影行列をJOGLでやってみた

動機
これに影とかつけたいなー．
OpenGLでどうやるんだろうー．影行列っていうのをつかうみたいだなー．
解説とサンプルが載ってる．
JOGLでやってみよう！．

感謝
解説，サンプル掲載ありがとうございます！

やってみた
JOGLの環境については以前のモノ等を参照してください．

上記サイトのサンプルの設定

光源位置(7, 5, 5)、平面の方程式　y + 1 = 0とした時に、
物体を描画し、平面「y + 1 = 0」に影を描画せよ。

これをJOGLでやってみたい．

ただここでは描画対象を球に変更し，光源を高さ(y)5の平面上の半径8の円周上でグルグル回しています．
tの上限とか見てないぐらい'てきとー'．

コード

import java.awt.Frame;
import java.awt.Insets;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.nio.FloatBuffer;
import javax.media.opengl.GL;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GLCanvas;
import javax.media.opengl.GLEventListener;
import javax.media.opengl.glu.GLU;
import javax.media.opengl.glu.GLUquadric;
import com.sun.opengl.util.FPSAnimator;

public class Sample implements GLEventListener {

 private final static int SCREEN_X = 640;
 private final static int SCREEN_Y = 480;
 float ShadowMatrix_ary[] = new float[16];
 float plane_ary[] = { 0.0f, 1.0f, 0.0f, 1.0f };
 float light_pos_ary[] = { 8.0f, 5.0f, 0.0f, 1.0f };
 FloatBuffer light_pos = FloatBuffer.wrap(light_pos_ary);
 float OffsetFactor = 1.0f;
 float OffsetUnit = 0.0f;
 float floorcolor_ary[] = { 0.8f, 0.8f, 0.8f, 1.0f };
 FloatBuffer floorcolor = FloatBuffer.wrap(floorcolor_ary);
 float red_ary[] = { 0.8f, 0.2f, 0.2f, 1.0f };
 FloatBuffer red = FloatBuffer.wrap(red_ary);
 private FPSAnimator animator;
 private double t;
 
 public Sample() {
  Frame frame = new Frame("Sample JOGL");
  frame.setVisible(true);
  Insets ins = frame.getInsets();
  frame.setSize(SCREEN_X + ins.left + ins.right, SCREEN_Y + ins.top
    + ins.bottom);
  frame.addWindowListener(new WindowAdapter() {
   public void windowClosing(WindowEvent e) {
    System.exit(0);
   }
  });
  GLCanvas canvas = new GLCanvas();
  frame.add(canvas);
  canvas.addGLEventListener(this);
  canvas.setBounds(ins.left, ins.top, SCREEN_X, SCREEN_Y);
 }
 
 public void init(GLAutoDrawable drawable) {
  GL gl = drawable.getGL();
  gl.glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
  {
   gl.glEnable(GL.GL_LIGHTING);
   gl.glEnable(GL.GL_LIGHT0);
   gl.glLightfv(GL.GL_LIGHT0, GL.GL_POSITION, light_pos);
   gl.glEnable(GL.GL_DEPTH_TEST);
  }
  CalcShadowMatrixf(plane_ary, light_pos_ary, ShadowMatrix_ary);
  animator = new FPSAnimator(drawable, 60);
  animator.start();
  t = 0.0f;
 }
 
 public void reshape(GLAutoDrawable drawable, int x, int y, int w, int h) {
  GL gl = drawable.getGL();
  GLU glu = new GLU();
  gl.glViewport(0, 0, w, h);
  gl.glMatrixMode(GL.GL_PROJECTION);
  gl.glLoadIdentity();
  glu.gluPerspective(30.0, (double) w / (double) h, 1.0, 100.0);
  gl.glMatrixMode(GL.GL_MODELVIEW);
 }
 
 public void display(GLAutoDrawable drawable) {
  GL gl = drawable.getGL();
  GLU glu = new GLU();
  light_pos_ary[0] = Double.valueOf(9.0 * Math.cos(t)).floatValue();
  light_pos_ary[2] = Double.valueOf(9.0 * Math.sin(t)).floatValue();
  t+= 0.01;
  CalcShadowMatrixf(plane_ary, light_pos_ary, ShadowMatrix_ary);
  
  gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);
  gl.glLoadIdentity();
  glu.gluLookAt(6.0, 7.0, 8.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
  float xAngle = 0f;
  float yAngle = 0f;
  gl.glRotated(xAngle, 1, 0, 0);
  gl.glRotated(yAngle, 0, 1, 0);
  gl.glLightfv(GL.GL_LIGHT0, GL.GL_POSITION, light_pos);
  {
   // 床を描画
   gl.glEnable(GL.GL_POLYGON_OFFSET_FILL);
   gl.glPushMatrix();
   gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL.GL_DIFFUSE, floorcolor);
   gl.glPolygonOffset(OffsetFactor, OffsetUnit);
   if (true) {
    gl.glTranslatef(0, -1, 0);
    gl.glRotatef(90, -1, 0, 0);
    gl.glNormal3d(0, 0, 1);
    gl.glRectf(-5, 5, 5, -5);
   }
   gl.glPopMatrix();
   gl.glDisable(GL.GL_POLYGON_OFFSET_FILL);
  }
  {
   // 通常の描画
   gl.glPushMatrix();
   gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL.GL_DIFFUSE, red);
   if (true) {
    GLUquadric qobj0 = glu.gluNewQuadric();
    glu.gluQuadricDrawStyle(qobj0, GLU.GLU_FILL);
    glu.gluQuadricNormals(qobj0, GLU.GLU_SMOOTH);
    glu.gluSphere(qobj0, 0.8f, 20, 20);
    // glutSolidTeapot(1);
   }
   gl.glPopMatrix();
  }
  {
   // 影の描画
   gl.glDisable(GL.GL_LIGHTING);
   gl.glDisable(GL.GL_LIGHT0);
   gl.glPushMatrix();
   gl.glMultMatrixf(ShadowMatrix_ary, 0);
   gl.glColor3d(0, 0, 0);
   if (true) {
    GLUquadric qobj0 = glu.gluNewQuadric();
    glu.gluQuadricDrawStyle(qobj0, GLU.GLU_FILL);
    glu.gluQuadricNormals(qobj0, GLU.GLU_SMOOTH);
    glu.gluSphere(qobj0, 0.8f, 20, 20);
    // glutSolidTeapot(1);
   }
   gl.glPopMatrix();
   gl.glEnable(GL.GL_LIGHTING);
   gl.glEnable(GL.GL_LIGHT0);
  }
 }
 
 void CalcShadowMatrixf(float[] planeAry, float[] lightPosAry,
   float[] shadowMatrixAry) {
  float dot = 0.0f;
  for (int i = 0; i < 4; i++) {
   dot += planeAry[i] * lightPosAry[i];
  }
  for (int loopY = 0; loopY < 4; ++loopY) {
   for (int loopX = 0; loopX < 4; ++loopX) {
    shadowMatrixAry[loopY * 4 + loopX] = -planeAry[loopY]
      * lightPosAry[loopX];
    if (loopX == loopY) {
     shadowMatrixAry[loopY * 4 + loopX] += dot;
    }
   }
  }
 }
 
 @Override
 public void displayChanged(GLAutoDrawable arg0, boolean arg1, boolean arg2) {
  //
 }
 
 public static void main(String[] args) {
  new Sample();
 }
}

結果