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UserCg21
11-23-2010, 02:44 PM
Hi there,

for a project I am working on I was wondering if it`s possible to cut a hole in the sky. In the scene there`s a big open landscape and a mountain in the middle of the camera view. I have two spectral cloud layers to create an overcast and stormy day. Now I want to have something like a hole in the sky above the mountain with light shining through it onto the mountain.
Is there any possibilty to achieve that?

cheers

xad
11-24-2010, 05:53 PM
You could use the 'dissolve near objects' setting in the cloud editor to achieve that:

Create an object (something like a cylinder should work) and scale / position it in the cloud layer where you want the hole to be. In the clouds tab of the atmosphere editor select the cloud layer, right click the cloud material and choose 'edit material' to open up the cloud material editor. In the 'lighting & effects' tab of the editor activate 'dissolve near objects' and adjust the settings. Select the object that you created for the hole and activate 'hide from render'.

edit: If it does not work you may have to move / scale your hole object around a bit.

UserCg21
11-24-2010, 10:23 PM
Hey xad,

That`s exactly what I did this morning. I found it accidentally in a tutorial about another topic and it works perfectly. But is it possible that this "trick" only works with spectral cloud layers? When I choose standard clouds there`s no option "dissolve near objects".

Anyway .... thanks for your response.

xad
11-26-2010, 06:03 PM
Standard clouds are more or less just a texture that's projected onto the sky. You'll notice that you can't even access most of the settings like 'height' or 'shadow density' for them. Also the cloud material editor for standard clouds is basically just a renamed material editor with some features disabled.

I haven't used standard clouds for a while but I believe they don't affect the lighting or cast shadows into your scene like spectral clouds do. So you should'nt need to cut a hole into them to get the sun shine trough.

If you have a standard cloud layer in you scene and want to cut a hole into it, you could adjust the 'transparency production' function in the cloud editor.

UserCg21
11-29-2010, 11:21 AM
That makes sense. Thank you for the explanation.
So it sounds like that you have quite a good knowledge of Vue. How would you go on with the effect I described?
The overall sky color is greyish/brownish to create a dusty and dirty industrial atmosphere. As I described there is the big mountain with the hole in the sky above it. Now we want the sky you can see through the hole to have a bluish color and the sunbeams shining onto the mountain. We tried to use the godrays but that increased rendertimes drastically and is not exactly what we wanted to achive. Is it possible to render the cloud layers and the sky as seperate channels and then do the sky color and sun beams in After Effects?

xad
11-30-2010, 12:08 PM
I think it could be difficult to get the scene setup with godrays in a way that it looks exactly as you want it.

One problem would be that you have no direct control over the godrays exept for switching them on/off. You have to change your atmosphere and cloud settings to change their apperance. You will most likely get a result with nice looking godrays but no visible blue sky behind it or the opposite. Also, atmospheres with godrays are often slow to render especially when you need to increase the quality settings to reduce noise.

It's sure a good idea to render some extra layers/channels for editing the render in post. This is easily done with Vue's g-buffer & multi-pass render options. A 'cloud mask' could be helpful for your project. I believe it's not possible to render out the godrays as a seperate layer but I'm not sure about that. You could also organize your scene in layers through the world browser and switch them on/off as needed.

In the end it depends a lot on what exactly you need, some effects are difficult to do in post while others are easily done.

If you can get the result you're looking for by adding the godrays in photoshop or after effects then i would definitely recommend to do it that way. You'll have much more control and it's a lot easier and faster to change something.

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