I am trying to obtain a p-map (position map) in 2.80. Since the only way I found is to have a different material with a Geometry/Position node as input, I need to switch between materials (the "real material" and the p-map material). Since I would like to render them in the same rendering (it is part of an animation and I need both images for each frame), I was looking for a trick. The first trick I found is to use a material override in a new scene. But Blender 2.80 does not (yet?) have a material override (doh!). So I tried to do the following: I created a new scene (SceneForPMap) and I set a new material, in that scene for all the objects, hoping that the object material is a per-scene setting. Then, I added a new RenderLayer input in the compositor and put its output in a FileOutput node.

But I found a set of very hard-to-understand problems:

  1. There is a compositor configuration for each scene... I would expect to have a compositor per Blender file, since it can have as input a render of a scene (the compositor seems to be more "high-level" than a scene).
  2. The material is not per-scene, if I change the material of an object (with a scene selected in the top drop-down select box), it is the same in all the scenes (changing the scene in the top drop-down select box)... but more confusing, if I render (F12) I obtain a material for the normal scene RenderLayer and the p-map material for the RenderLayer of SceneForPMap.

I am confused, maybe I am doing something wrong, or I misunderstood something else.

  • $\begingroup$ The Render Layers node allows you to directly render from a different scene of the same faile without file outputs. This may also help blender.stackexchange.com/questions/55233/… $\endgroup$ Jan 11 '19 at 18:21
  • $\begingroup$ Also see blender.stackexchange.com/questions/93043/… $\endgroup$ Jan 11 '19 at 18:22
  • $\begingroup$ So, if I understand correctly, there is a compositor configuration for each scene, where the "default" RenderLayer node renders the current scene, but it is possible to composite this scene with other scenes. It is a little bit misleading for me, since in this way, I could have in a scene the composite of other two scenes (and not the current one). $\endgroup$
    – MadMage
    Jan 14 '19 at 8:57
  • $\begingroup$ It is still not clear for me the other link: materials and scenes. As far as I understand, the link between them is scene -> object -> material, since I have the same objects (referenced) in the two scenes, they also have the same material: if I change the material in one scene, I am also changing it in the other scene. So it seems to be a bug the fact that rendering the first scene shows the previous material (maybe it is cached and the cache is not properly invalidated?). $\endgroup$
    – MadMage
    Jan 14 '19 at 8:59

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