Softimage Xsi: Clouds/Procedural animation question

**I also posted this on the XSIbase forum, so I apologize if you're reading this twice.


I am trying to create an effect in which smoky or wispy clouds "morph" into the shape of various geometry. I'm trying to go about it using masks which animate to reveal one object after another.


My idea was to use a black (or transparent) and white gradient and then use a cloud or other procedural to animate the position of a color--and thus create a mask which will then be composited later in post.


I'm just trying some initial tests by simply surfacing a grid and trying to get the smoky cloud to rise from the bottom to the top--while at the same time animating accordingly.


Below is a link to a very simplified version of what I'm trying for. Unfortunately I'm not at my work computer and don't have XSI, so this simple Photoshopped example will have to do. Think of the the grey, blended-area as the smoky area. The image on the left is the initial gradient position and the image on the right is a later position. The problem is--using my method I have been unable to get the cloud prodecurual to control the blending position of my gradient node.





Does my method seem appropriate? If there is a better way to achieve this effect, I would love some advice. I'm still new to XSI.


Thanks.

-adam