% turtle.ps -- graphics turtle.
% @author Eric Laroche
% @version @(#)$Id: pst-turtle.pro 1092 2019-10-01 20:19:35Z herbert $
%
% turtle.ps -- graphics turtle.
% Copyright (C) 1997-2001 Eric Laroche.
%
% This program is free software;
% you can redistribute it and/or modify it.
%
% This program 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.
%
% the '(graphics) turtle' is a 'cursor' that has a position (x and y
% coordinate), a heading and a pen up/down state. procedures as
% forward, left, etc. are used as drawing idioms.
%
% the turtle object consists of: cx cy phi penstate. cx and cy are the
% initialial coordinates, established when creating the turtle, they are
% the turtles zero coordinates. phi is the turtle heading, zero means
% in x direction (i.e. to the right), 90 means in the y direction (i.e.
% up). penstate is a boolean indicating whether the pen is down (true)
% or up (false).
% implicit to the turtle object is: currentpoint.
%
% note that using path constructing operators moveto, rmoveto, lineto,
% rlineto, arc, etc. will affect the turtle's state in a way that the
% turtle's current point is changed together with the postscript vm's
% current point by these operators. contrary the turtle's heading
% isn't affected by these operators.
%
% the turtle procedures indicate syntaxes using <turtle> (an array
% containing the turtle state) as abstract turtle object.
%
% no syntax is indicated with the abbreviated function names.
%
% these procedures are not handling newpath, closepath,
% setlinewidth, setlinejoin, setlinecap, stroke, fill, etc.
%
% a current point must be set before using the turtle object and after
% starting a new path. i.e. a typical initialization sequence would be
% e.g. 'newpath 200 200 moveto turtle 90 setheading'.
%
% create a turtle object.
% this saves the current point as zero point to return to by 'home'.
% a turtle object is an array of: [cx cy phi penstate].
% - turtle -> <turtle>
%
% on stack: { x y } boolean N@name type InitXnode
/saveNode {
tx@Dict begin
(Turtle) nodeCounter 2 string cvs concatstrings 32 rightTrim cvn { currentpoint } def
end
} def
%
/turtle {
% get initial position.
% initial position is current point.
2 setlinejoin
currentpoint
% phi and penstate
0 true
% note: not doing any newpath.
4 array astore
} bind def
% destroy a turtle object.
% note: this procedure serves for compatibility
% to older turtle formats.
% <turtle> unturtle -> -
/unturtle {
% return to turtle object's initial position.
dup 0 get
1 index 1 get % <turtle> cx cy
moveto
% note: not doing any newpath.
pop % -
} bind def
% return turtle object size.
% note: this procedure serves for compatibility
% to older turtle formats.
% - turtlesize -> 1
/turtlesize {
% 1 entry on the stack (an array with cx cy phi penstate).
1
} bind def
% normalize direction. phi must be >= 0 and < 360.
% <turtle> normalizephi -> <turtle>
/normalizephi {
dup 2 get % <turtle> phi
% note: denormalized typically by less than two circles,
% so the loops won't take too long.
% cut while larger or equal 2 pi.
{
dup 360 % <turtle> phi phi 360
lt {
exit
} if
360 sub
} loop
% increment while less zero.
{
dup 0 % <turtle> phi phi 0
ge {
exit
} if
360 add
} loop
exch dup 2
4 -1 roll
put % <turtle>
} bind def
% relatively move to, action depending on penstate.
% <turtle> dx dy pmoveto -> <turtle>
/pmoveto {
% move or draw, depending on penstate
2 index 3 get {
rlineto
} {
rmoveto
} ifelse
} def
% where we are, from initial point (in setxy coordinates).
% <turtle> xy -> <turtle> x y
/xy {
currentpoint % <turtle> x' y'
exch 2 index 0 get sub % <turtle> y' x
exch 2 index 1 get sub % <turtle> x y
} bind def
% calculate relative movements from setxy coordinates.
% <turtle> x y rxy -> <turtle> x' y'
/rxy {
3 -1 roll % x y <turtle>
xy % x y <turtle> x'' y''
5 -2 roll % <turtle> x'' y'' x y
exch 4 -1 roll sub
exch 3 -1 roll sub % <turtle> x' y'
} bind def
% logo language turtle functions
% put penstate in 'up' position.
% logo language turtle function
% <turtle> penup -> <turtle>
/penup {
% false means 'up'.
dup 3 false put
} bind def
% put penstate in 'down' position.
% logo language turtle function
% <turtle> pendown -> <turtle>
/pendown {
% true means 'down'.
dup 3 true put
} bind def
% advance in current direction.
% logo language turtle function
% <turtle> d forward -> <turtle>
/forward {
% dx is d cos phi.
1 index 2 get cos 1 index mul % <turtle> d dx
% dy is d sin phi.
2 index 2 get sin 3 -1 roll mul % <turtle> dx dy
pmoveto
saveNode
} def
% back up in current direction.
% logo language turtle function
% <turtle> d back -> <turtle>
/back {
neg
forward
} bind def
% change direction to the left (counterclockwise, positive direction).
% logo language turtle function
% <turtle> omega left -> <turtle>
/left {
1 index 2 get % <turtle> omega phi
add % <turtle> phi'
1 index 2 3 -1 roll put
normalizephi
} bind def
% change direction to the right (clockwise, negative direction).
% logo language turtle function
% <turtle> omega right -> <turtle>
/right {
neg
left
} bind def
% move to a specified point.
% logo language turtle function
% <turtle> x y setxy -> <turtle>
/setxy {
rxy % <turtle> x' y'
pmoveto % <turtle>
} bind def
% move to a specified point (only x changes).
% logo language turtle function
% <turtle> x setx -> <turtle>
/setx {
0 rxy % <turtle> x' y'
pop 0 pmoveto % <turtle>
} bind def
% move to a specified point (only y changes).
% logo language turtle function
% <turtle> y sety -> <turtle>
/sety {
0 exch rxy % <turtle> x' y'
exch pop 0 exch pmoveto % <turtle>
} bind def
% set the heading.
% logo language turtle function
% <turtle> phi' setheading -> <turtle>
/setheading { 1 index 2 3 -1 roll put normalizephi } bind def
% set heading towards a point.
% logo language turtle function
% <turtle> x y towards -> <turtle>
/towards {
rxy % <turtle> x' y'
% check if both zero.
1 index 0 eq 1 index 0 eq and {
% set heading to zero.
pop pop 0
} {
exch atan
} ifelse
setheading
} bind def
% go home; heading to zero.
% logo language turtle function
% <turtle> home -> <turtle>
/home { 0 dup setxy 0 setheading } bind def
% get x coordinate.
% logo language turtle function
% <turtle> xcor -> cx <turtle> x
/xcor { xy pop } bind def
% get y coordinate.
% logo language turtle function
% <turtle> ycor -> <turtle> y
/ycor { xy exch pop } bind def
% get heading.
% logo language turtle function
% <turtle> heading -> <turtle> phi
/heading { dup 2 get } bind def
% get pen state.
% logo language turtle function
% note: only the turtle relevant stuff given.
% <turtle> drawstate -> <turtle> penstate
/drawstate { dup 3 get } bind def
%
% logo language turtle function abbreviations
%
/bk { back } bind def
/fd { forward } bind def
/lt { left } bind def
/pd { pendown } bind def
/pu { penup } bind def
/rt { right } bind def
/seth { setheading } bind def
%
end
% end of pst-turtle.pro
