Hi Andreas,
Andreas Neumann <neumann@karto.baug.ethz.ch> wrote on 06/09/2006 03:00:57
PM:
> >>Rect:
> > A couple of comments on this.
> > 1) The shape described is really a hole (the area of the shape
> > is negative, given the SVG coordinate system). It should
> > go counter clock wise.
>
> can you explain why this is important here? Does the direction matter
> for basic shapes?
This is a little like asking, why do we use positive numbers instead
of negative numbers. If you just negate everything it works, right?
From a mathematical point of view I think it is very odd to specify
your basic shapes such that they have negative area. This also means
that the winding count for the interior of the basic shapes is negative
rather than positive.
If the whole world buys into this system then there are probably no
problems but when you consider things like vector effects where basic
shapes can now be used/combined with other shapes I think you are
likely to generate confusion among users. Like for boolean operations
if you intersected a primitive rect with another 'properly defined'
shape you would likely end up with the portion of the shape outside
of the rect (it might be possible so force implementations to
'normalize' shapes according to winding rule before boolean
operations).
This also could lead to missing or extra holes when paths are
combined because folks are likely to be surprised that the primitive
shapes decrement winding count rather than increment.
In the end I suspect it will be viewed as short sighted to go
"against the math" just because people would rather have shapes
go clockwise.

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