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java3D中平行光投影的实现

理论根据:假设一个光的方向是(-1,-1,-1) , 投影到XZ平面

一个是直线方程,一个是平面方程,求交而且平面方程还比较特殊,经过原点,法向量是 0 1 0简化后就简单了, 假定v是直线的方向

  x – vertex.x       y – vertex.y        z-vertex.z—————-  = ————— = ————–         直线方程     v.x               v.y                 v.z

平面方程 y = 0

带入就得到了x = vertex.x + v.x / v.y * (-vertex.y)z = vertex.z + v.x / v.z * (-vertex.z)

源程序:import java.applet.Applet;import java.awt.BorderLayout;import java.awt.GraphicsConfiguration;import java.awt.Label;import com.sun.j3d.utils.applet.MainFrame;import com.sun.j3d.utils.universe.*;import com.sun.j3d.utils.geometry.*;import javax.media.j3d.*;import javax.vecmath.*;public class SimpleShadow extends Applet{ //三角平面类 public class TriPlane extends Shape3D{  TriPlane(Point3f A,Point3f B,Point3f C){   this.setGeometry(this.createGeometry3(A,B,C));   this.setAppearance(this.createAppearance());  }  //建立三角平面    Geometry createGeometry3(Point3f A,Point3f B,Point3f C){   TriangleArray plane=new TriangleArray(3,GeometryArray.COORDINATES|GeometryArray.NORMALS);   //设置平面3个顶点的坐标   plane.setCoordinate(0,A);   plane.setCoordinate(1,B);   plane.setCoordinate(2,C);      //计算平面法向量   Vector3f a=new Vector3f(A.x-B.x,A.y-B.y,A.z-B.z);   Vector3f b=new Vector3f(C.x-B.x,C.y-B.y,C.z-B.z);   Vector3f n=new Vector3f();   n.cross(b,a);   //法向量单位化   n.normalize();   //设置平面3个顶点的法向量   plane.setNormal(0,n);   plane.setNormal(1,n);      plane.setNormal(2,n);   return plane;  }    //创建Material不为空的外观    Appearance createAppearance(){   Appearance appear=new Appearance();   Material material=new Material();   appear.setMaterial(material);   return appear;  }   }   //四边平面类 public class QuadPlane extends Shape3D{    QuadPlane(Point3f A,Point3f B,Point3f C,Point3f D){   this.setGeometry(this.createGeometry4(A,B,C,D));   this.setAppearance(this.createAppearance());  }    //创建四边性平面  Geometry createGeometry4(Point3f A,Point3f B,Point3f C,Point3f D){   QuadArray plane=new QuadArray(4,GeometryArray.COORDINATES|GeometryArray.NORMALS);   //设置平面3个顶点的坐标   plane.setCoordinate(0,A);   plane.setCoordinate(1,B);   plane.setCoordinate(2,C);   plane.setCoordinate(3,D);   //计算平面法向量   Vector3f a=new Vector3f(A.x-B.x,A.y-B.y,A.z-B.z);   Vector3f b=new Vector3f(C.x-B.x,C.y-B.y,C.z-B.z);   Vector3f n=new Vector3f();   n.cross(b,a);   //法向量单位化   n.normalize();   //设置平面4个顶点的法向量   plane.setNormal(0,n);   plane.setNormal(1,n);   plane.setNormal(2,n);   plane.setNormal(3,n);   return plane;  }  

//创建Material不为空的外观    Appearance createAppearance(){   Appearance appear=new Appearance();   Material material=new Material();   appear.setMaterial(material);   return appear;  } }   //阴影类 public class Shadow3D extends Shape3D{  Shadow3D(GeometryArray geom,Vector3f direction,Color3f col,float height){   int vCount=geom.getVertexCount();   TriangleArray poly=new TriangleArray(vCount,GeometryArray.COORDINATES|GeometryArray.COLOR_3);   int v;   Point3f vertex=new Point3f();   Point3f shadow=new Point3f();      for(v=0;v<vCount;v++){    //计算可见面顶点在投影面上的投影坐标    geom.getCoordinate(v,vertex);    System.out.println(vertex.y-height);          shadow.set(vertex.x-(vertex.y-height),height+0.0001f,vertex.z-(vertex.y-height));          poly.setCoordinate(v,shadow);          poly.setColor(v,col);

   }   this.setGeometry(poly);     } }   public SimpleShadow(){  this.setLayout(new BorderLayout());   //GraphicsConfiguration config =SimpleUniverse.getPreferredConfiguration();  Canvas3D c=new Canvas3D(null);  this.add("Center",c);  //创建分支节点  BranchGroup scene=new BranchGroup();  //创建三角形可见平面  Shape3D plane=new TriPlane(new Point3f(0.0f,0.6f,-0.2f),new Point3f(-0.3f,-0.3f,0.2f),new Point3f(0.6f,-0.3f,0.2f));  //添加到根分支节点  scene.addChild(plane);  //创建四边形投影平面  Shape3D floor=new QuadPlane(new Point3f(-1.0f,-0.5f,-1.0f),new Point3f(-1.0f,-0.5f,1.0f),new Point3f(1.0f,-0.5f,1.0f),new Point3f(1.0f,-0.5f,-1.0f));  //添加到根分支节点  scene.addChild(floor);  //添加到环境光  AmbientLight lightA=new AmbientLight();  lightA.setInfluencingBounds(new BoundingSphere());  scene.addChild(lightA);  //添加平行光  DirectionalLight lightD1=new DirectionalLight();  lightD1.setInfluencingBounds(new BoundingSphere());  Vector3f direction=new Vector3f(-1.0f,-1.0f,-1.0f);  //方向矢量单位化   direction.normalize();  lightD1.setDirection(direction);  scene.addChild(lightD1);  //创建阴影物体  Shape3D shadow=new Shadow3D((GeometryArray)plane.getGeometry(),direction,new Color3f(0.2f,0.2f,0.2f),-0.5f);  scene.addChild(shadow);  SimpleUniverse u=new SimpleUniverse(c);  u.getViewingPlatform().setNominalViewingTransform();  u.addBranchGraph(scene); }  public static void main(String argv[]){  new MainFrame(new SimpleShadow(),256,256); }

}

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