RNA: Cleanup PointerRNA struct

The old layout of `PointerRNA` was confusing for historic reasons:
```
typedef struct PointerRNA {
  struct {
    void *data;
  } id;

  struct StructRNA *type;
  void *data;
} PointerRNA;
```

This patch updates it to:
```
typedef struct PointerRNA {
  struct ID *owner_id;
  struct StructRNA *type;
  void *data;
} PointerRNA;
```

Throughout the code base `id.data` was replaced with `owner_id`.
Furthermore, many explicit pointer type casts were added which
were implicit before. Some type casts to `ID *` were removed.

Reviewers: brecht, campbellbarton

Differential Revision: https://developer.blender.org/D5558

1 files changed, 3 insertions, 3 deletions

diff --git a/source/blender/makesrna/intern/rna_meta.c b/source/blender/makesrna/intern/rna_meta.c
index 743bac2b709..451bdda45f5 100644
--- a/source/blender/makesrna/intern/rna_meta.c
+++ b/source/blender/makesrna/intern/rna_meta.c
@@ -89,7 +89,7 @@ static void rna_Meta_texspace_size_set(PointerRNA *ptr, const float *values)
 
 static void rna_MetaBall_update_data(Main *bmain, Scene *scene, PointerRNA *ptr)
 {
-  MetaBall *mb = ptr->id.data;
+  MetaBall *mb = (MetaBall *)ptr->owner_id;
   Object *ob;
 
   /* cheating way for importers to avoid slow updates */
@@ -158,13 +158,13 @@ static void rna_MetaBall_elements_clear(MetaBall *mb)
 
 static bool rna_Meta_is_editmode_get(PointerRNA *ptr)
 {
-  MetaBall *mb = ptr->id.data;
+  MetaBall *mb = (MetaBall *)ptr->owner_id;
   return (mb->editelems != NULL);
 }
 
 static char *rna_MetaElement_path(PointerRNA *ptr)
 {
-  MetaBall *mb = ptr->id.data;
+  MetaBall *mb = (MetaBall *)ptr->owner_id;
   MetaElem *ml = ptr->data;
   int index = -1;