%!
%
% Date: Thu, 26 May 88 01:09:37 EDT
% To: NeWS-makers@brillig.umd.edu
% Subject: bez program
% From: toms@ncifcrf.gov
%
% Display this file using psview. ("psview bez.ps")
%
% bez version 2.02  1988 May 26 TDS
%
% AUTHOR:
% Tom Schneider
% Frederick, Maryland
% toms@ncifcrf.gov
%
% LANGUAGE: PostScript
%
% DESCRIPTION:
% Bez creates a set of colorful Bezier curves using the
% curveto function in PostScript.  Each of the 4 coordinates
% that define each Bezier curve has its own velocity that is
% initialized with random numbers.  The 4 coordinates bounce
% around within the field of view, and their velocities
% are altered slightly at random.  The color of each
% curve is also altered slightly from the previous curve.
%
% USE:
% Under NeWS 1.1 run with the command
%    psview bez
% Everytime you iconize and re-open the window, you will get
% a different pattern, since the random numbers change...
% Note: you can change the size of the window to be sure to get
% the black box which outlines the bounds of the coordinates.
% (The curve goes slightly outside the box sometimes.)
%
% BUGS:
% A proper window rather than psview would be nice, in which one
% could toggle the various constants and redraw with a single touch.
%
% Bez runs beautifully on my Sun 3/260C, but it doesn't
% work on a Sun 3/50.  The first curve appears in black and then it
% is overwritten with white, so almost nothing shows up.  The problem
% is not corrected by using 2 setlinequality, by keeping the hue fixed
% or by setting the width to 2.  So much for portability.
% If you figure it out, let me know please.
%
% It would make a nice lockscreen, if lockscreen existed under NeWS...
%
% The placement of the image doesn't work quite right in psview.
%
% CONSTANTS for you to play with:
/acc 0.5             def % acceleration of velocity changes (0.5 is nice)
                         % try 0 with numbercurves at 1000!
/huestep 0.01        def % rate of hue change (0.01 is nice)
/maxbound 750        def % maximum x and y axis (750 is nice)
/numbercurves 500    def % number of curves to put down (500 is nice)
/speed 2             def % velocity increments (2 is nice)
/width 1             def % line width, wider is slower, but prettier (1 is nice)

% other constants
/hue random          def % initialize hue

% set up line sizes
1 setlinequality
width setlinewidth

/scran { % chose a random number scaled between 0 and maxbound
  random maxbound mul
} def

% define positions
  /xp0 scran def
  /yp0 scran def

  /xp1 scran def
  /yp1 scran def

  /xp2 scran def
  /yp2 scran def

  /xp3 scran def
  /yp3 scran def

/veran { % chose a random velocity between -speed and speed
  random 2 mul 1 sub speed mul
} def

% define velocities
  /xv0 veran def
  /yv0 veran def

  /xv1 veran def
  /yv1 veran def

  /xv2 veran def
  /yv2 veran def

  /xv3 veran def
  /yv3 veran def

/go { % construct a single Bezier curve
  % draw the current curve defined by the 4 points
  newpath
    xp0 yp0 moveto
    xp1 yp1
    xp2 yp2
    xp3 yp3
    curveto
  stroke

  % update positions
  /xp0 xp0 xv0 add def
  /xp1 xp1 xv1 add def
  /xp2 xp2 xv2 add def
  /yp3 yp3 yv3 add def

  /yp0 yp0 yv0 add def
  /yp1 yp1 yv1 add def
  /yp2 yp2 yv2 add def
  /xp3 xp3 xv3 add def

  % make velocities drift randomly!
  /xv0 xv0 veran acc mul add def
  /xv1 xv1 veran acc mul add def
  /xv2 xv2 veran acc mul add def
  /xv3 xv3 veran acc mul add def

  /yv0 yv0 veran acc mul add def
  /yv1 yv1 veran acc mul add def
  /yv2 yv2 veran acc mul add def
  /yv3 yv3 veran acc mul add def

  % reverse velocities at boundries
  xp0 maxbound gt {/xv0 0 xv0 sub def} if
  xp1 maxbound gt {/xv1 0 xv1 sub def} if
  xp2 maxbound gt {/xv2 0 xv2 sub def} if
  xp3 maxbound gt {/xv3 0 xv3 sub def} if

  yp0 maxbound gt {/yv0 0 yv0 sub def} if
  yp1 maxbound gt {/yv1 0 yv1 sub def} if
  yp2 maxbound gt {/yv2 0 yv2 sub def} if
  yp3 maxbound gt {/yv3 0 yv3 sub def} if

  xp0 0 lt {/xv0 0 xv0 sub def} if
  xp1 0 lt {/xv1 0 xv1 sub def} if
  xp2 0 lt {/xv2 0 xv2 sub def} if
  xp3 0 lt {/xv3 0 xv3 sub def} if

  yp0 0 lt {/yv0 0 yv0 sub def} if
  yp1 0 lt {/yv1 0 yv1 sub def} if
  yp2 0 lt {/yv2 0 yv2 sub def} if
  yp3 0 lt {/yv3 0 yv3 sub def} if

  % change the color
  /hue hue huestep add def % modify the hue
  hue % this is the hue
  1.0 % this is the saturation
  1.0 % this is the brightness
  sethsbcolor % reset the color
} def

% main calls

erasepage

% draw a curve around the field so that psview
% can figure out where to place the graph
newpath
          0        0 moveto
   maxbound        0 lineto
   maxbound maxbound lineto
          0 maxbound lineto
   closepath
stroke

% produce the curves
  numbercurves{
    go
    pause
  } repeat