[Caml-list] OCamlplot puzzle

[Matt Gushee <mgushee@havenrock.com>]

Hello, all--

I am trying to learn the OCamlplot API, and as a first step I have
written a simple program that is supposed to generate a PNG image with a
single colored rectangle (see code below). Well, the output is indeed a
PNG image, but there is no colored rectangle; the image is just solid
white. And apparently the image's colorspace is a 1-bit grayscale:

  bash-2.05a$ file /var/tmp/test.png 
  /var/tmp/test.png: PNG image data, 570 x 570, 1-bit grayscale,\
      non-interlaced

(? 1-bit grayscale? Didn't know there was such a thing. Doesn't 1-bit
mean monochrome by definition?)

I have been looking through the libplot documentation, and I can't find
anything about colorspace. I suppose I must be missing some simple step
in my program.

Any ideas what the problem is? 

  [ I'm running OCaml 3.06 on Debian GNU/Linux 3.0, with
    ocamlplot 0.4 and libplot 2.4.1 ]

Here's the code:

------ tryplot.ml ---------------------------------------------------

let out = open_out "/var/tmp/test.png" in
let pl = Plot.makepl Plot.PNG out [] in
Plot.openpl pl;
Plot.pencolor pl (Plot.Colorname "blue");
Plot.fillcolor pl (Plot.Colorname "red");
Plot.linewidth pl 2.;
Plot.filltype pl 1;
(*
let pt0 = { Plot.x = 20. ; Plot.y = 20. }
and pt1 = { Plot.x = 300. ; Plot.y = 200. } in
Plot.box pl ~p0:pt0 ~p1:pt1;
*)
Plot.fbox pl 20. 20. 300. 200.;
Plot.closepl pl;
Plot.deletepl pl;
close_out out

---------------------------------------------------------------------
  
-- 
Matt Gushee                 When a nation follows the Way,
Englewood, Colorado, USA    Horses bear manure through
mgushee@havenrock.com           its fields;
http://www.havenrock.com/   When a nation ignores the Way,
                            Horses bear soldiers through
                                its streets.
                                
                            --Lao Tzu (Peter Merel, trans.)
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