Three questions:
1. I have only ever ticked the holdout option in the outliner, holdout as a node is new to me; my first question is: do they (node and outliner) perform the same function?
2. Ok, my second question comes from the perspective e of an updated version of Blender and I believe would be better asked in the Compositing Course, nevertheless: When using nodes to hold out on an object per object basis, is it better to composite them back in simply with an Alpha Over or should one use either the Disjoint or Conjoint operations?
3. Can the Holdout Node be a way to manually apply occlusion culling on our renders?
Hi Jon,
As to 1. Holdout in the Outliner is per Object (/Collection), a Holdout Node is per Material.
As for question 2. I don't know, I'd try the 3 different Options and see which does what I want (the Tooltips might also be of some help).
And 3. I don't know what you mean by Occlusion Culling.
I expect that someone else will be able to better help you here.
1. Oh! It's per material. Ok now it makes perfect sense.
2. I'll try the different options out.
3. Kinda like camera culling, as in if it is not visible the Camera's view, Blender doesn't have to calculate it. But by Occlusion Culling I mean if soenthing is within the Camera's view but not visible because something else is in the way, if you have an object in front of another object, then you cull the occluded object, meaning, Blender wouldn't waste resources calculating the object that's behind. A quick silly for instance I was imagining, If I have nesting dolls I could apply the holdout node to the first internal doll which is not yet visible, and basically mask out every other doll, which also isn't visible yet.
P.S
Thanks for always answering my questions. The courses are already fantastic, but these small clarifications make 'em even better and more fun.
Hm,
I am not 100% sure, but I think Occlusion Culling like you mean already happens automatically in Cycles. That is, for the Russian Doll example.
If an Object is behind an other, it might have some contribution, via Indirect Bounces, to the Lighting, or be visible in Reflections.
You'd probably be better off using EEVEE, if you want something like that.
1. The both work the same as far as the final output. In high poly scenes, you break up the scenes into scenes, and if you don't have the system resource you then break it up into separate files. So you may have a background file/scene, the animation file/scene, and a foreground/environment effect file/scene. In the animation file/scene, you would use simple objects with the hold material, because that uses less resource than using the holdout collection. Although it is very small difference if you have a compatible GPU; however, if you use only CPU rendering it makes a noticeable difference when rendering an animation. Remember a fraction of a second on a single image adds up when you're doing 24, 25, 30, or more frames per second.
2. Alpha over is the normal way.
3. It can be used to achieve this affect, but it's not necessary for occlusion culling since blender already uses this method instead of Frustum culling. However Blender does use Frustum culling for the lights in eevee. This may have been changed in eevee next(Latest version)