%%%% prbla_01.ldf
%%%% Created by Laurence D. Finston (LDF) Thu Nov 10 15:27:39 CET 2005

%% * (1) Copyright and License.

%%%% This file is part of GNU 3DLDF, a package for three-dimensional drawing. 
%%%% Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 The Free Software Foundation 

%%%% GNU 3DLDF is free software; you can redistribute it and/or modify 
%%%% it under the terms of the GNU General Public License as published by 
%%%% the Free Software Foundation; either version 3 of the License, or 
%%%% (at your option) any later version. 

%%%% GNU 3DLDF is distributed in the hope that it will be useful, 
%%%% but WITHOUT ANY WARRANTY; without even the implied warranty of 
%%%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
%%%% GNU General Public License for more details. 

%%%% You should have received a copy of the GNU General Public License 
%%%% along with GNU 3DLDF; if not, write to the Free Software 
%%%% Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

%%%% GNU 3DLDF is a GNU package.  
%%%% It is part of the GNU Project of the  
%%%% Free Software Foundation 
%%%% and is published under the GNU General Public License. 
%%%% See the website http://www.gnu.org 
%%%% for more information.   
%%%% GNU 3DLDF is available for downloading from 
%%%% http://www.gnu.org/software/3dldf/LDF.html. 

%%%% Please send bug reports to Laurence.Finston@gmx.de
%%%% The mailing list help-3dldf@gnu.org is available for people to 
%%%% ask other users for help.  
%%%% The mailing list info-3dldf@gnu.org is for the maintainer of 
%%%% GNU 3DLDF to send announcements to users. 
%%%% To subscribe to these mailing lists, send an 
%%%% email with ``subscribe <email-address>'' as the subject.  

%%%% The author can be contacted at: 

%%%% Laurence D. Finston 
%%%% c/o The Free Software Foundation, Inc.
%%%% 51 Franklin St, Fifth Floor 
%%%% Boston, MA  02110-1301 
%%%% USA 

%%%% Laurence.Finston@gmx.de 
 


%% Run these commands:

%% 3dldf prbla_01.ldf
%% mpost prbla_01
%% tex prbla_01.txt
%% dvips -o prbla_01.ps prbla_01.dvi 
%% gv prbla_01.ps &

verbatim_metapost "ahlength := .25cm;";

verbatim_metapost "verbatimtex \magnification=\magstep5 \font\large=cmr12 etex";
verbatim_metapost "verbatimtex \font\Large=cmr17 etex";

focus f;
set f with_position (0, 10, -20) with_direction (0, 10, 100) with_distance 15; 

picture axis_picture;
picture save_picture;

%% **** (4) axis_picture.

beginfig(0);
pickup blue;

pickup pencircle scaled (1mm, 1mm);

axis_x_lft   := 10;
axis_x_rt    := 10;
axis_y_bot   := 10;
axis_y_top   := 10;
axis_z_front := 10;
axis_z_back  := 10;

%drawarrow origin -- (-axis_x_lft, 0) with_color blue;
drawarrow origin -- (axis_x_rt, 0) with_color blue;
label.bot("x", (axis_x_rt, 0, -.1));

%drawarrow origin -- (0, -axis_y_bot) with_color blue;
drawarrow origin -- (0, axis_y_top) with_color blue;
label.lft("y", (0, axis_y_top)); 

%drawarrow origin -- (0, 0, -axis_z_front) with_color blue;
%drawarrow origin -- (0, 0, axis_z_back) with_color blue;
%label.lft("z", (0, 0, axis_z_back)); 

axis_picture := current_picture;
clear current_picture;
endfig; 


color_vector cv;
cv += red;
cv += green;
cv += blue;
cv += cyan;
cv += yellow;
cv += magenta;

beginfig(1);


parabola p;

path q[];

set p 
   with_parameter 3
%  with_vertex vertex  
%  with_focus p_focus  
   with_extent 7cm;

draw p; % with_color cv0;

p_last := size p - 1;

for j = 0 upto 6:
   q[j] += get_point (j * 3) p;
   q[10 + j] += get_point (p_last - (j * 3)) p;
endfor;

%dotlabel.top(0, p);


for i = 1 upto 23:
   rotate p by 7.5;

   for j = 0 upto 6:
      q[j] += get_point (j * 3) p;
      q[10 + j] += get_point (p_last - (j * 3)) p;
   endfor;

if is_even i:
   draw p ;% with_color cv[i];
fi;

endfor;

for j = 0 upto 6:
   q[20 + j] := q[j] .. q[10 + j];
   clear_connectors q[20 + j];
   q[20 + j] += ..;
   q[20 + j] += cycle;
   draw q[20 + j];
endfor;

%dotlabel.lft(0, p); 

save_picture := current_picture;


%output axis_picture with_focus f;
output current_picture with_focus f;
clear current_picture;

if false:
   verbatim_metapost "verbatimtex \setbox0=\hbox{parabola:\space} etex"; 
   verbatim_metapost "verbatimtex \setbox1=\hbox{focus:\space} etex"; 

   y_value     := -11;
   shift_value := -1;


   label.rt("{\large Perspective Projection}", (0, y_value));

   y_value -= .5;
   y_value += shift_value;

   label.rt("\copy0", (0, y_value));
   y_value += shift_value;
   label.rt("\hskip\wd0 vertex at origin", (0, y_value));
   y_value += shift_value;
   label.rt("\hskip\wd0 parameter $=$ 3cm", (0, y_value));
   y_value += shift_value;
   label.rt("\hskip\wd0 axis $=$ positive x-axis", (0, y_value));

   y_value -= .5;
   y_value += shift_value;

   label.rt("\copy1", (0, y_value));
   y_value += shift_value;
   label.rt("\hskip\wd1 position: (0, 10, -20)", (0, y_value));
   y_value += shift_value;
   label.rt("\hskip\wd1 direction: (0, 10, 100)", (0, y_value));
   y_value += shift_value;
   label.rt("\hskip\wd1 distance: 10", (0, y_value));
   y_value += shift_value;
fi;

endfig with_projection parallel_x_y;

beginfig(2); 
output save_picture with_projection parallel_x_y;
if false: 
   label.rt("{\large Parallel Projection, X-Y Plane}", (0, -8));
fi; 
endfig with_projection parallel_x_y;

beginfig(3); 
output save_picture with_projection parallel_x_z;
if false: 
   label.rt("{\large Parallel Projection, X-Z Plane}", (0, -8));
fi; 
endfig with_projection parallel_x_y;

beginfig(4); 
output save_picture with_projection parallel_z_y;
if false: 
   label("{\large Parallel Projection, Z-Y Plane}", (0, -8));
fi; 
endfig with_projection parallel_x_y;

verbatim_metapost "end";

end;