Issue #7061: Added a 'Turtle star' sidebar

This commit is contained in:
Alexander Belopolsky 2010-11-09 18:40:03 +00:00
parent 922e904cca
commit 14fb79977b
5 changed files with 467 additions and 0 deletions

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@ -0,0 +1,10 @@
from turtle import *
color('red', 'yellow')
begin_fill()
while True:
forward(200)
left(170)
if abs(pos()) < 1:
break
end_fill()
done()

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%!PS-Adobe-3.0 EPSF-3.0
%%Creator: Tk Canvas Widget
%%For: Alexander Belopolsky
%%Title: Window .4315905424
%%CreationDate: Tue Nov 9 12:54:06 2010
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/space/space/space/space/space/space/space/space
/space/space/space/space/space/space/space/space
/space/space/space/space/space/space/space/space
/space/exclam/quotedbl/numbersign/dollar/percent/ampersand/quotesingle
/parenleft/parenright/asterisk/plus/comma/hyphen/period/slash
/zero/one/two/three/four/five/six/seven
/eight/nine/colon/semicolon/less/equal/greater/question
/at/A/B/C/D/E/F/G
/H/I/J/K/L/M/N/O
/P/Q/R/S/T/U/V/W
/X/Y/Z/bracketleft/backslash/bracketright/asciicircum/underscore
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] def
50 dict begin
% This is a standard prolog for Postscript generated by Tk's canvas
% widget.
% RCS: @(#) $Id$
% The definitions below just define all of the variables used in
% any of the procedures here. This is needed for obscure reasons
% explained on p. 716 of the Postscript manual (Section H.2.7,
% "Initializing Variables," in the section on Encapsulated Postscript).
/baseline 0 def
/stipimage 0 def
/height 0 def
/justify 0 def
/lineLength 0 def
/spacing 0 def
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/strings 0 def
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forall
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currentfont /Encoding get exch 1 exch put (\001) stringwidth
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ifelse
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forall
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% font ISOEncode font
% This procedure changes the encoding of a font from the default
% Postscript encoding to current system encoding. It's typically invoked just
% before invoking "setfont". The body of this procedure comes from
% Section 5.6.1 of the Postscript book.
/ISOEncode {
dup length dict begin
{1 index /FID ne {def} {pop pop} ifelse} forall
/Encoding CurrentEncoding def
currentdict
end
% I'm not sure why it's necessary to use "definefont" on this new
% font, but it seems to be important; just use the name "Temporary"
% for the font.
/Temporary exch definefont
} bind def
% StrokeClip
%
% This procedure converts the current path into a clip area under
% the assumption of stroking. It's a bit tricky because some Postscript
% interpreters get errors during strokepath for dashed lines. If
% this happens then turn off dashes and try again.
/StrokeClip {
{strokepath} stopped {
(This Postscript printer gets limitcheck overflows when) =
(stippling dashed lines; lines will be printed solid instead.) =
[] 0 setdash strokepath} if
clip
} bind def
% desiredSize EvenPixels closestSize
%
% The procedure below is used for stippling. Given the optimal size
% of a dot in a stipple pattern in the current user coordinate system,
% compute the closest size that is an exact multiple of the device's
% pixel size. This allows stipple patterns to be displayed without
% aliasing effects.
/EvenPixels {
% Compute exact number of device pixels per stipple dot.
dup 0 matrix currentmatrix dtransform
dup mul exch dup mul add sqrt
% Round to an integer, make sure the number is at least 1, and compute
% user coord distance corresponding to this.
dup round dup 1 lt {pop 1} if
exch div mul
} bind def
% width height string StippleFill --
%
% Given a path already set up and a clipping region generated from
% it, this procedure will fill the clipping region with a stipple
% pattern. "String" contains a proper image description of the
% stipple pattern and "width" and "height" give its dimensions. Each
% stipple dot is assumed to be about one unit across in the current
% user coordinate system. This procedure trashes the graphics state.
/StippleFill {
% The following code is needed to work around a NeWSprint bug.
/tmpstip 1 index def
% Change the scaling so that one user unit in user coordinates
% corresponds to the size of one stipple dot.
1 EvenPixels dup scale
% Compute the bounding box occupied by the path (which is now
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pathbbox
4 2 roll
5 index div dup 0 lt {1 sub} if cvi 5 index mul 4 1 roll
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6 index exch {
2 index 5 index 3 index {
% Stack now: width height string y1 y2 x y
gsave
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% -- AdjustColor --
% Given a color value already set for output by the caller, adjusts
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CL 2 lt {
currentgray
CL 0 eq {
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% x y strings spacing xoffset yoffset justify stipple DrawText --
% This procedure does all of the real work of drawing text. The
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% following arguments must be on the stack:
%
% x, y - Coordinates at which to draw text.
% strings - An array of strings, one for each line of the text item,
% in order from top to bottom.
% spacing - Spacing between lines.
% xoffset - Horizontal offset for text bbox relative to x and y: 0 for
% nw/w/sw anchor, -0.5 for n/center/s, and -1.0 for ne/e/se.
% yoffset - Vertical offset for text bbox relative to x and y: 0 for
% nw/n/ne anchor, +0.5 for w/center/e, and +1.0 for sw/s/se.
% justify - 0 for left justification, 0.5 for center, 1 for right justify.
% stipple - Boolean value indicating whether or not text is to be
% drawn in stippled fashion. If text is stippled,
% procedure StippleText must have been defined to call
% StippleFill in the right way.
%
% Also, when this procedure is invoked, the color and font must already
% have been set for the text.
/DrawText {
/stipple exch def
/justify exch def
/yoffset exch def
/xoffset exch def
/spacing exch def
/strings exch def
% First scan through all of the text to find the widest line.
/lineLength 0 def
strings {
cstringwidth pop
dup lineLength gt {/lineLength exch def} {pop} ifelse
newpath
} forall
% Compute the baseline offset and the actual font height.
0 0 moveto (TXygqPZ) false charpath
pathbbox dup /baseline exch def
exch pop exch sub /height exch def pop
newpath
% Translate coordinates first so that the origin is at the upper-left
% corner of the text's bounding box. Remember that x and y for
% positioning are still on the stack.
translate
lineLength xoffset mul
strings length 1 sub spacing mul height add yoffset mul translate
% Now use the baseline and justification information to translate so
% that the origin is at the baseline and positioning point for the
% first line of text.
justify lineLength mul baseline neg translate
% Iterate over each of the lines to output it. For each line,
% compute its width again so it can be properly justified, then
% display it.
strings {
dup cstringwidth pop
justify neg mul 0 moveto
stipple {
% The text is stippled, so turn it into a path and print
% by calling StippledText, which in turn calls StippleFill.
% Unfortunately, many Postscript interpreters will get
% overflow errors if we try to do the whole string at
% once, so do it a character at a time.
gsave
/char (X) def
{
dup type /stringtype eq {
% This segment is a string.
{
char 0 3 -1 roll put
currentpoint
gsave
char true charpath clip StippleText
grestore
char stringwidth translate
moveto
} forall
} {
% This segment is glyph name
% Temporary override
currentfont /Encoding get exch 1 exch put
currentpoint
gsave (\001) true charpath clip StippleText
grestore
(\001) stringwidth translate
moveto
} ifelse
} forall
grestore
} {cstringshow} ifelse
0 spacing neg translate
} forall
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@ -23,6 +23,16 @@ command ``turtle.forward(15)``, and it moves (on-screen!) 15 pixels in the
direction it is facing, drawing a line as it moves. Give it the command
``turtle.left(25)``, and it rotates in-place 25 degrees clockwise.
.. sidebar:: Turtle star
Turtle can draw intricate shapes using programs that repeat simple
moves.
.. image:: turtle-star.*
:align: center
.. literalinclude:: ../includes/turtle-star.py
By combining together these and similar commands, intricate shapes and pictures
can easily be drawn.