Microsoft.Xna.Framework.Vector2.DistanceSquared C# (CSharp) Method

        public static void DistanceSquared(ref Vector2 value1, ref Vector2 value2, out float result)
        {
            float num = value1.X - value2.X;
            float num2 = value1.Y - value2.Y;
            result = num * num + num2 * num2;
        }
        /// <summary>Calculates the dot product of two vectors. If the two vectors are unit vectors, the dot product returns a floating point value between -1 and 1 that can be used to determine some properties of the angle between two vectors. For example, it can show whether the vectors are orthogonal, parallel, or have an acute or obtuse angle between them.</summary>

        public static bool CollidePolygonAndCircle(
            Fixture fixtureA,
            WorldTransform xfA,
            Fixture fixtureB,
            WorldTransform xfB,
            out Manifold manifold)
        {
            manifold = new Manifold();

            var polygonA = fixtureA as PolygonFixture;
            var circleB  = fixtureB as CircleFixture;

            System.Diagnostics.Debug.Assert(polygonA != null);
            System.Diagnostics.Debug.Assert(circleB != null);

            // Compute circle position in the frame of the polygon.
            var centerInA = xfA.ToLocal(xfB.ToGlobal(circleB.Center));

            var totalRadius  = polygonA.Radius + circleB.Radius;
            var vertexCountA = polygonA.Count;
            var verticesA    = polygonA.Vertices;
            var normalsA     = polygonA.Normals;

            // Find the min separating edge.
            var normalIndexA = 0;
            var separation   = float.MinValue;

            for (var i = 0; i < vertexCountA; ++i)
            {
                var s = Vector2Util.Dot(normalsA[i], centerInA - verticesA[i]);

                if (s > totalRadius)
                {
                    // Early out.
                    manifold = new Manifold();
                    return(false);
                }

                if (s > separation)
                {
                    separation   = s;
                    normalIndexA = i;
                }
            }

            // Vertices that subtend the incident face.
            var vertexIndexA1 = normalIndexA;
            var vertexIndexA2 = vertexIndexA1 + 1 < vertexCountA ? vertexIndexA1 + 1 : 0;
            var vertexA1      = verticesA[vertexIndexA1];
            var vertexA2      = verticesA[vertexIndexA2];

            // If the center is inside the polygon ...
            if (separation < Settings.Epsilon)
            {
                manifold.Type       = Manifold.ManifoldType.FaceA;
                manifold.PointCount = 1;
                manifold.Points.Item1.LocalPoint = circleB.Center;
                manifold.Points.Item1.Id.Key     = 0;

                manifold.LocalNormal = normalsA[normalIndexA];
                manifold.LocalPoint  = 0.5f * (vertexA1 + vertexA2);
                return(true);
            }

            // Compute barycentric coordinates
            var u1 = Vector2Util.Dot(centerInA - vertexA1, vertexA2 - vertexA1);
            var u2 = Vector2Util.Dot(centerInA - vertexA2, vertexA1 - vertexA2);

            if (u1 <= 0.0f)
            {
                if (LocalPoint.DistanceSquared(centerInA, vertexA1) <= totalRadius * totalRadius)
                {
                    var normalInA = centerInA - vertexA1;
                    normalInA.Normalize();

                    manifold.Type       = Manifold.ManifoldType.FaceA;
                    manifold.PointCount = 1;
                    manifold.Points.Item1.LocalPoint = circleB.Center;
                    manifold.Points.Item1.Id.Key     = 0;

                    manifold.LocalNormal = normalInA;
                    manifold.LocalPoint  = vertexA1;
                    return(true);
                }
            }
            else if (u2 <= 0.0f)
            {
                if (LocalPoint.DistanceSquared(centerInA, vertexA2) <= totalRadius * totalRadius)
                {
                    manifold.Type       = Manifold.ManifoldType.FaceA;
                    manifold.PointCount = 1;
                    manifold.Points.Item1.LocalPoint = circleB.Center;
                    manifold.Points.Item1.Id.Key     = 0;

                    manifold.LocalNormal = centerInA - vertexA2;
                    manifold.LocalNormal.Normalize();
                    manifold.LocalPoint = vertexA2;
                    return(true);
                }
            }
            else
            {
                var faceCenter = 0.5f * (vertexA1 + vertexA2);
                if (Vector2Util.Dot(centerInA - faceCenter, normalsA[vertexIndexA1]) <= totalRadius)
                {
                    manifold.Type       = Manifold.ManifoldType.FaceA;
                    manifold.PointCount = 1;
                    manifold.Points.Item1.LocalPoint = circleB.Center;
                    manifold.Points.Item1.Id.Key     = 0;

                    manifold.LocalNormal = normalsA[vertexIndexA1];
                    manifold.LocalPoint  = faceCenter;
                    return(true);
                }
            }

            return(false);
        }