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[QUIZ] Turtle Graphics (#104)

 
 
Matthew Moss
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      12-02-2006
> People were most definitely drawing anti-aliased lines in mode 13h:
> http://freespace.virgin.net/hugo.eli...s/x_wuline.htm
>
> Aesthetically sensible when, as you say, each pixel is a visible rectangle? no.



Actually, it's exactly when you want anti-aliasing. If your pixels
were small enough, anti-aliasing would be unnecessary.

Of course, if your pixels are _very_ large, then yeah, I suppose it
won't help much. Maybe that's what you were getting at...

 
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Morton Goldberg
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      12-02-2006
On Dec 1, 2006, at 10:42 AM, Harold Hausman wrote:

> Ironically, I very recently implemented a turtle graphics system using
> GTK and Ruby.


Why ironic? I's say you have a head start on solving the quiz. I look
forward to seeing your submission.

> Here are some images that came from it to whet your appetite:
> http://www.danceliquid.com/images/LS/
>
> It used cairo for the anti-aliased line drawing.


Nice images. The design you call Penrose, I call Hilbert. That and
several other classic turtle designs (both the turtle code and the
graphic output) are included with the quiz for participants to test
against their Turtle class. The turtle code is in the samples folder
and the graphics (.tiff files) are in the designs folder. Also,
compare tree.tiff to your tree.png -- fairly similar.

Regards, Morton

 
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Morton Goldberg
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      12-02-2006
On Dec 1, 2006, at 7:22 PM, Edwin Fine wrote:

> /usr/local/lib/ruby/site_ruby/1.8/tk.rb:1187: warning: instance
> variable
> @encoding not initialized
>
> Is it something I am doing wrong, or some other problem? I don't know
> much about Tcl/Tk.


I'd look into this, but you aren't giving enough info for me to have
a clue as to how to reproduce it.

OTOH, since it's only a warning, it probably OK to let it go for now
unless you're seeing visible problems such as bad graphic output.
I've seen a number of harmless warnings both from Ruby/Tk and Tk
itself before.

Regards, Morton



 
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Edwin Fine
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      12-02-2006
Morton Goldberg wrote:
> On Dec 1, 2006, at 7:22 PM, Edwin Fine wrote:
>
>> /usr/local/lib/ruby/site_ruby/1.8/tk.rb:1187: warning: instance
>> variable
>> @encoding not initialized
>>
>> Is it something I am doing wrong, or some other problem? I don't know
>> much about Tcl/Tk.

>
> I'd look into this, but you aren't giving enough info for me to have
> a clue as to how to reproduce it.
>
> OTOH, since it's only a warning, it probably OK to let it go for now
> unless you're seeing visible problems such as bad graphic output.
> I've seen a number of harmless warnings both from Ruby/Tk and Tk
> itself before.
>
> Regards, Morton


Sorry I didn't provide more information earlier; I kind of assumed that
other people would have got the warnings, too. Although the warnings are
in fact harmless, and the graphics appear to be just fine, it's a bit
annoying when you get 27,690 warnings (that's right: 27 thousand plus
warnings). These consisted of the following two warnings:

/usr/lib/ruby/1.8/tk.rb:2313: warning: redefine encoding=
/usr/lib/ruby/1.8/tk.rb:2316: warning: redefine encoding

followed by 27,688 repetitions of this warning:

/usr/lib/ruby/1.8/tk.rb:1187: warning: instance variable @encoding not
initialized

All I did was run this command line:

ruby turtle_viewer.rb samples/tree.rb

The warnings occur for any run of turtle_viewer.rb.

Here's my Ruby version:

ruby 1.8.4 (2005-12-24) [x86_64-linux]

I'm running this on Ubuntu Edgy x86-64. But I get the same warning when
I run on a 32-bit RHEL3 system using Ruby 1.8.5, too.

I can't post my code (yet) because of the 48-hour deadline, but I can
tell you that it does not have the word "encoding" anywhere in it

I'll investigate further. I was just wondering if anyone else saw this.
Thanks.

--
Posted via http://www.ruby-forum.com/.

 
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Hidetoshi NAGAI
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      12-02-2006
From: Edwin Fine <(E-Mail Removed)>
Subject: Re: tk.rb warning in Turtle Graphics (#104)
Date: Sat, 2 Dec 2006 17:03:13 +0900
Message-ID: <(E-Mail Removed)>
> warnings). These consisted of the following two warnings:
>
> /usr/lib/ruby/1.8/tk.rb:2313: warning: redefine encoding=
> /usr/lib/ruby/1.8/tk.rb:2316: warning: redefine encoding
>
> followed by 27,688 repetitions of this warning:
>
> /usr/lib/ruby/1.8/tk.rb:1187: warning: instance variable @encoding not
> initialized


Don't worry about those. Those are no problem.

Redefinition of TclTkLib.encoding and encoding= depends on
the difference between using 'tcltklib.so' only and with 'tk.rb'.

@encoding is used to check the encoding of a string.
It depends that the value of non-initialized instance varible is nil.
Of course, if check the existence of the variable first,
the warning will be removed.
But then, checking a string to pass to a Tcl/Tk interpreter needs
two steps (check and refer).
Such check is called very frequently. So, I ignored the warning.
--
Hidetoshi NAGAI ((E-Mail Removed))

 
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Harold Hausman
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      12-02-2006
On 12/2/06, Morton Goldberg <(E-Mail Removed)> wrote:
> On Dec 1, 2006, at 10:42 AM, Harold Hausman wrote:
>
> > Ironically, I very recently implemented a turtle graphics system using
> > GTK and Ruby.

>
> Why ironic? I's say you have a head start on solving the quiz. I look
> forward to seeing your submission.
>


I guess 'coincidentally' would have been a better word.

Unfortunately, I have scant time for Ruby Quiz. The one (possibly
two?) submission I made was a total fluke. (

> > Here are some images that came from it to whet your appetite:
> > http://www.danceliquid.com/images/LS/
> >
> > It used cairo for the anti-aliased line drawing.

>
> Nice images. The design you call Penrose, I call Hilbert. That and
> several other classic turtle designs (both the turtle code and the
> graphic output) are included with the quiz for participants to test
> against their Turtle class. The turtle code is in the samples folder
> and the graphics (.tiff files) are in the designs folder. Also,
> compare tree.tiff to your tree.png -- fairly similar.
>


My implementation includes an L-system exploration library which can
feed instructions directly to the pen. (which is abstracted from the
turtle in my code)

The turtle (which is implemented using eval in a very straight forward
manner), and the L-system library, can both produce strings of
instructions for the pen. (the pen is capable of both cairo and
gtk::drawingarea drawing)

I pulled most of the L-systems I was drawing from fractint, actually,
because the my L-system library is nearly interface compatible with
it. So credit goes out to the crazy wizards who contributed L-systems
to fractint.

There's even the option of having the turtle generate a string of
instructions, which can then be further iterated on by the L-systems,
an option that has yet to be properly exploited.

With that said, the code is a dirty, voracious, sub-optimal, tightly
coupled, borderline embarrassing, pile of hack. (As most of my one
weekend personal projects are.) But maybe it would be interesting to
you or others.

I've put it online, feel free to grab it:
http://www.danceliquid.com/docs/turtlegraphics.zip

But no cheating on the quiz with it...

Regards,
-Harold

 
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Edwin Fine
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      12-02-2006
Hidetoshi NAGAI wrote:
> From: Edwin Fine <(E-Mail Removed)>
> Subject: Re: tk.rb warning in Turtle Graphics (#104)
> Date: Sat, 2 Dec 2006 17:03:13 +0900
> Message-ID: <(E-Mail Removed)>
>> warnings). These consisted of the following two warnings:
>>
>> /usr/lib/ruby/1.8/tk.rb:2313: warning: redefine encoding=
>> /usr/lib/ruby/1.8/tk.rb:2316: warning: redefine encoding
>>
>> followed by 27,688 repetitions of this warning:
>>
>> /usr/lib/ruby/1.8/tk.rb:1187: warning: instance variable @encoding not
>> initialized

>
> Don't worry about those. Those are no problem.
>
> Redefinition of TclTkLib.encoding and encoding= depends on
> the difference between using 'tcltklib.so' only and with 'tk.rb'.
>
> @encoding is used to check the encoding of a string.
> It depends that the value of non-initialized instance varible is nil.
> Of course, if check the existence of the variable first,
> the warning will be removed.
> But then, checking a string to pass to a Tcl/Tk interpreter needs
> two steps (check and refer).
> Such check is called very frequently. So, I ignored the warning.

-------------
Well, I found a bizarre and (to me) totally inexplicable way to get rid
of the warning. This is from the quiz turtle_view.rb file. Adding an
explicit return value (any value; I used nil) to the draw method gets
rid of the warning. WTF???

# Transform the turtle's track into TkcLine objects and add them to
the
# canvas' display list. This method expects a track to be an array of
# the form
# track ::= [segment, segment, ...]
# segment ::= [point, point, ...]
# point ::= [x, y]
# where x and y are floats.
def draw
@turtle.track.each do |seqment|
if seqment.size > 1
pts = seqment.collect { |pt| transform(pt) }
TkcLine.new(@canvas, pts)
end
end
nil # Adding this (or any return value) stops that @encoding
warning
end

I just dunno. Weird.

--
Posted via http://www.ruby-forum.com/.

 
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Morton Goldberg
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      12-02-2006
On Dec 2, 2006, at 4:28 AM, Edwin Fine wrote:

> Well, I found a bizarre and (to me) totally inexplicable way to get
> rid
> of the warning. This is from the quiz turtle_view.rb file. Adding an
> explicit return value (any value; I used nil) to the draw method gets
> rid of the warning. WTF???
>
> # Transform the turtle's track into TkcLine objects and add them to
> the
> # canvas' display list. This method expects a track to be an
> array of
> # the form
> # track ::= [segment, segment, ...]
> # segment ::= [point, point, ...]
> # point ::= [x, y]
> # where x and y are floats.
> def draw
> @turtle.track.each do |seqment|
> if seqment.size > 1
> pts = seqment.collect { |pt| transform(pt) }
> TkcLine.new(@canvas, pts)
> end
> end
> nil # Adding this (or any return value) stops that @encoding
> warning
> end
>
> I just dunno. Weird.


I'm just as mystified as you area as to why it works, but I'm glad
you found a work-around that turns off all the warnings.

Regards, Morton

 
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Benjohn Barnes
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      12-02-2006

On 1 Dec 2006, at 16:07, James Edward Gray II wrote:

> On Dec 1, 2006, at 9:42 AM, Harold Hausman wrote:
>
>> It used cairo for the anti-aliased line drawing.

>
> I tried to use the new pure Ruby PNG library to get anti-aliased
> line drawing in the quiz files, but that sucker is a bit broken.


In a bout of "why can't graphics be easy like it was on my BBC", I
proposed as ASCII art Turtle graphics ruby quiz I knocked up a
quick implementation (invoking code reuse (woo!) of some bits I had
left over from the earlier dungeon quiz), but the graphics were so
cheesy, I didn't want to inflict them on the community.


 
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Dema
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      12-04-2006
Here is my straight-to-the-point answer:

class Turtle
include Math # turtles understand math methods
DEG = Math:I / 180.0

attr_accessor :track
alias run instance_eval

def initialize
clear
end

attr_reader y, :heading

# Place the turtle at [x, y]. The turtle does not draw when it
changes
# position.
def xy=(coords)
raise ArgumentError if !coords.is_a?(Array) ||
coords.size != 2 ||
coords.any? { |c| !c.is_a?(Numeric) }
@xy = coords
end

# Set the turtle's heading to <degrees>.
def heading=(degrees)
raise ArgumentError if !degrees.is_a?(Numeric)
set_heading(degrees)
end

# Raise the turtle's pen. If the pen is up, the turtle will not
draw;
# i.e., it will cease to lay a track until a pen_down command is
given.
def pen_up
@pen_down = false
end

# Lower the turtle's pen. If the pen is down, the turtle will draw;
# i.e., it will lay a track until a pen_up command is given.
def pen_down
@pen_down = true
end

# Is the pen up?
def pen_up?
!@pen_down
end

# Is the pen down?
def pen_down?
@pen_down
end

# Places the turtle at the origin, facing north, with its pen up.
# The turtle does not draw when it goes home.
def home
pen_up
@xy = [0,0]
@heading = 0
end

# Homes the turtle and empties out it's track.
def clear
home
@track = []
end

# Turn right through the angle <degrees>.
def right(degrees)
set_heading(@heading + degrees)
end

# Turn left through the angle <degrees>.
def left(degrees)
set_heading(@heading - degrees)
end

# Move forward by <steps> turtle steps.
def forward(steps)
dx, dy = calc_delta(steps)
go [ @xy[0] + dx, @xy[1] + dy ]
end

# Move backward by <steps> turtle steps.
def back(steps)
dx, dy = calc_delta(steps)
go [ @xy[0] - dx, @xy[1] - dy ]
end

# Move to the given point.
def go(pt)
track << [ @xy, pt ] if pen_down?
@xy = pt
end

# Turn to face the given point.
def toward(pt)
@heading = atan(pt[0].to_f / pt[1].to_f) / DEG
end

# Return the distance between the turtle and the given point.
def distance(pt)
sqrt((@xy[0] - pt[0]) ** 2 + (@xy[1] - pt[1]) ** 2)
end

# Traditional abbreviations for turtle commands.
alias fd forward
alias bk back
alias rt right
alias lt left
alias pu pen_up
alias pd pen_down
alias pu? pen_up?
alias pd? pen_down?
alias set_h heading=
alias set_xy xy=
alias face toward
alias dist distance

private
def set_heading(degrees)
@heading = degrees % 360
end

def calc_delta(steps)
[ sin(heading * DEG) * steps,
cos(heading * DEG) * steps ]
end
end

Ruby Quiz wrote:
> The three rules of Ruby Quiz:
>
> 1. Please do not post any solutions or spoiler discussion for this quiz until
> 48 hours have passed from the time on this message.
>
> 2. Support Ruby Quiz by submitting ideas as often as you can:
>
> http://www.rubyquiz.com/
>
> 3. Enjoy!
>
> Suggestion: A [QUIZ] in the subject of emails about the problem helps everyone
> on Ruby Talk follow the discussion. Please reply to the original quiz message,
> if you can.
>
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>
> by Morton Goldberg
>
> [Editor's Note: You can download the files for this quiz at:
>
> http://rubyquiz.com/turtle.zip
>
> --JEG2]
>
> Turtle Graphics
> ===============
>
> Turtle graphics is a form of computer graphics based on the ideas of turtle
> geometry, a formulation of local (coordinate-free) geometry. As a brief
> introduction to turtle graphics, I quote from [1]:
>
> Imagine that you have control of a little creature called a turtle
> that exists in a mathematical plane or, better yet, on a computer
> display screen. The turtle can respond to a few simple commands:
> FORWARD moves the turtle in the direction it is facing some
> number of units. RIGHT rotates it clockwise in its place some
> number of degrees. BACK and LEFT cause the opposite movements. ...
> The turtle can leave a trace of the places it has been: [its
> movements] can cause lines to appear on the screen. This is
> controlled by the commands PENUP and PENDOWN. When the pen is
> down, the turtle draws lines.
>
> For example, the turtle commands to draw a square, 100 units on a side, can be
> written (in a Ruby-ized form) as:
>
> pen_down
> 4.times { forward 100; right 90 }
>
> For more information, see [2] and [3].
>
> This quiz is a bit different from most. If the usual Ruby quiz can be likened to
> an essay exam, this one is a fill-in-the-blanks test. I'm supplying you with a
> complete turtle graphics package, except -- to give you something to do -- I've
> removed the method bodies from the key file, lib/turtle.rb. Your job is to
> repair the damage I've done and make the package work again.
>
> Turtle Commands
> ===============
>
> There are quite a few turtle commands, but that doesn't mean you have to write a
> lot of code to solve this quiz. Most of the commands can be implemented in a
> couple of lines. It took me a lot longer to write a description of the commands
> than it did for me to implement and test all of them.
>
> I use the following format to describe turtle commands:
>
> long_name | short_name <arg>
> description ...
> Example: ...
>
> All turtle commands take either one argument or none, and not all turtle
> commands have both a long name and a short name.
>
> Required Commands
> -----------------
>
> These commands are required in the sense that they are needed to reproduce the
> sample designs. Actually, you could get away without implementing 'back' and
> 'left', but implementing them is far easier than trying to write turtle code
> without them.
>
> pen_up | pu
> Raises the turtle's pen. The turtle doesn't draw (lay down a visible
> track) when its pen is up.
>
> pen_down | pd
> Lowers the turtle's pen. The turtle draws (lays down a visible track)
> when its pen is down.
>
> forward | fd <distance>
> Moves the turtle forwards in the direction it is facing.
> Example: forward(100) advances the turtle by 100 steps.
>
> back | bk <distance>
> Moves the turtle backwards along its line of motion.
> back <distance> == forward -<distance>
> Example: back(100) backs up the turtle by 100 steps.
>
> right | rt <angle>
> Turns the turtle clockwise by <angle> degrees.
> Example: right(90) turns the turtle clockwise by a right angle.
>
> left | lt <angle>
> Turns the turtle counterclockwise by <angle> degrees.
> left <angle> == right -<angle>
> Example: left(45) turns the turtle counterclockwise by 45 degrees.
>
> Traditional Commands
> --------------------
>
> These commands are not needed to reproduce any of the sample designs, but they
> are found in all implementations of turtle graphics that I know of.
>
> home
> Places the turtle at the origin, facing north, with its pen up. The
> turtle does not draw when it goes home.
>
> clear
> Homes the turtle and empties out it's track. Sending a turtle a clear
> message essentially reinitializes it.
>
> xy
> Reports the turtle's location.
> Example: Suppose the turtle is 10 turtle steps north and 15 turtle steps
> west of the origin, then xy will return [-15.0, 10.0].
>
> set_xy | xy= <point>
> Places the turtle at <point>. The turtle does not draw when this command
> is executed, not even if its pen is down. Returns <point>.
> Example: Suppose the turtle is at [10.0, 20.0], then self.xy = [50, 80]
> moves the turtle to [50.0, 80.0], but no line will drawn between the [10,
> 20] and [50, 80].
>
> heading
> Reports the direction in which the turtle is facing. Heading is measured
> in degrees, clockwise from north.
> Example: Suppose the turtle is at the origin facing the point [100, 200],
> then heading will return 26.565 (approximately).
>
> heading= | set_h <angle>
> Sets the turtle's heading to <angle>. <angle> should be given in degrees,
> measured clockwise from north. Returns <angle>.
> Example: After self.heading = 135 (or set_h(135) which is easier to
> write), the turtle will be facing southeast.
>
> pen_up? | pu?
> Reports true if the turtle's pen is up and false otherwise.
>
> pen_down? | pd?
> Reports true if the turtle's pen is down and false otherwise.
>
> Optional Commands
> -----------------
>
> These commands are only found in some implementations of turtle graphics. When
> they are implemented, they make the turtle capable of doing global (coordinate)
> geometry in addition to local (coordinate-free) geometry.
>
> I used one of these commands, go, to draw the mandala design (see
> designs/mandala.tiff and samples/mandala.rb). If you choose not to implement the
> optional commands, you might try writing a turtle program for drawing the
> mandala design without using go. But, believe me, it is much easier to implement
> go than to write such a program.
>
> go <point>
> Moves the turtle to <point>.
> Example: Suppose the turtle is home (at the origin facing north). After
> go([100, 200]), the turtle will be located at [100.0, 200.0] but will
> still be facing north. If its pen was down, it will have drawn a line
> from [0, 0] to [100, 200].
>
> toward | face <point>
> Turns the turtle to face <point>.
> Example: Suppose the turtle is at the origin. After toward([100, 200]),
> its heading will be 26.565 (approximately).
>
> distance | dist <point>
> Reports the distance between the turtle and <point>.
> Example: Suppose the turtle is at the origin, then distance([400, 300])
> will return 500.0 (approximately).
>
> Interfacing to the Turtle Graphics Viewer
> =========================================
>
> Implementing turtle graphics without being able to view what the turtle draws
> isn't much fun, so I'm providing a simple turtle graphics viewer. To interface
> with the viewer, turtle instances must respond to the message track by returning
> an array which the viewer can use to generate a line drawing.
>
> The viewer expects the array returned by track to take the following form:
>
> track ::= [segment, segment, ...] # drawing data
> segment ::= [point, point, ...] # points to be joined by line segments
> point ::= [x, y] # pair of floats
>
> Example: [[[0.0, 0.0], [200.0, 200.0]], [[200.0, 0.0], [0.0, 200.0]]]
>
> This represents an X located in the upper-right quadrant of the viewer; i.e.,
> two line segments, one running from the center of the viewer up to its
> upper-right corner and the other running from the center of the top edge down to
> the center of the right edge.
>
> [Editor's Note: I added a script to dump your turtle graphics output to PPM
> image files, for those that don't have TK up and running. It works identically
> to Morton's turtle_viewer.rb, save that it writes output to a PPM image file in
> the current directory. For example, to output the included tree image, use
> `ruby turtle_ppm_writer.rb samples/tree.rb`. --JEG2]
>
> Unit Tests
> ==========
>
> I'm including the unit tests which I developed to test turtle commands. For the
> purposes of the quiz, you can ignore tests/turtle_view_test.rb. But I hope you
> will find the other test suite, tests/turtle_test.rb, helpful. It tests every
> one of the turtle commands described above as well as argument checking by the
> commands. Don't hesitate to modify any of the unit tests to meet the needs of
> your quiz solution.
>
> References
> ==========
>
> [1] Abelson, H. & A. diSessa, "Turtle Geometry", MIT Press, 1981.
> [2] Harvey, B., "Computer Science Logo Style", Chapter 10.
> http://www.cs.berkeley.edu/~bh/pdf/v1ch10.pdf
> [3] Wikipedia, http://en.wikipedia.org/wiki/LOGO_programming_language


 
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