Adding/removing objects from animation

Aim: to have objects disappear and reappear during 3D and 2D animation. Currently my movies just have simple slide-in and fade-out actions for text and flat images, plus a 3D rotating logo, overall a bit like fancy PowerPoint shows.

Four related questions: (links to docs or tuts welcome!)

  1. What is the approved technique for making an object fade-out or -in?

  2. This provoked the question: can I have a single RGB ‘background’ node or property and reference it across several different text materials?
    I expected the Alpha property in the BSDF to control transparency but it just works as an on/off. So I currently use a mixer node which gives text a nice fade-in/fade-out between keyframes. It was tricky getting the text to fade out exactly against the background, if does not quite match a ‘ghost’ remains. Right now I clumsily fade out by mixing each to its own RGB node which is set to the default background level ( #404040).

  3. What is the approved method for adding and removing objects from the ‘stage’ during an animation?
    Currently when an object fades out, I park it off-stage (outside the camera view), and bring in others on-stage using one-frame move transitions, and then fade them in. The scene is getting bit cluttered. I tried animate the ‘visibility’ of an object like in the Scene tree UI view or is an object’s lifetime always the same as it’s scene’s lifetime?

  4. (related to #1) What it the generic method for making an animated ‘variable’ globally accessible across several different nodes? Is this done with a DRVER?

Thanks. I will try to collate the answers and feed them back into Blender Docs.

There’s no such thing as “approved technique” lol. What you do depends on what you want. If you want to fade out, then animated alpha makes sense. If you don’t, then keyframing visibility makes sense. Moving things about between frames works fine too. Only thing to worry about is if you ever retime your animation, but you could use constant interpolation loc keyframes to take care of that too.

You can make a cross-material property most easily by sticking it in a node group and then copy/pasting that node group between materials. Node groups are linked until you unlink them, so changing what’s inside the node group (incl. animating it) affects all materials using that node group.

Yes, you can use a driver to control multiple materials too, but it’s not as easy as just using a shared node group. While you can create custom properties I generally just use the positions of empties as “global variables.”

Alpha in BSDFs should control transparency, not be on/off. But if you’re Eevee rendering with alpha clip for materials, it’ll only be on/off-- you’ll want alpha blend or hashed. Probably hashed, considering the complexity of text objects. Shadows can’t do alpha blend. Workbench renders only ever do alpha clip.

If your scene is cluttered, start using collections and collection visibility.

Hi thanks for the reply :slight_smile: Yes I used ‘approved’ as shorthand for you-know-what: the insider’s well-worn methods - ‘Duh, you mean you don’t know about x???’

Animating Alpha - my prior experience indicated this should have worked, but I didn’t know about that Eevee gotcha tnx.

Clutter - is there somewhere to stash characters until they are needed later in a scene?
e.g. I have several book-cover images-as-planes waiting in the wings to march on-stage in sequence. It helps the timing for them to all start from the same ‘ready’ position just before their action commences, but that means they are all stacked on top of each other at the start. I will look into layers, maybe if each is on a layer that is the solution.

Constant interpolation loc keyframe? A keyframe that sets (location) value(s) that remain steady until until a later keyframe makes a change? I’ll note that - might be handy, tnx.

Node Groups ? Never heard of them but I do now :slight_smile: tnx. That is why pasting nodes just ended up with a lot of individual nodes, all needing individual care.

If you use an empty how do you connect it to its follower? Do you use it as an input for a Driver?

Anyway I inspired myself to look at the NLE (the Animation non-linear editor) to automate the visibility of layers. I also revised a bunch of tut videos. So I understand more ways to link dynamic actions between objects, using a driver, a bone, or one of the Follow modifiers.
Finally: Can object visibility be automated more directly? If I animate the Visibility property of an object I can put in a couple of keyframes with visibility ON, but when I set visibility OFF on the property sheet the cube also disappears from the timeline and NE editor windows, and any further ‘I’ or mouse-click keyframe commands are ignored, even though the now invisible cube is still selected in the Collection tree.
I’ll look into Layers, maybe the visibility of each layer can be animated.

X = -10000 seems like a reasonable place. Name appropriately and select via outliner.

If using as a global variable, yeah, probably, although I’m sure there are occasional exceptions where it’s easier to use as a constraint target or something.

I don’t think you can animate the visibility of entire collections/layers, just objects. But I haven’t played with it much, that might be out of date. Collections are mostly an organizational technique, not a rendering technique (although I do tend to put non-rendering meshes on a single non-rendering collection, just in case I forget to disable “display in renders” on some of them.)

Consider using drivers to animate visibility, consider using other objects to animate hidden objects (objects like an empty parent or an armature, which won’t be displayed in renders anyways).

Thanks again

As I said, I can’t get the Visibility to animate usefully, but as I can’t get it to accept keyframes for the object when it is OFF, it can only be used to turn the Visibility OFF!
I will try to animate a dummy object as a switch, then connect it to the objects’ visibility property in some way.
Maybe a group’s visibility can be animated, then I can add objects to it.
I looked around the UI and the Manual for Layers but can’t yet see where to ‘ADD New Layer’ or ‘Move Object to layer x’.
Maybe I just need to add my various item types to separate scenes that are then composited into my little show.

You keep talking about layers. Are you using Blender 2.79x? If so, layers and collections don’t work exactly the same.

You can move an object to a collection by selecting the object and hitting ‘m’. If you look at the dropdown, there’s an option for “move to new collection”.

Sorry, I’m on 2.82.
OK so the docs might need updating. I’ll check out its release notes wiki and Dev forum, see what there is about this. I joined those over some early 2.8 Mac and doc issues.
For the moment I’ll get the Alpha working with your suggested alpha-blend settings - just have to find out where they are!

With eevee set as rendering engine, properties/material/settings.

OK got it!
I’m actually on 2.90.1 - don’t know where 2.82 came from!
Thanks for the help. What do you work on mostly?

I work on character models. I’m not good enough yet though. It’s because I’m not a great artist. I finished a model, I got depressed because it still didn’t meet my standards, I procrastinate working on new things by helping people fix their technical problems (which I’m good at.)

Hey, you sound like me! I was jolted out of this impasse by my wife Gill saying,”Hey, you can draw, can you do some puzzles for my magazine?”
So now, three issues in, Gill is a ‘published author’ with ISBN nunbers and all, and that makes me, officially, a ‘published illustrator’!

So things can move fast once you find a niche that wants YOUR style of work,
however you achieve it. So all of you newbies, put it out there - not a copy of something familiar, but something never seen before, that’s what buyers need to grab their readers attention.
After all, the ‘primitive’ Beavis and Squarepants animations took off, because of the content, not the artwork skills.
Remember that original work adds value to a company’s IP portfolio.

Now I’m off to upload my portfolio :slight_smile:

Cheers and thanks for the tech support, helped me get it out the door.
Simon A
(Inkscape, Affinity Photo, Blender, Intuos pen, paper n pencil, camera, felt pen on whiteboard…)