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From: datpete@daimi.aau.dk (Peter Andersen)
Newsgroups: comp.sys.mac.programmer,comp.graphics
Subject: Fill rules on the Mac
Message-ID: <1990Nov28.154948.23415@daimi.aau.dk>
Date: 28 Nov 90 15:49:48 GMT
Sender: datpete@daimi.aau.dk (Peter Andersen)
Reply-To: datpete@daimi.aau.dk (Peter Andersen)
Organization: DAIMI: Computer Science Department, Aarhus University, Denmark
Lines: 43

We are porting an advanced graphics system to the Mac.

The graphics system supports two different fill rules for
polygons: even-odd and zero-winding. The difference between
the two fill rules can be seen when you make the following
polygon

    |-------------|
    |             |
    |             |
    |    |---|    |
    |    |   |    |
    |----|---|    |
	 |        |
	 |--------|
  
    Even-odd fill rule	     Zero-winding fill rule
    |-------------|	     |-------------|
    |*************|	     |*************| 
    |*************|	     |*************|
    |****|---|****|	     |****|---|****|
    |****|   |****|	     |****|***|****|
    |----|---|****|	     |----|---|****|
	 |********|		  |********|
	 |--------|		  |--------|
  
    Note: the rectangle      Note: the rectangle in
    in the middle is NOT     the middle IS filled
    filled

As far as we can see the Mac only uses even-odd fillrule
when determining what is inside and outside of a polygon
(or a region for that matter).

Now to the question:
Does anybody know of a way to simulate the zero-winding
fill rule on the Mac, short of implementing your own
scan-algorithm?!


Any clues are appreciated!

/Kim, Jorgen & Peter.