There are a couple things you can do. First, you can try putting a Transform shader and using the Translate function on the Cloud Layer Density Fractal (just plut the Transform in-between the Density Fractal and the Cloud Layer). The use of this is if you find a formation you like you can move it around in the scene by adjusting the translate values and essentially put it where you want it. That's only useful of course if there are no other bits that show up when you move the bit you like into position. You might be able to help with this by making your Lead-in scale larger, for larger formations, or by using a Blend Shader on your Density Fractal to make large patches of empty space, then move an empty patch over your camera so clouds are only in the distance.
An alternative method would involve using a through-camera mask. You could either use a simple gradient to mask clouds higher in the view (and therefore closer) out and keep clouds on the horizon, or you could actually come up with a scene you like and if there are nearby clouds just *paint them out* in a mask. This last approach is pretty cool and is probably how I'd do it.
First create setup the scene with some clouds where you want them, even if there are clouds where you don't want them.
Now create a new camera to use for the masking process. You'll want it in basically the same position as your current camera, but it's nice to have it separate in case you want to move your real camera.
Next create an Image Map shader and hook it to the Blend Shader input of your Density Fractal. For Projection choose Through Camera then specify the camera you just added. We won't load an image just yet. Be sure to turn on Blend By Shader in the Density Fractal.
Now do a quickie render of the scene, low detail, but with the clouds in place. Save this and open it in an image editor. Make everything white *except the clouds you don't want*, which you should make black. Hopefully they're somewhat sperate from the background clouds so you don't have to worry about making the edge of your mask look realistic - trying to paint realistic cloud edges for a mask is tough.
Now save your new mask in one of the formats TG2 can load and load it into the Image Map Shader. Try another test render and see if the clouds are masked out. You may need to invert the blend shader if I've gotten the masking colors reversed. If it doesn't work either way then I may have made a mistake in my instructions.
But hopefully you get the idea and can experiment to make it work.
Basically you're projecting a mask image straight out through the camera into the scene and using it to mask your cloud density function. This is a pretty cool technique that can be used in many situations. One interesting possibility is using it to mask populations to keep them limited only to the view of the camera at any given time, thus keeping population times and memory use down.
There's lots of power in the various shaders and functions to be toyed with. I thought for example of using a Distance Shader for this, but I couldn't get it to work as I expected. I'm guessing it's an error on my part though.
- Oshyan