Turtle Graphics
Revision as of 09:50, 8 June 2011 by Michael Murtaugh (talk | contribs) (→Turtle Graphics Inkscape Extension)
Turtle graphics refers to a technique of allowing graphics to be drawn, typically on a computer screen, by controlling a virtual "turtle" with simple commands like forward and turn. Turtle graphics were first described using the programming language LOGO, and were created by Seymour Papert as part of constructivist approach to teaching kids geometry by creating simulation environments or "microworlds", where principles could be approached and explored in a direct way, as opposed to classical formal education using pre-determined abstractions.
Turtle graphics are a kind of vector-based graphics system, in contrast to a traditional systems raster-based system like a bitmap.
http://www.greenteapress.com/thinkpython/swampy/
see Vector graphics
Prototyping Assignment
Create a drawing using set of cascading functions, as in the examples "arc, leaf, flower" or "building, city, starcity" worked through in class, and the exercises of Chapter 4 of Think Python.
Use the "Seymour" Inkscape extension to create a single SVG file containing your code + the resulting graphics arranged on the page.
Turtle Graphics Inkscape Extension
Installation
Unzip the two files contained in: File:Seymour.zip and copy them to ~/.config/inkscape/extensions[1]. Restart Inkscape if necessary.
Use
If properly installed, you should have a "Python" option in your Extensions menu. Select "Seymour..." to use the extension. Place your code in a text box on the SVG page and right-click the text to select "Object Properties" where you can set the id of the element to "code" (the value the Seymour extension expects).
Code
#!/usr/bin/env python
#-*- coding:utf-8 -*-
"""
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"""
import random, lxml, sys
sys.path.append('/usr/share/inkscape/extensions') # or another path, as necessary
import inkex
from simplestyle import *
#########################################################
# lxml utils
def collecttext (elt):
ret = elt.text or ""
ret += "\n".join([collecttext(child) for child in elt])
return ret
#def getcontents (element):
# return (element.text or "") + "".join(map(lxml.etree.tostring, element))
#########################################################
# the main turtle action
import math
defaultpathstyles = {
'fill':'none',
'fill-rule':'evenodd',
'stroke':'#000000',
'stroke-width':'1px',
'stroke-linecap':'butt',
'stroke-linejoin':'miter',
'stroke-opacity':'1'
}
def rgb (r, g, b):
return '#%02x%02x%02x' % (r,g,b)
# <path style="fill:none;fill-rule:evenodd;stroke:#000000;stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;stroke-opacity:1" d="%s" />
def pointstodata (points):
try:
data = "M %0.6f,%0.6f" % points[0]
for p in points[1:]:
data += " L %0.6f,%0.6f" % p
return data
except IndexError:
return ""
class Turtle (object):
def __init__(self, x=100.0, y=100.0, heading=0.0, pendown=False, layer=None):
self.x = x
self.y = y
self.heading = heading
self._pendown = pendown
self.points = []
self.stack = []
if layer is not None:
self.stack.append(layer)
self.styles = {}
def goto(self, x, y):
self.x = x
self.y = y
def face(self, d):
self.heading = (d/180.0)*math.pi
def forward (self, steps):
self.x += math.cos(self.heading) * steps
self.y -= math.sin(self.heading) * steps
if self._pendown:
self.points.append((self.x, self.y))
def left (self, d):
d = (d/180.0)*math.pi
self.heading += d
def backward (self, steps):
self.forward(-steps)
def right (self, d):
self.left(-d)
def backward (self, steps):
self.bk(steps)
def pendown (self):
self._pendown = True
self.points.append((self.x, self.y))
def penup (self):
self._pendown = False
if len(self.points) and len(self.stack):
path = inkex.etree.Element(inkex.addNS('path', 'svg'))
# http://stackoverflow.com/questions/1551666/how-can-2-python-dictionaries-become-1/1551878#1551878
styles = dict(defaultpathstyles, **self.styles)
path.set('style', formatStyle(styles))
path.set('d', pointstodata(self.points))
self.stack[-1].append(path)
self.points = []
def startgroup (self, id=None):
g = inkex.etree.Element(inkex.addNS('g', 'svg'))
if id is not None:
g.set('id', str(id))
self.stack[-1].append(g)
self.stack.append(g)
def endgroup (self):
self.stack.pop()
## aliases
def fd (self, steps): self.forward(steps)
def bk (self, steps): self.backward(steps)
def lt (self, d): self.left(d)
def rt (self, d): self.right(d)
def pd (self): self.pendown()
def pu (self): self.penup()
def export_to_dict (self, d):
d['forward'] = self.forward
d['backward'] = self.backward
d['left'] = self.left
d['right'] = self.right
d['pendown'] = self.pendown
d['penup'] = self.penup
d['goto'] = self.goto
d['face'] = self.face
d['startgroup'] = self.startgroup
d['endgroup'] = self.endgroup
d['fd'] = self.fd
d['bk'] = self.bk
d['lt'] = self.lt
d['rt'] = self.rt
d['pd'] = self.pd
d['pu'] = self.pu
d['styles'] = self.styles
#########################################################
# The Inkscape Effect interface
class SeymourEffect(inkex.Effect):
def __init__(self):
inkex.Effect.__init__(self)
# http://docs.python.org/lib/module-optparse.html
self.OptionParser.add_option('-c', '--codeid', action = 'store',
type = 'string', dest = 'codeid', default = 'code',
help = 'ID of code element')
def effect (self):
codeid = self.options.codeid
svg = self.document.getroot()
# svg = self.document.xpath('//svg:svg', namespace = inkex.NSS)[0]
code = self.document.xpath("//*[@id='%s']" % codeid)[0]
src = collecttext(code)
# print src
width = inkex.unittouu(svg.get('width'))
height = inkex.unittouu(svg.attrib['height'])
outputlayer = inkex.etree.SubElement(svg, 'g')
outputlayer.set(inkex.addNS('label', 'inkscape'), 'Seymour Output')
outputlayer.set(inkex.addNS('groupmode', 'inkscape'), 'layer')
turtle = Turtle(x=width/2, y=height/2, layer=outputlayer)
d = {}
turtle.export_to_dict(d)
d['rgb'] = rgb
exec src in d
##############################################################################
# This file can be directly applied to an SVG on the commandline using:
# python seymour.py path/to/your.svg
if __name__ == "__main__":
effect = SeymourEffect()
effect.affect()