OVERVIEW
* In 2.7 terminology, all layers and groups are now collection datablocks.
* These collections are nestable, linkable, instanceable, overrideable, ..
which opens up new ways to set up scenes and link + override data.
* Viewport/render visibility and selectability are now a part of the collection
and shared across all view layers and linkable.
* View layers define which subset of the scene collection hierarchy is excluded
for each. For many workflows one view layer can be used, these are more of an
advanced feature now.
OUTLINER
* The outliner now has a "View Layer" display mode instead of "Collections",
which can display the collections and/or objects in the view layer.
* In this display mode, collections can be excluded with the right click menu.
These will then be greyed out and their objects will be excluded.
* To view collections not linked to any scene, the "Blender File" display mode
can be used, with the new filtering option to just see Colleciton datablocks.
* The outliner right click menus for collections and objects were reorganized.
* Drag and drop still needs to be improved. Like before, dragging the icon or
text gives different results, we'll unify this later.
LINKING AND OVERRIDES
* Collections can now be linked into the scene without creating an instance,
with the link/append operator or from the collections view in the outliner.
* Collections can get static overrides with the right click menu in the outliner,
but this is rather unreliable and not clearly communicated at the moment.
* We still need to improve the make override operator to turn collection instances
into collections with overrides directly in the scene.
PERFORMANCE
* We tried to make performance not worse than before and improve it in some
cases. The main thing that's still a bit slower is multiple scenes, we have to
change the layer syncing to only updated affected scenes.
* Collections keep a list of their parent collections for faster incremental
updates in syncing and caching.
* View layer bases are now in a object -> base hash to avoid quadratic time
lookups internally and in API functions like visible_get().
VERSIONING
* Compatibility with 2.7 files should be improved due to the new visibility
controls. Of course users may not want to set up their scenes differently
now to avoid having separate layers and groups.
* Compatibility with 2.8 is mostly there, and was tested on Eevee demo and Hero
files. There's a few things which are know to be not quite compatible, like
nested layer collections inside groups.
* The versioning code for 2.8 files is quite complicated, and isolated behind
#ifdef so it can be removed at the end of the release cycle.
KNOWN ISSUES
* The G-key group operators in the 3D viewport were left mostly as is, they
need to be modified still to fit better.
* Same for the groups panel in the object properties. This needs to be updated
still, or perhaps replaced by something better.
* Collections must all have a unique name. Less restrictive namespacing is to
be done later, we'll have to see how important this is as all objects within
the collections must also have a unique name anyway.
* Full scene copy and delete scene are exactly doing the right thing yet.
Differential Revision: https://developer.blender.org/D3383https://code.blender.org/2018/05/collections-and-groups/
Camera clipping was left to default values, which won't work well for
very large (or small) objects. Now recompute valid clipping start/end
based on boundingbox of rendered data, and final location of camera.
Code was not getting correct boundbox in some cases (group only instancing other groups e.g.), now
compute our own bbox in those cases.
Based on patch by @lichtwerk, but extended the fix to include linked datablocks in some cases
(linked objects in local groups, linked objects in local scene, etc.), this was also broken in existing code.
Reviewers: mont29
Subscribers: duarteframos
Differential Revision: https://developer.blender.org/D2257
Now take into account `dupli_offset` of groups.
Also fixed another issue related to objects renderability, previous code was giving
bad results due to added temp objects to generate previews (camera, lamp...).
Root of the issue was, preview generator was filling ID preview with unsigned int,
when RNA only knows of signed integers (and thus generates a python exception
when converting uint outside of int range)...
Using the brand new and much simple float pixels accessor to PreviewImage now.
Why this was working perfectly OK (it seems...) under Linux, and why error (py exception)
was so badly and misleadingly reported on Windows, remains pitch black mystery to me.
Cannot reproduce the issue here on linux, but have the feeling windows builds are much
more easily broken with referencing bad data from bpy. So here guessing direct loop
over bpy.data.xxx when you do add and remove stuff from said xxx inside the loop
is not a good idea - which seems logical in the end. :P
Not much to add, you can now clear previews from current .blend file, or a set of non-opened files.
Likewise, you can generate previews (for mat/tex, objects, groups, scenes, ...).
