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for an animation I want to create a fluffy cloud scenery (with the internal render engine) To to this, I created severeal cloud shaped meshes- each of them got a particle system. Over that I build a bounding box mesh with a volume shader and a point density texture to drive the density of the volume. No problem so far. I get a pretty nice cloud with this setup but after adding a second one, I get bad results. They are intersecting.

I could render every cloud on a seperate render layer, but this would be a tidy task. After all I have 26 clouds.

enter image description here

enter image description here

What is the problem here? Which option is unchecked? I cant find it.

Thanks for your help

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  • $\begingroup$ Is it possible you could upload the .blend? $\endgroup$ – gandalf3 Aug 11 '15 at 2:22
  • $\begingroup$ Yes of course ~ I uploaded a stripped down blend dropbox.com/s/uco29g48e4odwwf/clouds_stack.7z?dl=0 $\endgroup$ – Rembrandt Aug 11 '15 at 12:06
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    $\begingroup$ Switching the transparency mode of the cubes to Raytraced helps a little, but prevents alpha-transparency and still doesn't render volumes inside them.. Not sure if this is even possible with BI? Maybe you could try combining the particle systems and using just one large cube.. $\endgroup$ – gandalf3 Aug 11 '15 at 21:44
  • $\begingroup$ I figured out, it isnt possible and this is really bad for me. I could use a giant domain box, but I have 4 different cloud shader - from fluffy to thick. So I need to render 4 passes and combines them later but there is a problem ~ the overlapping. I dont know how to handle it :/ Anyway. Thanks for your help. $\endgroup$ – Rembrandt Aug 12 '15 at 7:51
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I think you can solve this by using either one of 2 workarounds.

Scaling clouds domain by Z axis

This is kind of lazy solution, which assumes scaling domain cube of the fluffy clouds (those everywhere in the bottom). After domain is no longer intersecting with clouds in the foreground (left / right), there's no intersection.

enter image description here

Processing rendered OpenEXR images

  1. Start with moving fluffy clouds (those in the bottom) with their domain to separate layer (assuming light sources are on a layer turned on in any case). Set up output format as OpenEXR Multilayer.
  2. Render and save image. Do the same with big clouds on the left and right (so that they were moved together to the same layer).
  3. Having 2 .exr images, you can import them in another scene, delete RenderLayers node to render only from compositor and mix clouds with AlphaOver node (make sure Channels of the image to draw is set to Color and Alhpa).


Rendered clouds (with and without black layer added for transparency demonstration):

enter image description here
The result is the same for both solutions

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