1 using System;
  2 using Microsoft.DirectX;
  3 using Microsoft.DirectX.Direct3D;
  4
  5 namespace WorldWind
  6 {
  7     /// <summary>
  8     /// The region of space in the modeled world that may appear on the screen; it is the field of view of the notional camera.
  9     /// Used to perform culling of invisible object (prior to rendering) to increase speed.
 10     /// See: http://en.wikipedia.org/wiki/Viewing_frustum
 11     /// </summary>
 12     public class Frustum
 13     {
 14         public Plane[] planes = new Plane[6];
 15
 16         public void Update(Matrix m)
 17         {
 18             //bottom (down) plane
 19             this.planes[0] = new Plane(
 20                 m.M14 + m.M12, //a
 21                 m.M24 + m.M22, //b
 22                 m.M34 + m.M32, //c
 23                 m.M44 + m.M42 //d
 24                 );
 25
 26             //far plane
 27             this.planes[1] = new Plane(
 28                 m.M14 - m.M13,
 29                 m.M24 - m.M23,
 30                 m.M34 - m.M33,
 31                 m.M44 - m.M43
 32                 );
 33
 34             //right side plane
 35             this.planes[2] = new Plane(
 36                 m.M14 - m.M11, //a
 37                 m.M24 - m.M21, //b
 38                 m.M34 - m.M31, //c
 39                 m.M44 - m.M41 //d
 40                 );
 41
 42             //left side plane
 43             this.planes[3] = new Plane(
 44                 m.M14 + m.M11,    //a
 45                 m.M24 + m.M21,    //b
 46                 m.M34 + m.M31,    //c
 47                 m.M44 + m.M41    //d
 48                 );
 49
 50             //near plane
 51             this.planes[4] = new Plane(
 52                 m.M13,
 53                 m.M23,
 54                 m.M33,
 55                 m.M43);
 56
 57             //top (up) plane
 58             this.planes[5] = new Plane(
 59                 m.M14 - m.M12, //a
 60                 m.M24 - m.M22, //b
 61                 m.M34 - m.M32, //c
 62                 m.M44 - m.M42 //d
 63                 );
 64
 65             foreach(Plane p in this.planes)
 66                 p.Normalize();
 67         }
 68
 69         /// <summary>
 70         /// Test if a sphere intersects or is completely inside the frustum.
 71         /// </summary>
 72         /// <returns>true when the sphere intersects.</returns>
 73         public bool Intersects(BoundingSphere c)
 74         {
 75             foreach(Plane p in this.planes)
 76             {
 77                 float distancePlaneToPoint = p.A * c.Center.X + p.B * c.Center.Y + p.C * c.Center.Z + p.D;
 78                 if(distancePlaneToPoint < -c.Radius)
 79                     // More than 1 radius outside the plane = outside
 80                     return false;
 81             }
 82
 83             //else it's in view
 84             return true;
 85         }
 86
 87         /// <summary>
 88         /// Test if a point is inside the frustum.
 89         /// </summary>
 90         /// <returns>true when the point is inside.</returns>
 91         /// <param name="v">XYZ in world coordinates of the point to test.</param>
 92         public bool ContainsPoint(Vector3 v)
 93         {
 94             foreach(Plane p in this.planes)
 95                 if(Vector3.Dot(new Vector3(p.A, p.B, p.C), v) + p.D < 0)
 96                     return false;
 97
 98             return true;
 99         }
100
101         /// <summary>
102         /// Tests if the view frustum fully contains the bounding box.
103         /// </summary>
104         /// <returns>true when the box is complete enclosed by the frustum.</returns>
105         public bool Contains(BoundingBox bb)
106         {
107             //Code taken from Flip Code Article:
108             // http://www.flipcode.com/articles/article_frustumculling.shtml
109             int iTotalIn = 0;
110             foreach(Plane p in this.planes)
111             {
112                 int iInCount = 8;
113                 int iPtIn = 1;
114                 // TODO: Modify bounding box and only check 2 corners.
115                 for(int i = 0; i < 8; i++)
116                 {
117                     if(Vector3.Dot(new Vector3(p.A,p.B,p.C), bb.corners[i]) + p.D < 0)
118                     {
119                         iPtIn = 0;
120                         --iInCount;
121                     }
122                 }
123
124                 if(iInCount == 0)
125                     return false;
126
127                 iTotalIn += iPtIn;
128             }
129
130             if(iTotalIn == 6)
131                 return true;
132
133             return false;
134         }
135
136         /// <summary>
137         /// Tests if the bounding box specified intersects with or is fully contained in the frustum.
138         /// </summary>
139         /// <returns>true when the box intersects with the frustum.</returns>
140         public bool Intersects(BoundingBox bb)
141         {
142             foreach(Plane p in this.planes)
143             {
144                 Vector3 v = new Vector3(p.A,p.B,p.C);
145                 bool isInside = false;
146                 // TODO: Modify bounding box and only check 2 corners.
147                 for(int i = 0; i < 8; i++)
148                 {
149                     if(Vector3.Dot(v, bb.corners[i]) + p.D >= 0)
150                     {
151                         isInside = true;
152                         break;
153                     }
154                 }
155
156                 if(!isInside)
157                     return false;
158             }
159
160             return true;
161         }
162
163         public override string ToString()
164         {
165             string res = string.Format("Near:\n{0}Far:\n{1}", planes[4], planes[1] );
166             return res;
167         }
168     }
169 }