W3C home > Mailing lists > Public > www-svg@w3.org > May 2002

Re: fill-rule problem ..

From: Craig Brown <cmb@research.canon.com.au>
Date: Mon, 06 May 2002 11:21:50 +1000
To: "Goessner / MecXpert" <goessner@mecxpert.de>
Cc: "Craig Brown" <cmb@research.canon.com.au>, <www-svg@w3.org>
Message-Id: <20020506005558.60C6E8B10@bellmann.research.canon.com.au>
Stefan,

If you draw the path once, then a second time reversed - each time you cross
the resultant double-lines you get a no-op - and no fill will be performed.

...cmb


--Original Message--:
>hi craig,
>
>> Lads,
>>
>> The problem with all this stuff is the implementation.
>>
>> Imaging the situation where you have a U...
>>
>> Do you fill inside the U?
>>
>> If the answer is NO - think about the case where the top of the U touch.
>> Now - do you fill?  I assume the answer for a proposed "always" fill is
>> YES.
>>
>> Glitch is now you can't do scan-line rendering.  A scanline at the top of
>> the U effects the result for a scanline in the middle of the U.
>
>.. hmm .. i believe i understand.
>with scan-line rendering, i.e. drawing a ray from any point on the canvas to
>infinity in any direction and counting the number of path segments that the
>ray crosses, we cannot implement an fill-rule="always".
>
>> In reality - it is usually very easy to modify the content to get the
>effect
>> required rather than adding 2d complexity to filling.
>
>so an ever working method would be, to draw the U (or any open shape) *and*
>draw it reverse again back to its subpath initial point. then - with both
>rules 'evenodd' and 'nonzero' - the cross-counting works reliable, since the
>segments were counted twice.
>
>based on these thoughts following algorithm should be quite easy to
>implement:
>
>1) don't close open subpathes automatically.
>2) count closed subpath segments once and open subpath segments twice - with
>different directions.
>
>what do you think?
>--
>stefan goessner
>
>> ...cmb
>>
>> --Original Message--:
>> >It occurred to me that it might be useful to be able to specify more than
>> >one color for fill, to alternate the color according to different
>> >fill-rules. For instance:
>> >
>> ><polygon points="100,20 165,196 26,87 176,87 42,198 " style='stroke:blue;
>> >fill:yellow,blue; fill-rule:evenodd;'/>
>> >
>> >would give a star with yellow arms and a blue center.
>> >
>> >This might also be used to completly fill an enclosed area, by specifying
>> >the same color twice.
>> >
>> >Just an idea-
>> >-Doug
>> >
>> >
>> >> -----Original Message-----
>> >> From: www-svg-request@w3.org [mailto:www-svg-request@w3.org]On Behalf
>Of
>> >> Goessner / MecXpert
>> >> Sent: Friday, May 03, 2002 4:46 AM
>> >> To: www-svg@w3.org
>> >> Subject: Re: fill-rule problem ..
>> >>
>> >>
>> >> A solution to this problem might be an additional fill-rule, perhaps
>> >>
>> >> fill-rule="always"
>> >>
>> >> --
>> >> stefan
>> >>
>> >>
>> >>
>> >> > i simplified the path to a square with a "V" in it.
>> >> >
>> >> > <svg width="300" height="200">
>> >> >   <path id="A" transform="translate(20,20)" stroke-width="2"
>> >> stroke="blue"
>> >> > fill="lightgray" fill-rule="nonzero"
>> >> >         d="M0,0 H100 V100 H0 Z M10,50 50,90 90,50" />  <!-- clockwise
>/
>> >> > counterclockwise -->
>> >> >   <path id="B" transform="translate(140,20)" stroke-width="2"
>> >> stroke="blue"
>> >> > fill="lightgray" fill-rule="nonzero"
>> >> >         d="M0,0 H100 V100 H0 Z M90,50 50,90 10,50" />  <!-- clockwise
>/
>> >> > clockwise -->
>> >> > </svg>
>> >> >
>> >> > 1) if a (sub)path is not closed, an invisible closepath from the
>> >> (sub)path's
>> >> > current point to its initial point is used for filling.
>> >> > 2) if one path contains the other completely the fill-rule determines
>if
>> >> the
>> >> > subpath has to be filled or not.
>> >> > 3) fill-rule="nonzero" (the default) will
>> >> >    a) fill the inner subpath, if it has the same (angular) direction
>as
>> >> the
>> >> > outer subpath.
>> >> >    b) not fill the the inner subpath, if its angular direction is
>> >> different
>> >> > to the outer subpath's.
>> >> > 4) fill-rule="evenodd" will never fill the inner subpath
>> >> >
>> >> >
>> >> > it is conform to the SVG 1.1 spec, that there is *no way* to fill the
>> >> square
>> >> > in path (id="A") completely.
>> >> > the path can be modified (id="B")to match point 3a) above. But
>> >> in case of
>> >> an
>> >> > "N"-shaped subpath instead of a "V" that wouldn't help either.
>> >> > --
>> >> > stefan
>> >> >
>> >> >
>> >> > ----- Original Message -----
>> >> > From: "Doug Schepers" <doug@schepers.cc>
>> >> > To: "Goessner / MecXpert" <goessner@mecxpert.de>
>> >> > Sent: Wednesday, May 01, 2002 2:24 PM
>> >> > Subject: Re: fill-rule problem ..
>> >> >
>> >> >
>> >> > > Could this be a bug in ASV3?  I got it to render as solid once,
>after
>> >> > > refreshing a couple of times, and once got a blue artifact
>> >> line straight
>> >> > > from (50,50) to (90,50). [WinMe/IE6/ASV3]
>> >> > >
>> >> > > What is the logic behind it not filling the square with gray? No
>lines
>> >> are
>> >> > > being crossed. Do I misunderstand the fill rule?
>> >> > >
>> >> > > -Doug
>> >> > >
>> >> > > ----- Original Message -----
>> >> > > From: "Goessner / MecXpert" <goessner@mecxpert.de>
>> >> > > To: <www-svg@w3.org>
>> >> > > Sent: Wednesday, May 01, 2002 5:48 AM
>> >> > > Subject: fill-rule problem ..
>> >> > >
>> >> > >
>> >> > > > i have a simple square with two quadratic bezier segments
>> >> in it. it is
>> >> > > easy
>> >> > > > to define this by a single path element.
>> >> > > >
>> >> > > > <svg>
>> >> > > >   <path transform="translate(20,20)" stroke-width="2"
>stroke="blue"
>> >> > > > fill="lightgray"
>> >> > > >         d="M0,0 H100 V100 H0 Z M10,50 Q30,30 50,50 T90,50" />
>> >> > > > </svg>
>> >> > > >
>> >> > > > but i cannot find a fill-rule to completely fill the
>> >> square. even the
>> >> > new
>> >> > > > winding-count rule wouldn't work.
>> >> > > >
>> >> > > > --
>> >> > > > stefan goessner
>> >> > > >
>> >> > > >
>> >> > >
>> >> >
>> >>
>> >>
>> >
>> >
>> >
>> >
>> --
>> Craig Brown      Principal Software Engineer
>> Canon Information Systems Research Australia     Phone: 61 2 9805 2649
>> 1 Thomas Holt Drive,  North Ryde,  NSW 2113.     Fax:   61 2 9805 2929
>>
>
>
>
>
--
Craig Brown      Principal Software Engineer
Canon Information Systems Research Australia     Phone: 61 2 9805 2649
1 Thomas Holt Drive,  North Ryde,  NSW 2113.     Fax:   61 2 9805 2929
Received on Sunday, 5 May 2002 21:22:04 GMT

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