Linking & Overrides (2020 / B3D 2.83)

This tutorial goes through how to link assets and perform overrides in Blender 2.83. Lots of advice is included!
Note that this is designed for pre-university students, so everything is gone over in quite a lot of detail tp avoid mistakes during a very intense event. Tutorial files mentioned at end are not currently available outside of our events unfortunately.
In 2.83 there are still a lot of weaknesses/edge cases/bugs/closets of screaming skeletons; it is a safe assumption they will all be fixed in future versions. Here is a partial list so you can avoid issues at this time:
* Drivers aren't handled correctly when overriding. You can fix this: Override the driver and then switch the variables to the overriden data blocks rather than the linked data block. However, it seems to forget this when you reload the file, making it unworkable.
* If an override is broken by changing the name of a collection/object fixing it is, as far as I can tell, impossible with the current interface. Your best bet is to recreate the override from scratch, copying over any data from the previous (e.g. actions within the NLA). Interestingly, it can break in two ways: Content vanishes, or it just keeps going, working as before but with the link no longer updating from the source file. I have been unable to determine the reason why it goes one way/the other, though expect it's down to dependencies that have not been overriden and if it can still find them or not.
* Additive changes to the source file don't always get picked up by overrides. It seems to work by keeping two copies and taking the difference to work out what has/hasn't been overridden when looking at lists. Because there is no "deleted item" in the overriden list this is fundamentally broken - it can't tell if an extra item in the source list is new or deleted. No tool to fix other than recreating the override as far as I can tell.
* Not all modifiers are handled correctly: Sometimes you need to manually correct references to other objects within overriden modifiers.
* Latices do not work with duplicate characters: They randomly snap backwards and forwards between each other. Would guess the modifier stores a name and finds a different lattice each time through the dep graph! So no swarms of cute wide eyed cartoon characters consuming their prey at this time:-(
Note that I have not had as much time as I would like to experiment, and keep learning new things as we run events!

[@DodaGarcia]

The background scene thing blew my mind completely

[@bryanroot]

Thank You!!! I have been trying to understand this stuff by reading the Blender Manual. You make it so much easier to understand.

[@patrickpope4655]

Most detail I could find on linking is here. It is clearly organized and communicated. Great job! I hope you make more videos on rarely covered Blender topics like this.

[@jeffdahl5298]

Superb tutorial covering a lot of ground very efficiently and accurately. Neither chatty nor repetitive which is appreciated. I watch at 1.25x speed, otherwise it's too slow.

[@miquelrosell5498]

This tutorial is soooo goood. Thanks for the clear explanations!

[@annamariviita1438]

Great tutorial! Asiaa...as we say in Finland. Efficient and accurate, no fancy stuff. I will immediately subscribe your channel. :-D

[@dodaexploda]

This is absolutely amazing content. Such clear info besides the fiver other videos that were basically "select link from the menu and select a collection". Thank you very much!!!!!

[@johnwalkerlee3465]

I love this tutorial, so Zen, but so jam packed full of useful info.

[@lln6123]

Very informative Video, thanks alot

[@juancarlosaragon723]

this tutorial is great, i didn´t find this in anyother place, but i have a question... if i need link the freestyle compo settings what is the way?

[@piersregan7586]

Thank you.

Thank you, very informative and useful. Keep up the good work !

[@DodaGarcia]

Anyone else terrified by the giant ant or just me

[@skilldownloder3137]

Thank you! That was very helpful : )

[@myztazynizta]

I don't do characters. Everything I've tried with library overrides has failed or been buggy. FYI you don't have to place things at the world origin for the picot point of the linked collection to be in a good place. You can put the 3d cursor anywhere and tell the collection to use that location as the pivot point for all instances of the collection.

[@mortasm1]

top info right here!!

[@berni85]

Is there any way to update/reload/refresh linked collection in blender 3.x ??? Reloading project file not working, and i can't find any other way in Outliner nad Blender file info to refresh modified collection. Please help

[@TomSFHaines]

So linking keeps references to data from the source file, with deltas when it can, but some bits of information are just copied over, most obviously the hierarchy of objects and what that hierarchy contains/doesn't contain. Reloading the file just recalculates the linking, but won't do anything about the information that has been copied. In current versions you can right click on a linked object and there is a "Library Override" menu, with a "Troubleshoot" submenu under which you will find a "Resync" option: that recopies over the hierarchy structure and will make new objects appear/old ones disappear. Save before trying in case it goes wrong! If the issue is a data block attached to a specific object is not updating then you can reset that under the reset menu, but you may need to identify the exact data block and you will lose any edits on that data block. Can be a bit of trial and error at times, but in current versions is actually reasonably polished and it works well for most cases. Sometimes you need to bring up the "Blender File" view in the outliner to get a fine grained view of the Blender file so you can select the exact thing you need.

[@PurpleArkStudio]

You saved me!!

[@XoioDe]

Thank you so much for the thorough explanation. ONE Question: Is there a way to override multiple objects at once?

[@TomSFHaines]

As far as I can tell, no - you have to do them one at a time. Can't be entirely sure that function isn't hidden somewhere though, and you could write code to do it. If you have so many characters that's an inconvenience you're probably entering Alembic/caching territory though, so doubt that's ever a serious problem!

[@XoioDe]

@@TomSFHaines Thanks. I am trying first time Blender in Production and linking a lot of assets from a database ... it's quite a pain if you have a "static mesh" consisting of multiple objects and can't move them.

[@TomSFHaines]

@@XoioDe If you link a collection that contains lots of different objects (e.g. a set layout) you can override it and then move the individual objects around. But if it's one mesh, yeah, you're stuck. With planning you can rig shape keys, drivers or modifiers etc. to have the control you need over a single mesh, but that gets very, very tedious. Probably best to go back to the assets and separate them into different objects, then if there are reused layouts organise them in a hierarchy of collections ready for linking. Building out a pipeline does take time, and usually has to be iterative as you find problems you weren't expecting, so good luck!

[@XoioDe]

@@TomSFHaines Thanks, Tom. Appreciated - will look further into it. Edit: Combining it into a collection and then override is a great way to do it! Wonder, why nobody mentioned this anywhere else, thanks!

[@jkartz92]

how to access modifiers in the overriden character asset?

[@TomSFHaines]

At the time the video was recorded you could edit modifiers of an overridden object and it kinda worked, but there were some bugs that meant it wasn't really safe for production. It seems to have got a lot better now, but I need to test it out and check it's production ready. Inevitably going to need to record a new version of this video at some point - few details are now out of date.

[@SanPerroud]

That's great info, thank you. Quick question: If the character comes with animation is it possible to delete the keyframes in the overridden version? I tried and it ignores the delete command. Or you need to delete keyframes in the original?

[@3Damistudios]

You never include animation directly on a character, so would recommend deleting. Overrides don't support editing animation yet: you can create the override, though it's quite well hidden, but it doesn't survive a save then reload. You can still link animation however, via "actions" (that does mean learning the basics of the non-linear animation editor), so if you have something like a walk cycle turn it into an action, click the little fake user shield so it is not going to be deleted and then remove it from the character, so it doesn't come across when linked. You can then link the action separately into shots when you want to use it, applying it with the NLA.

[@dannyaustin84]

I've been looking for a way to library override materials from linked scenes.. so far I haven't been able to do it. Is this possible? Did I miss it?

[@TomSFHaines]

It's right on the edge of what is supported right now! (2.91, which has changed some details given in above tutorial) There are two places you can set the material in Blender: either at the mesh (data) or at the object - that's what that drop down just below the material list is for. You can't override meshes at all, but you can override objects, which means that if you assign the materials to the object that works. Need to override the object to do so, but that now happens automatically when creating the override of a linked collection. Back with 2.83 for which I made the above video it was unstable: Worked, but didn't survive saving and then reloading the file. Now it appears to stick, so it is usable. This only works for complete material replacement however: Editing the nodes of an overridden material doesn't work, and material drivers are broken.

[@lwd4032]

what is the advantage of linking collection instead that object?

[@TomSFHaines]

It's in part convention due to history, as previously collections were the only real choice, but now you'll get away with linking an object. Still, collections have several advantages which mean I would almost always choose them: 1) You can move/rotate/scale a collection instance, but not a linked object unless you override it first. Which you can do, but overriding adds computation and complexity that doesn't exist with the collection instances - will slow Blender down a lot if you're trying to dress an entire set that way. 2) A collection gives you more flexibility - you can replace a single object with several for instance, or realise that you need to rig a prop. This can matter a lot when things get heavy, as you can have two versions of a prop in a collection, with a simple version that's only visible in the viewport and a complex one that's only visible when rendering. 3) Because everyone uses collections most of the time it's the more stable code path - you're less likely to bump into bugs doing it that way!

[@mrmacnoobster]

Working with large rigged assets with overrides is absolutely horrid. Have multiple mechanical assemblies with anywhere from 2000 to 5000 objects in a single rig. Reloading a scene with them linked in can take hours

[@TomSFHaines]

Sorry, missed this message, and probably replying too late, but just in case it is useful: large numbers of objects are slow because they have to be processed one at a time and because of how OpenGL works (should get better when Blender supports Vulkan). The trick is to join them, ideally down to a few Blender objects, and then rig the individual parts within each object via armatures/weight groups: that's orders of magnitude faster! Reloading speed was known to be slow - I believe it has been optimised now and hence should be much better.

[@mrmacnoobster]

@@TomSFHaines Working on large engineering projects, in my case at least, merging objects would be multiple days of work and result in updates taking way to long further down the road. It's mental how we can't just override the Rig, without touching anything else. In many scenarios there is absolutely no need for a Animator to do anything with the meshes in the animation file.

[@TomSFHaines]

@@mrmacnoobster Ah, yeah - no good solution to that problem:-/ Could possibly automate the merging with some Python scripts, but now you've got some Python scripts and a pipeline to maintain as well! Would only make sense if working inside a large company.