[MWForum]setbg and patterned backgrounds

[Clara Jackson]

It worked like a charm, thanks! I'm expecting a copy of the projects to
be sent to me in early March and I would be happy to post them online.
:o)

Thanks for all your help!
Clara

>>> wpetti@mathcats.com 02/19/03 12:00PM >>>
To undo a "setbg" command, just enter the command

setbg 0

(or use whatever color number you prefer).

This will not erase any graphics stamped on top of the background, but
it will restore the background to white.

As for how to create a patterned background, this can become a little
programming challenge for your students.  For instance, set the turtle's
shape to the desired shape for the pattern and position it in the top
left corner of the page, then write a procedure something like this
(adjusting the numbers depending on the turtle's size and your page
size):

to pattern
seth 90
repeat 9 [repeat 15 [fd 40 stamp]
          bk 15 * 40
          rt 90 fd 40 lt 90]
seth 90
end

I bet your students can program a rainbow, too, with a series of
half-circles of increasing size.  Set the turtle to a wide pen size,
such as

setpensize 60

It will take some experimenting to get it right, but that is a good
part of the fun.

If you wish to stamp other graphics on top of the background pattern
and then be able to erase those added graphics, be sure to freeze the
background pattern before you continue:

freezebg

Then "clean" or "cg" will erase the graphics added on top of this
background without erasing the background itself.

Wendy Petti