
What it has to do with your original question is this: many times 
beginning X users (heck, experienced X users too!) write small test
programs.  Many times they forget to draw only in response to expose
events, and thus see unpreditable results whereby sometimes the application's
graphics show up, and sometimes they don't.  We're just trying to
eliminate all the "easy" explanations  for why you're not seeing your
graphics. 

That being said, why don't you try copying different planes to your
window other than 16 (== 1 << 4).  Try 1, 1<<1, 1<<2, ..., 1<<7
to see it you get any output.  Since you're dipslaying only a single 
plane of your data, it's possible that all the pixel values in your
pixmap have the same value for that color plane.

	Ken
