August 30, 2008 01:13am pdt

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04.11.2008 at 05:48PM PDT, ID: 23316788

	[x] Attachment Details

Rotate a 2D polygon in C#

Asked by dsmclaughlin in Microsoft Visual C#.Net, Game Programming, Math & Science Questions

Tags: C#, .NET, Visual Studio

Hi,

I am in the process of writing a piece of code that will rotate a polygon (in C# a Point[]) I found an example here http://www.codeguru.com/forum/showthread.php?t=346093 (4th post) and tried to recreate it in C# (see attached code Snippet).

This code works to a certain degree, however I have two problems with it:

1) The polygon does rotate but not by the angle specified.

2) The polygon seems to shrink as it rotates.

The effect of calling rotatePolygon can be seen in the attached image. The red point is the point around which the polygon is being rotated.

My maths is not good enough to try and figure out why this isn't working so any advice on how to tweak this method is very much appreciated!

Many thanks

DrewStart Free Trial

         
           
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             public Point[] rotatePolygon(Point[] polygon, Point centroid, double angle)
        {
            for(int i = 0; i < polygon.Length; i++)
            {
                 polygon[i] = rotatePoint(polygon[i], centroid, angle);
            }
 
            return polygon;
        }
 
        public Point rotatePoint(Point point, Point centroid, double angle)
        {
            int x = centroid.X + (int)((point.X - centroid.X) * Math.Cos(angle) - (point.Y - centroid.Y) * Math.Sin(angle));
 
            int y = centroid.Y + (int)((point.X - centroid.X) * Math.Sin(angle) + (point.Y - centroid.Y) * Math.Cos(angle));
 
            return new Point(x, y);
        }

           
         

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Rotate a 2D polygon in C#

Asked by dsmclaughlin in Microsoft Visual C#.Net, Game Programming, Math & Science Questions

Tags: C#, .NET, Visual Studio

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