How do we draw the solution of an offset polygon (inflated polygon), which was created by the Clipper Library (C#)? Use method DrawPolygons()?

Question

I downloaded the clipper library, which allows me to inflate a polygon (offset a polygon).

"boundary_Points" is the Point array containing all vertices of the polygon. Below is the code I'm using. Unfortunately, the command "DrawPolygons()", which is used in other web examples, doesn't exist as a function. Is there any way to access this command or another way to draw? The challenge is: Clipper library uses the type IntPoint, which cannot be used in GDI+, as far as I'm concerned. Thanks

            using Path = List<IntPoint>;
            using Paths = List<List<IntPoint>>;
            
            boundary_path.AddLines(boundary_Points);
            Region boundary_region = new Region(boundary_path);
            g.DrawPath(pen1, boundary_path);                
            ClipperOffset co = new ClipperOffset();
            Path boundary_point_list= new Path(); //contains all IntPoints of the polygon
            co.AddPath(boundary_point_list, JoinType.jtRound, EndType.etClosedPolygon);
            Paths solution = new Paths();   // 
            co.Execute(ref solution, -7.0);
            DrawPolygons(solution, 0x40808080);
            g.FillPolygon(Brushes.Olive, boundary_Points);

score 1 · Accepted Answer · answered Jun 03 '22 at 09:39

Clipper does not provide drawing methods out-of-the-box. You'd have to convert IntPoint to whatever format suitable for drawing manually by the drawing API that you'd like to use.

I don't use C#, but here's what I do in my code in order to convert IntPoint to float-based type in C++:

void scale_down_polypaths(const Paths &p_polypaths_in, Vector<Vector<Point2>> &p_polypaths_out) {
    p_polypaths_out.clear();

    for (int i = 0; i < p_polypaths_in.size(); ++i) {
        const Path &polypath_in = p_polypaths_in[i];
        Vector<Vector2> polypath_out;

        for (int j = 0; j < polypath_in.size(); ++j) {
            polypath_out.push_back(Point2(
                    static_cast<real_t>(polypath_in[j].X) / SCALE_FACTOR,
                    static_cast<real_t>(polypath_in[j].Y) / SCALE_FACTOR));
        }
        p_polypaths_out.push_back(polypath_out);
    }
}

The result could then be passed to the drawing API, but again, it depends on what kind of library you use. I don't have experience with GDI+.

Thank you, I will try to look if I can do something similar in C#. But the problem I'm facing is, that I can not even access the values of the "Paths" object, therefore I can't run the for-loops to convert. — Martin Graupner, Jun 03 '22 at 16:35

How do we draw the solution of an offset polygon (inflated polygon), which was created by the Clipper Library (C#)? Use method DrawPolygons()?

1 Answers1