How can I change the opacity (alpha) to multiple materials at once?

Question

I have this system of pipes I would like to fade into the scene, but since every pipe has its own material I would need to create keyframes for every single material in there, and there's around 50 of them so it take a considerable amount of time to animate each one separately.

Is there a way to animate them (fade in with alpha going from 0 > 100) all together? Or at least copy and paste the keyframes from one material to the other?

The pipe system

Answer 1

ok, here is a basic python script, which does what you want.

PREQUISITE:

1. You have a collection named "Automatic" where all objects are in for which you want that behaviour.

2. Each of your materials have a Principled BSDF and it is named that way (not renamed)

works for Cycles and Eevee.

    import bpy

    index = bpy.data.collections.find('Automatic')
    coll = bpy.data.collections[index]
    scene = bpy.context.scene

    for eachObject in coll.objects:
    
        for eachMat in eachObject.data.materials:
        
            nodes = eachMat.node_tree.nodes
        
            pb = nodes.get('Principled BSDF')
            eachMat.blend_method = 'HASHED'

            if pb:            
                pb.inputs[19].default_value = 0
            
         pb.inputs[19].keyframe_insert(data_path="default_value", frame=0) # do inset this to the line above
                pb.inputs[19].default_value = 1
            
          
         pb.inputs[19].keyframe_insert(data_path="default_value", frame=100) # do inset this to the line above
            
                print ("set for ", eachMat)
        
  

Answer 2

There are several ways to do this. One technique that is often overlooked is to use a Value node contained in a node group. This works because if you change a value inside a node group, it changes in every material that uses that node group. It's a bit of work in your case, because you have to add the node group to every material, but here's an example.

1. Initial setup

   • Add a Value node to any one of your materials.
   • Deselect all of the other nodes in that material and select the value node.
   • Type Ctrl–G to create a node group.

At this point, your node editor will look something like this:

* Enter <kbd>Tab</kbd> to close the node group:

Now when you have the group selected, typing Tab will toggle whether it is open or closed.

• Open the sidebar in the node editor and open the Properties panel. In it, you'll see an entry for the Node group's name. Change it to something meaningful. I picked "Animation" for the example.

• Connect the Value output of the NodeGroup to the Alpha input of your BSDF node.

• Now you can add the Nodegroup to every material that you want animated by typing A and selecting your name from the Group submenu:

2. Animation

• Pick any material, select the node group and open it.
• Move to frame 1 on the time line, set the value to 0, and keyframe it. (You can keyframe the value of an input just like any other field. Set it to 0, hover over it, right click and pick Insert Keyframe.
• Move to the frame where you want the fade to start and keyframe the value
• Move to the frame where you want full visibility. Set the value to 1. Keyframe it.