
of scaling the primitive down as users would expect.

Also change behavior not to change the resolution when adding
to an existing meta-ball.

3 files changed, 21 insertions, 7 deletions

diff --git a/source/blender/editors/include/ED_mball.h b/source/blender/editors/include/ED_mball.h
index 938d1059f90..5c2106b934c 100644
--- a/source/blender/editors/include/ED_mball.h
+++ b/source/blender/editors/include/ED_mball.h
@@ -38,8 +38,12 @@ void ED_operatortypes_metaball(void);
 void ED_operatormacros_metaball(void);
 void ED_keymap_metaball(struct wmKeyConfig *keyconf);
 
-struct MetaElem *ED_mball_add_primitive(
-    struct bContext *C, struct Object *obedit, float mat[4][4], float dia, int type);
+struct MetaElem *ED_mball_add_primitive(struct bContext *C,
+                                        struct Object *obedit,
+                                        bool obedit_is_new,
+                                        float mat[4][4],
+                                        float dia,
+                                        int type);
 
 bool ED_mball_select_pick(
     struct bContext *C, const int mval[2], bool extend, bool deselect, bool toggle);
diff --git a/source/blender/editors/metaball/mball_edit.c b/source/blender/editors/metaball/mball_edit.c
index a25175510cd..386fa1efa95 100644
--- a/source/blender/editors/metaball/mball_edit.c
+++ b/source/blender/editors/metaball/mball_edit.c
@@ -93,9 +93,11 @@ void ED_mball_editmball_load(Object *UNUSED(obedit))
 {
 }
 
-/* Add metaelem primitive to metaball object (which is in edit mode) */
+/**
+ * Add meta-element primitive to meta-ball object (which is in edit mode).
+ */
 MetaElem *ED_mball_add_primitive(
-    bContext *UNUSED(C), Object *obedit, float mat[4][4], float dia, int type)
+    bContext *UNUSED(C), Object *obedit, bool obedit_is_new, float mat[4][4], float dia, int type)
 {
   MetaBall *mball = (MetaBall *)obedit->data;
   MetaElem *ml;
@@ -109,9 +111,17 @@ MetaElem *ED_mball_add_primitive(
 
   ml = BKE_mball_element_add(mball, type);
   ml->rad *= dia;
-  mball->wiresize *= dia;
-  mball->rendersize *= dia;
+
+  if (obedit_is_new) {
+    mball->wiresize *= dia;
+    mball->rendersize *= dia;
+  }
   copy_v3_v3(&ml->x, mat[3]);
+  /* MB_ELIPSOID works differently (intentional?). Whatever the case,
+   * on testing this needs to be skipped otherwise it doesn't behave like other types. */
+  if (type != MB_ELIPSOID) {
+    mul_v3_fl(&ml->expx, dia);
+  }
 
   ml->flag |= SELECT;
   mball->lastelem = ml;
diff --git a/source/blender/editors/object/object_add.c b/source/blender/editors/object/object_add.c
index 50f85545c19..653e9d39eca 100644
--- a/source/blender/editors/object/object_add.c
+++ b/source/blender/editors/object/object_add.c
@@ -860,7 +860,7 @@ static int object_metaball_add_exec(bContext *C, wmOperator *op)
    * we want to pass in 1 so other values such as resolution are scaled by 1.0. */
   dia = RNA_float_get(op->ptr, "radius") / 2;
 
-  ED_mball_add_primitive(C, obedit, mat, dia, RNA_enum_get(op->ptr, "type"));
+  ED_mball_add_primitive(C, obedit, newob, mat, dia, RNA_enum_get(op->ptr, "type"));
 
   /* userdef */
   if (newob && !enter_editmode) {