LibOverride: Add full support for camera's background images.

Add support for adding (inserting) new background images into an
override of a linked Camera ID.

Request from the Blender studio.

This ended up being more involved than expected as it uncovered some
latent issues with existing background images code. Noticiably, a new
`BKE_camera_background_image_copy` had to be added to handle copying
of background images in a proper, generic ID-management way.

1 files changed, 11 insertions, 0 deletions

diff --git a/source/blender/editors/space_view3d/view3d_edit.c b/source/blender/editors/space_view3d/view3d_edit.c
index fb5e7e58d33..a65e9a8d506 100644
--- a/source/blender/editors/space_view3d/view3d_edit.c
+++ b/source/blender/editors/space_view3d/view3d_edit.c
@@ -631,6 +631,17 @@ static int background_image_remove_exec(bContext *C, wmOperator *op)
   CameraBGImage *bgpic_rem = BLI_findlink(&cam->bg_images, index);
 
   if (bgpic_rem) {
+    if (ID_IS_OVERRIDE_LIBRARY(cam) &&
+        (bgpic_rem->flag & CAM_BGIMG_FLAG_OVERRIDE_LIBRARY_LOCAL) == 0) {
+      BKE_reportf(op->reports,
+                  RPT_WARNING,
+                  "Cannot remove background image %d from camera '%s', as it is from the linked "
+                  "reference data",
+                  index,
+                  cam->id.name + 2);
+      return OPERATOR_CANCELLED;
+    }
+
     id_us_min((ID *)bgpic_rem->ima);
     id_us_min((ID *)bgpic_rem->clip);