3 clouds questions plus one

Started by romi, January 30, 2008, 01:18:16 pm

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1. is there a way to define where clouds go in the screen? for example, i want clouds to only show up in the upper half of the screen. is that possible? currently i'm using crop and then some clean up afterwards. but i'm wondering if there's another method.

2. the lower clouds are casting shadows & light beams unto the surface. is there a way to disable this and still keep the shading & shadows on the clouds themselves?

3. is there a way to define or import a shape (a curve from illustrator maybe) and use it to define the shape of a cloud? i would like a little bit more control of designing and arranging the clouds in my scene. currently i render a few and then i cut and paste in photoshop for the optimal design and arrangement.

4. ok, not a cloud question but what is acceleration cache? i'm getting hints here & there in the forum but maybe someone can give me the explanation on this feature.

thanks in advance for the help!



1. You can random seed until you get what you want and/or try to blend the clouds with a powerfractal or distance shader.

2. You could try to lower the haze glow amount.

3. You can import an image via the image map shader and use it as a cloud mask or as blend shader

4. I don't really know. It makes renders go faster or slower depending on what settings you have set up.  ;D And it can cause problems sometimes.


A4 - If you are used to Maya and its fluid effects, this is really easy to understand. Cache is basically a small file created by the program to store information. What kind of information depends on the application or what is the data being used for. In this case the cache file created would be used for clouds. Now I am not sure what kind of data TG2 stores in this file but I am guessing it is mostly cloud GI info and also some general cloud shape/size/warping info which would help renderer speed up the rendering process. No acceleration cache means this file is not created and everything is being calculated while rendering. Hence longer render time but more accurate results.
"His blood-terragen level is 99.99%...he is definitely drunk on Terragen!"


Acceleration cache is probably a setting for how memory handles the data for the cloud and its settings.
So this is Disney World.  Can we live here?


Take a look at this Wikipedia Entry on the subject which might be of help on what a cache is and what it is for.

Regards to you.



1: You can define where clouds show up in various ways. For your specific purposes I would use a through-camera-projected Image Map Shader as a Blend Shader input of your Cloud Density Shader input. Render the scene once at low detail, then open the resulting image in an image editor and create a gradient or hand-drawn mask that has white where you want clouds to show up and black where you don't want them to show up. Use intermediate shades of gray to smooth the transition. Save as BMP then load this image in your Image Map Shader.

2: I don't think you can turn off the shadows just on the terrain at this point. The best you could do is turn off "enable secondary" in the cloud shader, render just the terrain with a crop render, then composite with a normal render of the top (with enable secondary turned on).

3: You can't control clouds to this degree yet, although you can use image masks, either through-camera or Plan Y projected. Through Camera will allow you to directly define the cloud shapes *as they will be seen by the camera*, although getting realistic edges and shapes can be difficult. Plan Y lets you define the cloud shapes using a mask projected from above. Use the above described technique to mask cloud shapes in this way.

4: The acceleration cache is a rendering optimization that speeds up cloud rendering, but can sometimes cause visual artifacts. That's why there are multiple settings available. If you get strange lines in your clouds in a scene, try turning down the acceleration cache.

- Oshyan


thank you guys so much for the tips & explanations! it is much appreciated.