[Squeakland] Pen Trails and Sensors

[Jeff Longland]

I'm a new Squeak user and I'm not trying to tackle anything too difficult at
the moment, or at least I didn't think so initially.  I'm working on
creating an object (a snake) that will travel along the edge of a rectangle
while leaving a trail.  As the snake works around the rectangle and comes
back to its starting point, the snake will view the existing trail as the
new wall - making smaller and smaller rectangles, until the snake has
covered the surface area of the rectangle.  Ideally, I'd like to be able to
move the snake object into any shape and it will cover the surface area in
the same manner as the above mentioned rectangle.  I've been using penDown
to create a pen trail behind the snake, but my major problem is that the
sensor on my object is unable to view the pen trail.  I've searched around
quite a bit and I've seen mention of transparent playfields, adjusting the
display depth, and a method that refreshes the playfield - but Squeak
documentation seems to be somewhat scattered.  I've been playing with Squeak
for a while now, and I'm slowly getting the hang of everything - but it's
taken quite a while.  Does anyone have any suggestions on how I can make the
pen trails visible to my sensor?  Or any other suggestions for the project
and my journey through Squeak?

Thanks!
Jeff