UI/Assets: Support generating object preview images

Object previews are really helpful for visual data-block selection, like asset
browsing. Having them be generative should also be quite handy and should work
well enough in many, if not most cases.

What this does is simple:
* Place the object (actually a deep copy of it, for thread safety) in a virtual
  .blend into an empty scene/view-layer.
* Add a camera, point it towards the front of the object, assuming that means
  pointing towards its +Y axis.
* Use "Camera Fit Frame to Selected" logic to put the object into frame.
* Create a threaded off-screen render.

Of course, such an automatic preview will not work in all situations. E.g. it
currently does a bad job capturing a single plane. We could add options for
more advanced automatic previews, but probably custom previews is more
important, which I committed already (812ea9184221).

Part of the first Asset Browser milestone. Check the #asset_browser_milestone_1
project milestone on developer.blender.org.

Reviewed as part of https://developer.blender.org/D9719.
Reviewed by: Bastien Montagne, Brecht Van Lommel

1 files changed, 35 insertions, 0 deletions

diff --git a/source/blender/editors/space_view3d/view3d_utils.c b/source/blender/editors/space_view3d/view3d_utils.c
index 1be9bd27c7a..2b7b8255068 100644
--- a/source/blender/editors/space_view3d/view3d_utils.c
+++ b/source/blender/editors/space_view3d/view3d_utils.c
@@ -1620,6 +1620,41 @@ void ED_view3d_to_object(const Depsgraph *depsgraph,
   BKE_object_apply_mat4_ex(ob, mat, ob_eval->parent, ob_eval->parentinv, true);
 }
 
+bool ED_view3d_camera_to_view_selected(struct Main *bmain,
+                                       Depsgraph *depsgraph,
+                                       const Scene *scene,
+                                       Object *camera_ob)
+{
+  Object *camera_ob_eval = DEG_get_evaluated_object(depsgraph, camera_ob);
+  float co[3]; /* the new location to apply */
+  float scale; /* only for ortho cameras */
+
+  if (BKE_camera_view_frame_fit_to_scene(depsgraph, scene, camera_ob_eval, co, &scale)) {
+    ObjectTfmProtectedChannels obtfm;
+    float obmat_new[4][4];
+
+    if ((camera_ob_eval->type == OB_CAMERA) &&
+        (((Camera *)camera_ob_eval->data)->type == CAM_ORTHO)) {
+      ((Camera *)camera_ob->data)->ortho_scale = scale;
+    }
+
+    copy_m4_m4(obmat_new, camera_ob_eval->obmat);
+    copy_v3_v3(obmat_new[3], co);
+
+    /* only touch location */
+    BKE_object_tfm_protected_backup(camera_ob, &obtfm);
+    BKE_object_apply_mat4(camera_ob, obmat_new, true, true);
+    BKE_object_tfm_protected_restore(camera_ob, &obtfm, OB_LOCK_SCALE | OB_LOCK_ROT4D);
+
+    /* notifiers */
+    DEG_id_tag_update_ex(bmain, &camera_ob->id, ID_RECALC_TRANSFORM);
+
+    return true;
+  }
+
+  return false;
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */