[OpenJDK 2D-Dev] <AWT Dev> Question: Area changes order of points

[Jim Graham]

Note that "Area" is specifically targeted to processing areas, not 
outlines.  While it does express its answer in the form of an outline, 
on the other hand the information it is processing, operating on, and 
representing internally is areas, not outlines.  It's output is intended 
only for filling, not for stroking.  You can stroke its output because 
the graphics system allows you to stroke any path, but the Area class 
wasn't concerned at all about stroking issues (such as path direction) 
during its internal operations.

If you are simply trying to simplify the polygon to throw out 
unnecessary segments to simplify rendering then the Area class is not 
designed or optimized to address your needs.  Additionally, it is doing 
way more work than your application needs and writing your own 
implementation may perform better.

Also, Area will perform optimizations that you don't want such as 
removing an interior segment that does not contribute to the boundary 
between interior and exterior.  Such segments are superfluous for 
filling, but might be visible when stroking.  The Area class won't care 
and will just delete them all the same because it only cares about areas 
internally.

Another issue to consider is that if you have arrows or other periodic 
decorations then removing segments will mean that those decorations will 
shift their locations.  The length of the omitted path must be 
considered while computing where the decorations are placed, but if you 
pre-edit the path to remove them then those lengths cannot be computed.

Out of curiosity, are you trying to clip these paths to avoid having to 
process decorations on parts of the path that are far outside of the 
clip?  We've recently discussed that performance issue internally in the 
Graphics-Rasterizer project and noted that it is an opportunity for 
future performance work...

			...jim

On 10/7/15 12:37 AM, Hruda, Steve wrote:
> Hi Jim,
> we are using the Area to clip/intersect geometries like a polygon. Such a polygon has a digitizing direction and this direction has an effect on the point order.
>
> If we visualize a clipped polygon in our map, than we have the problem that complex line styles like a placed graphic along a line e.g. an arrow, shows in the wrong direction.
>
> Thanks for the explanation Jim, I will consider the point-order manipulation in our application.
>
> Regards,
> Steve
>
>
>
>
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> -----Original Message-----
> From: Jim Graham [mailto:james.graham at oracle.com]
> Sent: Tuesday, October 6, 2015 8:38 PM
> To: Hruda, Steve <steve.hruda at hexagongeospatial.com>
> Cc: Sergey Bylokhov <Sergey.Bylokhov at oracle.com>; 2d-dev <2d-dev at openjdk.java.net>
> Subject: Re: [OpenJDK 2D-Dev] <AWT Dev> Question: Area changes order of points
>
> Hi Steve,
>
> Area simplifies the shape into a normalized version that defines the same interior area.  It does not care what the original ordering of the points was as it internalizes the shape, all it cares about is which areas are geometrically inside vs. outside and it creates a path according to its own internal policies that defines the same inside/outside boundaries.
>
> There is no "trick" to customizing this behavior and I'm not entirely sure why the point ordering would matter when you are performing CAG (Constructive Area Geometry) operations - only interiors and exteriors should matter.
>
>                          ...jim
>
> On 10/5/15 8:19 AM, Sergey Bylokhov wrote:
>> Hello,
>> I think this question is related to java2d, correct alias cc.
>>
>> On 24.09.15 12:53, Hruda, Steve wrote:
>>> I use the java.awt.geom.Area class to clip a shape. Today I noticed
>>> that new Area(Shape) changes the orientation of the shape, so that I
>>> get the points of the Area counter-clockwise in every case.
>>>
>>> The following test shows you my problem.
>>>
>>> https://drive.google.com/file/d/0B7P_rknS1TWxVGJ6a3hBaElBTk0/view?usp
>>> =sharing
>>>
>>>
>>> Is this a bug or do I something wrong?
>>>
>>> Is there a trick to get the points in the correct order?
>>
>>
>