You Could also write a simple expression, kind of like this :
imagePlane_Top.transparancy = slider.translateX ;
imagePlane_Side.transparancy = slider.translateX ;
imagePlane_Front.transparancy = slider.translateX ;
explanation:
imagePlane_Top = name of the shader for the image plane.
imagePlane_Top.transparancy = The transparancy attribute on the shader.
slider.translateX ; = the name of the slider object.
slider.translateX ; = the translation attribute for the slider object.
This would result in change of transparancy if you move the slider object in the X direction. Completely transparant if you move the slider object more than 1 unit.
You could add some math to the expression if you would like to move the slider over a longer distance before it get completely transparant.
example :
imagePlane_Top.transparancy = slider.translateX / 10 ; and you would have to move the object 10 units before it would be completely transparent.
This is just an alternative way to do the same as with set driven key. Set driven key kind of writes the expression for you, but if you write your own expression you would have complete control over what actually happens, and would be able to do much more mathematically correct control, as this could be used for more ways of controlling stuff, and is easily editable in the expression editor if needed - where set driven key is harder to do edits on.
I hope you get the point.
Carsten Lind
Senior 3D Artist,
Maya Software Manager & Maya Instructor
LEGO Systems A/S