On Tue, Jun 19, 2018 at 10:40 AM, Andre Roberge <andre.robe...@gmail.com> wrote:
> HI, > > There seems to be a lot of misunderstanding about this issue. Hopefully, > the following can help clear it up. > > 0. The turtle module includes functions named left() and right() which > result in the turtle rotating in the corresponding direction on the screen. > 1. The turtle implementation includes a function, setworldcoordinates(), > which allows one to have user-defined coordinates (both for the width and > height of the world) including a choice as to which in which direction the > coordinates are increasing. The issue has nothing to do with what choice > is "best"; any user is free to use whatever they want. > 2. In the current implementation, if one choses some particular > orientation for the coordinates, the role of left() and right() are > inverted and no longer correspond to what the user sees on the screen. > > The submitted fix simply ensures that, no matter what one chooses for the > world coordinates via setworldcoordinates, when right() is called in a > program, the turtle turns right and not left. > Thank you for the clarification. I was just ranting about my pet peeve^^ Left and right should be consistent with the actual direction the turtle turns, from the POV of the turtle, yes. (Does it involve changing the "heading" of the turtle?) > André > > > On Tue, Jun 19, 2018 at 2:29 PM Yoshiki Ohshima <yoshiki.ohsh...@acm.org> > wrote: > >> I also stick my nose here. >> >> The notion of "in computer graphics Y goes down" is not as true as some >> people think. The graphics you are looking at right now on your computer >> most likely to have gone through some programs that use "Y goes up" scheme >> (such as GLSL). >> >> Only if you are talking about pixels and raster graphics, you could say >> that there is a dominant convention to make Y go down, but in with vectors, >> there is no such dominance. >> >> For end-users, why does it matter how actually pixels are stored in the >> actual memory? Computer is medium that can simulate anything; so the >> decision should not be based on what computer does at the lower levels. >> >> Once we leave from what computer does at low-level, there are math text >> books, which are dominantly "Y-up". Why do they have to know two different >> conventions? Unless, of course, learning the fact that the coordinate >> system is just a convention and can be different. >> >> Also there may be a case where the particular turtle graphics >> implementation is tied to the lower level pixel representation. But is >> basically mixing different abstraction levels, and unless you want to teach >> about mixing abstraction levels, it is a bad starting point. >> >> In summary: the statement "in computer graphics Y goes down" is a wrong >> argument for turtle graphics to use Y-down coordinate system. Then, for >> turtles and for end-users, there is an existing convention to make Y go >> down. So that should be a better default. >> >> >> >> >> On Mon, Jun 18, 2018 at 9:54 AM, Kevin Cole <kevin.cole@ >> novawebdevelopment.org> wrote: >> >>> Sticking my nose in where it don't belong. ;-) But that's never stopped >>> me before. ;-) >>> >>> First "I are not a teacher". At least, not in any formal sense of the >>> word. Second, some would say "I are not a programmer". I don't listen to >>> those people. >>> >>> In spite of the common "in computer graphics Y goes down", does that >>> make sense to new learners? I've gotten used to various coordinate systems, >>> but the first time I had to work with graph paper and plotting (and, for >>> that matter, maps) one goes "up" ("north", "forward") for Y. Then again, >>> maybe the average learner isn't quite as flexible these days, and telling >>> them after they've gotten used to a system that they have to flip >>> everything upside down and backwards isn't a great idea. I attribute my own >>> flexibility not to any innate ability but rather to learning during a time >>> when architectures OS's and languages were changing fast enough that there >>> wasn't time to become set in one's ways. >>> >>> [Note: Grammatical "mistakes" above are meant as weak -- very weak -- >>> humor. At least, most are.] >>> -- >>> *Kevin Cole* >>> <http://novawebdevelopment.org> >>> NOVA Web Development Co-Op >>> http://novawebdevelopment.org/ >>> Arlington, VA >>> >>> _______________________________________________ >>> Edu-sig mailing list >>> Edu-sig@python.org >>> https://mail.python.org/mailman/listinfo/edu-sig >>> >>> >> >> >> -- >> -- Yoshiki >> >> _______________________________________________ >> Edu-sig mailing list >> Edu-sig@python.org >> https://mail.python.org/mailman/listinfo/edu-sig >> > > _______________________________________________ > Edu-sig mailing list > Edu-sig@python.org > https://mail.python.org/mailman/listinfo/edu-sig > > -- -- Yoshiki
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