When pressure is applied, it alters the state of the modules and causes them to reflect light - appearing as white lines on the reflective, pressure - sensitive, plastic LCD surface. (newatlas.com)
I was particularly interested in one small early painting of narrow vertical black and white lines of uneven length. (ayearofpositivethinking.com)
It's an app called Just a Line that lets you draw white lines in the air. (theverge.com)