[Edu-sig] turtle coordinates: Y increase downards - as in most graphics API?

[Kevin Cole]

On Tue, Jun 19, 2018 at 1:40 PM, Andre Roberge <andre.roberge at 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.
>
> André
>

​Ah. Then I did indeed misunderstand the point. And now I'm of two minds as
to whether or not the fix is a fix. I see it as an option, but I also see
the argument that sprites, avatars, turtles, etc, often are designed with a
"head" and a "tail". So, it's back to the whole "stage left" vs. "left"
argument: Are we talking about the virtual creature's left or the viewer's
left? (Or am I misunderstanding yet again? If I'm not misunderstanding, I
would say "Make it a configuration or startup option, or attribute of
setworldcoordinates, or some such." For me, if I'm giving you directions to
my apartment, and say in e-mail "Turn left" I would expect you to turn to
your left, even if you knew which direction I was currently facing. I would
expect an avatar to turn to its left regardless of my viewing angle.)​


-- 
*Kevin Cole*
<http://novawebdevelopment.org>
NOVA Web Development Co-Op
http://novawebdevelopment.org/
Arlington, VA
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