Fade in action applicable to all objects (in cycles)

Question

I am trying to make a schematic video about assembling a machine. For a lot of objects (bolts, etc...) I use the same delta location action, so they get assembled in their position. This allows me to use the NLA editor, to make almost all the animations.

The problem is when I try to fade in & fade out objects. Loc, rot & scale works well, because all objects share these properties. But transparency depends on the material.

I've tried to have all materials end with a mix node connected to a transparent shader. So with the 'Fac' slider I can animate the fade. But the result action can't be shared between different objects, as they have different materials.

So, is there any visibility property of object I can animate? This would be great for motion graphics too.

Thanks

Answer 1

I do this very often doing edu videos, and do it this way:

Use object info node -object index to animate per-object visibility. I animate values 0-100 for the 'pass index' property of the object, then multiply these by 0.01 and use resulting value to mix transparent and any other shader

Answer 2

You could use a node group to do this:

1. Add a mix shader and create a new node group by selecting it and pressing CtrlG

2. Add a transparent shader to the node group:

   

3. Add this node group at the end of all the materials you want to simultaneously fade in/out:

   

   This process can be made a little bit faster with copy and paste:

   1. Select the node group and press CtrlC

   2. Select each object/material and press CtrlV to paste the node group.

4. Adjusting the Factor of the mix node inside the node group will set it for all instances of the node group

With the factor set at .5 and .8 (click for larger image):

Answer 3

You could move all objects, that are to be faded in simultanously, to the same scene layer. Then setup a render layer that only renders this scene layer. In the compositor you can easily fade in this render layer.