java3D中平行光投影的实现 - 王朝网络宽屏版

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非凡，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.COORDINATESGeometryArray.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));