Answered
hello there.
Take this, for instance: https://www.geogebra.org/cl...
I'd like it to be "contained" inside a box - let's say -2<x<2, 0<y<4 - and off white outside.
In general, can I use tracing to fill a polygon or a circle?
Thanks for your help
The same question 
I would work with two points. First a free draggable point A, then a second point AA = A. You can show the trace of AA (not of A) and in the condition to show AA fill in the area which you want to fill in. So while dragging A the trace (of AA) will just fill in the defined area.
chris
There are various ways to do it. Maybe this is the easiest (white rectangle with inverse fill in a higher layer)https://www.geogebra.org/m/A71fBM86
could be like the file
potrebbe essere comeil file
You have a animated <line> and a <area> (polygon, conic, etc.). This 2 object intersect in 0..n points (l1)
Always complete pairs (l2) of these points builds Segments (l3), which lie within the <area>.
There are 0..n segments depending on the situation, which are advantageously kept in a list (l3).
This list (l3) is given the property Trace.
.
l1 = RemoveUndefined({Intersect(<line> <area>)})
l2 = First(l1, floor(Length(l1) / 2) * 2)
l3 = Sequence(Segment(l2(n), l2(n + 1)), n, 1, Length(l2) - 1, 2)
thank you all for the contributions
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