animation of cross section

I have a set of technical objects, some of them rotation symmetric, some cube shape. Now I want to show them as cross section, but the act of cross “secting” I want to animate as in the following picture:

I want it to open like a cake along the yellow line. How could I go about to do that? The cylindrical object have 18 segements. Do I have to delete them one by one or can I somehow “push” them together?
And how about the cube? It has a hole and the edges come together in the corners. I guess I will have to change that, like radial from the center to the outside?
I would very much appreciate if someone could put me on the right track.

You could cut it down the middle and mirror it relative to the 3D Cursor (which is snapped to the cut). When you annimate one half along X the other half should mirror the movement exactly.


Not sure if this would work, since I haven’t tried it, actually, but how about using a blend texture with a sharp cut-off and using an empty as the map input object?
OK, I just tried it on a simple cube and it seems to work ok. What I did was to turn down the alpha value of the cube to zero, turned the SpecTra value to zero, turned on Ztransp and assigned a blend texture to the cube. In the texture input channel, I activated the object option and typed in the name of the object which would control the location and size of the texture, in this case, Empty, since I created an empty object on the same spot as my cube. Map to to alpha. In the texture panel, I used a blend texture, added a colorband and tweaked the settings so that you have a black/white colorband with a sharp transition.
Then you just animate the empty and the object’s cross section is revealed.
You’ll just see the empty moving if you press Alt A in the 3d window.
Press anim to render the 30 frame animation and Play to play it.
Blender’s new transparency draw for the 3d window view doesn’t seem to be able to handle the alpha texture transparency. The entire cube goes invisible if I activate this from the Draw/Draw Extra panel… :-?
Not sure how to do an angular thing like you want, though.
Blend file uploaded to h4x’s site

Thank you Fligh!
That is a good idea for the rotation symmetrical objects. I will try it out. For the cube I might have to use a different approach since one could see the rotation which would look kind of strange.

Thank you grafix!
I downloaded your file and it gives me quite a bit to ponder about! I might combine this technique for the cube with that of Flight´s for the round parts.
Thank you very much for sharing!

hello grafix,
using a transparent texture like in your example “cuts open” the cube so it is “hollow”. I wonder if I could use another empty object and put it just a tick before the existing and give it a solid texture so everything up to this object would show transparent and the rest solid…this topic is very new to me and I will have to study your settings…

That’s done with manual mirror (not the modifier) and each half is animated seperately.


thank you fligh for the blend file, but I was thinking of the z-axis as rotation axis like here:
while modelling this example I got the idea that I could also use a transparent texture and rotate it instead of moving it only like in grafix example. I have to find out if that is possible.