Paths - gEDA Scheme Reference Manual 1.8.1

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2.2.8 Paths

Paths are arbitrary shapes comprised of straight lines and Bézier curves. Each path contains a sequence of path elements, each of which requires zero or more absolute position parameters. The element types supported by gEDA are:

‘moveto’ elements represent a step (without drawing) to another point in the schematic, and begin a new subpath. ‘moveto’ elements need a single position parameter, which is the position of the endpoint of the move.
‘lineto’ elements draw a straight line from the current point to the point specified by a single position parameter.
‘curveto’ elements draw a Bézier curve from the current point. The curve requires three position parameters: the position of the first control point; the position of the second control point; and the endpoint of the curve.
‘closepath’ elements close the current subpath by drawing a straight line from the current point to the subpath's initial point. They take no parameters.

— Function: path? object

Returns ‘#t’ if and only if object is a path object.

— Function: path-length path

Returns the number of path elements in path.

— Function: path-ref path K

Returns the Kth element in path. The return value is a list. The first item in the list is a symbol indicating the type of element, and any additional items are the position parameters of the element. For example, a call to path-ref might return:
          (curveto (800 . 525) (700 . 700) (500 . 700))
If K is not a valid offset into path, raises an ‘out-of-range’ error.

— Function: path-remove! path K

Removes the Kth element in path, returning path. If K is not a valid offset, raises an ‘out-of-range’ error.

— Function: path-insert! path K type [positions...]

Inserts a new element into path at index K. type is a symbol indicating the type of element to insert, using the parameters positions. If K is less than zero or greater than the number of elements path already contains, the new element is appended to the path. For example, to append a straight line section to the current path:
          (path-insert! path -1 'lineto '(500. 100))