I want to do something like whiteboard animation in Blender (for example, like this video).
Suppose I have an image with simulated hand-drawing and a transparent background. I can prepare this image in Inkscape (or any other software) and import it to Blender by using addon “Import Images as Planes” or manually.
I can imagine how to make an animation of the moving hand with a pencil. It can be done by driver moving along a given curve. But I want the same driver (sphere for example) to control the visibility of areas of my image. Other words I want to show only those parts of the image where the specified object (driver) was already moving. Thus it will be possible to realize an animation of gradual and realistic appearance of my hand-drawing image.
What is the best and easiest way to implement such a thing?