A tale of 2 holes in the clouds.

[Upon Infinity]

I might need forum help on this one.

Trying to punch a hole in the clouds.  I even have an example file of how to do it successfully.  For some reason, it's not transferring over, despite copy and pasting the exact nodes to do it.

Example 1 (Incorrect) Nodes are functioning, but instead of hole in the clouds, produces total cloud over mask.

Example 2 (Correct): Nodes produce hole through clouds successfully.  

Colour adjust and image map shaders are exactly the same and were ported over from example 2. They even use the same mask file.

What might produce the inverted result?

[WAS]

Have you tried making sure "Invert mask" is checked in the cloud fractals?

[Upon Infinity]

Yes, as indicated in the screenshots.  It's either something that's further up or down from the 2 nodes (colour adjust/image map).

[Dune]

A mask may (maybe) not work exactly as you expect as colors in the density shader are unclamped. I don't actually know what a mask does to negatives. So I would feed mask into final density, maybe also you need to change color from linair to convert to lineair, or the other way round.

[cyphyr]

Try using a compliment colour function node and make sure your simple shape is actually large enough.

[Matt]

Are you using "coverage adjust" (in the cloud layer, not the fractal)? If this has a positive value it will produce cloud where the hole is. The masked density fractal might be 0, but the cloud layer's coverage adjust setting adds to this density.

[Upon Infinity]

Are you using "coverage adjust" (in the cloud layer, not the fractal)? If this has a positive value it will produce cloud where the hole is. The masked density fractal might be 0, but the cloud layer's coverage adjust setting adds to this density.

That was it.  Thanks, Matt.

[Upon Infinity]

Try using a compliment colour function node and make sure your simple shape is actually large enough.

I take it, then, that this is an alternate method to my camera projection?  Is this easy to position where you want it?  I use camera projection as it's quite easy to light a specific area.  I wasn't aware of the coverage adjust limitations.

[Upon Infinity]

A mask may (maybe) not work exactly as you expect as colors in the density shader are unclamped. I don't actually know what a mask does to negatives. So I would feed mask into final density, maybe also you need to change color from linair to convert to lineair, or the other way round.

Sounds interesting.  Which node would be final density?

[Dune]

One of cloud inputs, fourth/fifth I believe.

[cyphyr]

Unfortunately there is no good guaranteed way of getting holes inn clouds exactly where you want them. Both the image map (either Y projected or camera projected) and the simple shape shader suffer from having vertical sides cutting un-realistically through the clouds.

A not ideal but possibly artistically best meathod would be to create a cloud layer with a high coverage so there are some small holes here and there. You can then use a transform node to move the cloud fractal somewhere where the hole is in the right place and the light is illuminating the location you want.

[Dune]

I have posted a method several times that works perfectly, but I'll describe again: using a small black image map with soft white circle, projected by camera onto clouds (masking it), by copying sun elevation and angle. Invert color before masking, and set camera angle as narrow as you like sunspot. Location of camera where you want the sun spot. Or add a few of them.

[Upon Infinity]

I have posted a method several times that works perfectly, but I'll describe again: using a small black image map with soft white circle, projected by camera onto clouds (masking it), by copying sun elevation and angle. Invert color before masking, and set camera angle as narrow as you like sunspot. Location of camera where you want the sun spot. Or add a few of them.

I was using just such a mask, but it still produces hard edges.

[cyphyr]

I think it can work very well (Dunes method) but as with all things Terragen it is down to a combination of circumstances.
The angle of the sun and camera, the thickness of the cloud and the exact nature of the Cloud fractal that is being cut through.

[Dune]

Should depend on how hard your white circle is, and you may have to switch between lineair and convert to lineair.