Making new items in an array fade in I'm working on an animation in Blender 2.8 wherein a line is increasing in length over the course of 40 frames. I'm using the array modifier, so a discrete rectangular shape is duplicated along the length of the line.

Using keypoints on the array count (from 1 to 25) works, but the new items simply pop into existence along the line. 

Is there a way to make these new items fade in, going from transparent to opaque? Perhaps using nodes? I'm going to be rendering in Cycles.
Please check the BUILD modifier (you can also apply it to lines).
BUILD modified let you animate the generation of a line and on the line/path you can control easily the radius/thickness.

Make 2 curves: one path (the line), one circle or square
one the line apply a GEOMETRY &gt; BEVEL &gt; OBJECT &gt; choose the circle or the square
Edit the size of the path with ALT+S (you can &quot;inflate&quot; a node of the path)
apply the BUILD modifier to the line.
animate and have fun