Re: LOGO-L> Re: MSWLogo

[George Mills <mills@softronix.com>]

An "erasing" pen can be up or down just like all other pen "tips".
It appears that your other logo's cancel the "Penerase" on the PD
command. Why not let the user stay in control and only remove the
"penerase" state when told to do so with PENPAINT.

A pen can:

Draw in SETPENCOLOR color (PENPAINT) if PD.
Draw in SETSCREENCOLOR color (PENERASE) if PD.
Draw in Reverse of Screen color (PENREVERSE) if PD.

PD had no "side effects".

For example if you wrote a complex set of procedures which included
PU's and PD's and you later wanted to call it again to erase it all you
have to do is say PE and run it again. If PD had side effects then you'd
have to modify that complex set of procedures to simply erase it.

Please join logo-l mailing list (See my web page on how to join) and
we can see what others think.

Wing K. Au wrote:
> 
> Dear George,
> 
> Yes I am aware of the use of these two commands as I have been using Logo
> for some 15 years.  However, the set of commands below should produce a line
> after the second last command has put the pen down (with all the other
> versions of Logo that I have used over the years).  I do not seem to be able
> to produce a line using MSWLogo using this set of commands.  Have I missed
> something?  By the way, I have tried this set of commands on a number of
> machines using MSWLogo (including the 16-bit and 32-bit versions).  If you
> have a moment to try these commands out on your machine and let me know of
> the outcome I would be most grateful.  Thanks again.  Sorry about keep
> pestering you.
> 
> Regards,
> Wing.
> 
> At 09:22 14/05/97 -0400, you wrote:
> >PE is Penerase (basically the color of the background)
> >PX is PenReverse (inverts the background)
> >
> >Wing K. Au wrote:
> >>
> >> Dear George,
> >>
> >> Thanks for the prompt reply.  The problem(s?) that we encountered could be
> >> highlighted by the following commands.
> >>
> >> cs
> >> fd 100
> >> pe
> >> bk 100
> >> pd
> >> fd 100
> >>
> >> We had no problem drawing a line and then erased a line.  However, when we
> >> put the pen down and tried to draw another line, the turtle did not draw a
> >> line with the last fd 100 command.  Did not miss something somewhere?
> >>
> Dr Wing Au,                              e-mail: wing.au@unisa.edu.au
> Senior Lecturer in Education Computing,  voice: +61 8 83024543
> Chair, Faculty IT Committee,             fax:   +61 8 83024536
> School of Education (Magill),
> University of South Australia,
> St Bernard's Road,
> Magill, SA 5072,
> Australia.

-- 
===============================================================
George Mills (mills@softronix.com)
http://www.softronix.com/
The www page contains some very powerful educational software.
Our single most important investment is our kids.

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