#106 Can't union identical polygons where both PolyTypes as Subject

[Joseph Werick]

When you try to union two identical polygons (rectangles in this example) setting both as Subject , the solution polygon is null.

using Polygon = List<IntPoint>;
using Polygons = List<List<IntPoint>>;

public void run() {
Polygons subj = new Polygons(2);
subj.Add(new Polygon(4));
subj[0].Add(new IntPoint(30, 30));
subj[0].Add(new IntPoint(30, 250));
subj[0].Add(new IntPoint(250, 250));
subj[0].Add(new IntPoint(250, 30));

        subj.Add(new Polygon(4));
        subj[1].Add(new IntPoint(30, 30));
        subj[1].Add(new IntPoint(30, 250));
        subj[1].Add(new IntPoint(250, 250));
        subj[1].Add(new IntPoint(250, 30));

        Polygons solution = new Polygons();

        Clipper c = new Clipper();
        c.AddPaths(subj, PolyType.ptSubject, true);
        c.Execute(ClipType.ctUnion, solution);

}

[Angus Johnson]

Hi Joseph. There is no bug. Since you haven't specified a polygon fill type in the Execute method, it defaults to PolyFillType.pftEvenOdd. Consequently the second fill correctly erases the first. If you set the fill type to PolyFillType.pftNonZero you'll get the result you're expecting.

[Ignorant]

Angus,
does it mean that odd even filltype op s on the intersection of the
subject contours/paths.?
Mahesh naik

On Sat, Aug 30, 2014 at 2:37 AM, Angus Johnson angusj@users.sf.net wrote:

Hi Joseph. There is no bug. Since you haven't specified a polygon fill
type in the Execute method, it defaults to PolyFillType.pftEvenOdd.
Consequently the second fill correctly erases the first. If you set the
fill type to PolyFillType.pftNonZero you'll get the result you're expecting.

---

• [bugs:#106] http://sourceforge.net/p/polyclipping/bugs/106 Can't union
  identical polygons where both PolyTypes as Subject*

Status: open
Group:
Created: Fri Aug 29, 2014 07:56 PM UTC by Joseph Werick
Last Updated: Fri Aug 29, 2014 07:56 PM UTC
Owner:* nobody

When you try to union two identical polygons (rectangles in this example)
setting both as Subject , the solution polygon is null.

using Polygon = List<IntPoint>;
using Polygons = List<List<IntPoint>>;

public void run() {
Polygons subj = new Polygons(2);
subj.Add(new Polygon(4));
subj[0].Add(new IntPoint(30, 30));
subj[0].Add(new IntPoint(30, 250));
subj[0].Add(new IntPoint(250, 250));
subj[0].Add(new IntPoint(250, 30));

    subj.Add(new Polygon(4));
    subj[1].Add(new IntPoint(30, 30));
    subj[1].Add(new IntPoint(30, 250));
    subj[1].Add(new IntPoint(250, 250));
    subj[1].Add(new IntPoint(250, 30));

    Polygons solution = new Polygons();

    Clipper c = new Clipper();
    c.AddPaths(subj, PolyType.ptSubject, true);
    c.Execute(ClipType.ctUnion, solution);

}

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[Joseph Werick]

Thanks for your quick response, I understand now. Off to read more...