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I want to have an object come out of a surface as if the surface is a portal or something similar, like Mary Poppins' bag.

How can I accomplish this. My method was to surround the object with a boolean difference box and animate it moving out of the box. However, this has some rendering glitches when I try to animate it.

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  • $\begingroup$ Do you want the "portal" surface to be visible? $\endgroup$
    – gandalf3
    Oct 27, 2014 at 3:07
  • $\begingroup$ Not necessarily. The main effect I am looking for is something appearing out of nowhere. If I need a surface I guess I can place "false" portal. $\endgroup$
    – AGibbons
    Oct 27, 2014 at 4:23
  • $\begingroup$ Related: blender.stackexchange.com/q/7793/599 $\endgroup$
    – gandalf3
    Oct 27, 2014 at 6:47

1 Answer 1

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If both objects are manifold and don't have any self-intersections, the boolean method should work.

However, booleans are sometimes finicky for no reason, so here's another approach:

  1. Move the object you want to appear to a empty layer (e.g. layer 2), keeping the rest of the scene on layer 1

  2. Make a bounding cube as if you were going to use a boolean modifier, but instead give it a holdout material which is only visible to the camera (so that it doesn't cast a shadow):

    enter image description here

  3. Create a new renderlayer and set it to only layer 2. Also change the existing renderlayer to only layer 1:

    enter image description here

  4. Enable Transparent in Render settings > Film

  5. Set up the composite nodes

    enter image description here

Result:

The shadow is an obvious limitation, but I can't think of a good workaround aside from just removing the shadow completely..

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  • $\begingroup$ This seems like an interesting technique. I will try it. Regarding the boolean modifier, I had rendering issues at specific frames, I'm guessing because some faces were overlapping or something. $\endgroup$
    – AGibbons
    Oct 27, 2014 at 10:28
  • $\begingroup$ @AGibbons yes, booleans are known to have problems with pieces of geometry (verts, edges, faces) from the two objects occupying the exact same location. $\endgroup$
    – PGmath
    Oct 28, 2014 at 16:25
  • $\begingroup$ Is there a way to achieve the opposite effect? I mean, to show the object only while it is inside the cube, @gandalf3 ? $\endgroup$
    – invicente
    Jan 15, 2016 at 11:14

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