viewer vs viewport

viewer

noun
  • Someone who views a spectacle; an onlooker or spectator. 

  • The manager of a colliery, who directs its workings and ventilation. 

  • Someone who watches television. 

  • Any optical device used to view photographic slides. 

  • A program that displays the contents of a file. 

viewport

noun
  • A viewing window. 

  • A typically rectangular region representing the range or area currently visible (within a window, screen, etc.). 

verb
  • To clip (an image or region) so that it fits in a viewport. 

How often have the words viewer and viewport occurred in a corpus of books? (source: Google Ngram Viewer )