This should be the perfect example,
Here the link https://www.raywenderlich.com/5246-u…render-targets
As you can see here this tutorial, link the AxisValue to the Brush Size, using of course some nodes for multiply, add, and clamp , and set the end value.
You can plug any variable inside the first X10, instead of the axis value, and … well… basically you can plug variable wherever you have the right kind of pin-Variable.
PS:Maybe the renderstuff is to complex, but you can use the mouse input, to move a cube, or anything else.
try something simple!