title: Drawing over other applications in Android
body: <p>There is an interesting application called <a href="https://play.google.com/store/apps/details?id=com.urbandroid.lux" rel="noreferrer">Twilight</a> which appears to simply draw over all applications with a reddish filter to remove blue light during nighttime hours (presumably to help sleep). </p>
  
  <p>I'm interested in doing something similar, but not necessarily for sleep purposes. I'd like to draw text or a watermark over everything on the phone. How can I do this (draw an Activity or something like it over everything) in Android?</p>