Polygon drawing

Question

I want the user to define a polygon by using his mouse and clicks to define the points. The second task is once i have a set of defined polygons i want to check if some randomly generated points lie within any of those polygons.

I am working on C# .net platform. Thanks.

Answer 1

This is not a simple task. For instance, you should analyze and sort the set of points as Convex or Concave Hull. You can use the following links as resources:

http://ubicomp.algoritmi.uminho.pt/local/concavehull.html

http://marknelson.us/2007/08/22/convex/

Is there an efficient algorithm to generate a 2D concave hull?

http://courses.csail.mit.edu/6.854/06/scribe/s26-randomIC.pdf

http://softsurfer.com/Archive/algorithm_0109/algorithm_0109.htm

Answer 2

Old thread, but straight forward solution. This is actually pretty simple if you make full use of the Graphics and Drawing2D namespaces.

GraphicsPath.AddLines( Point[] )

Graphics.DrawPath( Drawing2D.GraphicsPath )

Graphics.FillPath( Drawing2D.GraphicsPath )

GraphcisPath.CloseFigure( )

So you'd simply create a new path, then call AddLines passing your array of points, and then call CloseFigure.

If you want to stroke it with a pen, use DrawPath. If you want to fill it with a brush, use FillPath.

Hit test for any points inside the polygon is simple as well, you would use Drawing.Region( Drawing2D.GraphicsPath ) and any overload of Region.IsVisible that allows you to specify a position and graphics object.