Markus Kuhn said:
For example, see the section "3.5 Direction of Paths" in
Adobe Type 1 Font Format http://partners.adobe.com/public/developer/en/font/T1_SPEC.PDF
Included polygons must be coded in counter-clockwise direction and excluded polygons clockwise.
In other words, as you draw the boundary of the polygon, "inside" is always "left" of the pen direction, and "outside" is always "right". Couldn't be simpler.
Actually, there are two common algorithms in use. Draw a line-segment (needn't be straight, but must avoid any place the polygon intersects itself) from point P to somewhere at infinity (in practice, well outside the boundaries of the shape). (1) P is "inside" if the line-segment crosses the polygon an odd number of times. (2) For each crossing, determine whether the polygon is going left-to-right or right-to-left (when looking along the line-segment from P). P is "inside" if there are different numbers of crossings of each type. It looks like Adobe are using the second. However, I suspect the first will be better in this use. For an example of the difference, consider the shape: +---+ | | +---+---+---+ | | A | | | +---+---+ | | +-------+ In algorithm 1, area A is "outside". In algorithm 2, it is "inside". -- Clive D.W. Feather | Work: <clive@demon.net> | Tel: +44 20 8495 6138 Internet Expert | Home: <clive@davros.org> | Fax: +44 870 051 9937 Demon Internet | WWW: http://www.davros.org | Mobile: +44 7973 377646 Thus plc | |