What do you call this effect ?

[Ofnuts]

Actually very linear... The tops of the black strips are evenly spaced 40px part and the width of the white strips grows by 3 pixels.

Of course the true question is: is there a way to produce this by a clever use of one of the marvelous Ofnutsian scripts? And of course the answer is yes:

• Create a path that delimits a wide strip at one end
  
• Create a path that delimits a narrow strip at the other end
  
• Use path-inbetweener to generate the intermediate strips
  
• Merge the visible paths, path-to-selection, bucket-fill