title: Opposite for OpacityMask
body: <p>It masks the source item with another item, so the source is visible only where the mask is opaque. How to make source visible only where the mask is transparent?</p>
  
  <p>Currently it's done with a shader, but I want to replace that.</p>
  
  <p>Can't invert the mask, because it consists of multiple images: the sum of individually inverted images is not the same as the inversion of the sum.</p>