[Ipe-discuss] Position of a Mark

[Ernst Schrewe]

Hi,
I recently started to learn writing Ipelets with Lua. My ultimate goal
is to be able to create an Ipelet that draws the visibility polygon for
a given point

https://en.wikipedia.org/wiki/Visibility_polygon

The starting point would obviously be, that I place a selection of given
polygons and one Mark on the canvas. The Mark represents the point, from
which the visibilty of the surrounding areas shall be calculated.

And when my (future) Ipelet is launched, it should retrieve the
coordinates of all these selected polygons and the Mark and then do the
calculations, etc.


But I am currently struggling with retrieving the coordinates of a Mark
from within a purely Lua-based Ipelet.

Apparently a Mark has a designated type "reference" in Lua. The manual
states that this data type is quite different from regular path objects,
but unfortunately does not go into further details.

I would be very grateful for any hints or advice on what attributes
and/or methods can be utilised on this kind of data type.

Thanks in advance and

best regards

Ernst