I am trying to do a surface-of-revolution and display the object as a wireframe representation, rotating around and saving the points


It has no compile errors, but it has a runtime error in the black screen saying:

java.lang.NullPointerException
       at Rotation6$Renderer.display(Rotation6.java:205)
       at net.java.games.jogl.impl.GLDrawableHelper.display(GLDrawableHelper.ja
va:74)
       at net.java.games.jogl.GLCanvas$DisplayAction.run(GLCanvas.java:194)
       at net.java.games.jogl.impl.GLContext.invokeGL(GLContext.java:192)
       at net.java.games.jogl.GLCanvas.displayImpl(GLCanvas.java:182)
       at net.java.games.jogl.GLCanvas.display(GLCanvas.java:82)
       at net.java.games.jogl.Animator$1.run(Animator.java:104)
       at java.lang.Thread.run(Thread.java:536)

how do I fix this problem?

-----------------------------------------------------------------------

here is the code




import java.awt.*;
import java.awt.event.*;
import java.nio.IntBuffer;
import net.java.games.jogl.*;
import net.java.games.jogl.util.*;



public class Rotation6

{


static Animator animator = null;



public static void main(String[] args)

{

Frame frame = new Frame("Rotation ");

GLCanvas canvas = GLDrawableFactory.getFactory().createGLCanvas(new GLCapabilities());

canvas.addGLEventListener(new Renderer());

frame.add(canvas);

frame.setSize(500, 500);

animator = new Animator(canvas);

frame.addWindowListener(new WindowAdapter()

{

public void windowClosing(WindowEvent e)

{

animator.stop();

System.exit(0);

}

});

frame.show();

animator.start();

canvas.requestFocus();



} // end main



static class Renderer implements GLEventListener, KeyListener {
 
 private float rtri = 0.0f;
 



public class wcPt3D {

     public float x, y, z;

     

     wcPt3D(float xcoord, float ycoord, float zcoord){

           x= xcoord;

           y= ycoord;
             
           z= zcoord;

    }

   

    wcPt3D( ){

    x = 0.0f;

    y = 0.0f;
   
    z = 0.0f;

     }
     
     

} // end wcpt3d



public void init(GLDrawable gLDrawable)

{

final GL gl = gLDrawable.getGL();

final GLU glu = gLDrawable.getGLU();



gl.glMatrixMode (GL.GL_PROJECTION);

gl.glClearColor (1.0f, 0.0f, 0.0f, 0.0f); //set background to white

gl.glClearDepth(1.0f); // Depth Buffer Setup

gl.glEnable(GL.GL_DEPTH_TEST); // Enables Depth Testing

gl.glDepthFunc(GL.GL_LEQUAL); // The Type Of Depth Testing To Do

gl.glOrtho (-2.0, 2.0, -2.0, 2.0, -15.0, 15.0); // define drawing area
gl.glClearColor (0.0f, 0.0f, 0.0f, 0.0f);

gLDrawable.addKeyListener(this);

}







public void keyReleased(KeyEvent e) {}



public void keyTyped(KeyEvent e) {}




public void display(GLDrawable gLDrawable)

{

final GL gl = gLDrawable.getGL();

final GLU glu = gLDrawable.getGLU();



gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT); // Set display window to color.

gl.glMatrixMode (GL.GL_MODELVIEW);



gl.glLoadIdentity();

gl.glRotatef(rtri, 0.0f, 2.0f, 0.0f);


gl.glBegin(GL.GL_LINES); //drawing using lines

wcPt3D[][] p1 = new wcPt3D[10][36];

float angle=0.0f;

     int i =0;
     

p1[0][0] =new wcPt3D (0.150f, 0.750f, 0.000f);
p1[1][0] =new wcPt3D (0.450f, 0.750f, 0.000f);
p1[2][0] =new wcPt3D (0.450f, 0.750f, 0.000f);
p1[3][0] =new wcPt3D (0.650f, 0.500f, 0.000f);
p1[4][0] =new wcPt3D (0.650f, 0.500f, 0.000f);
p1[5][0] =new wcPt3D (0.350f, 0.350f, 0.000f);
p1[6][0] =new wcPt3D (0.350f, 0.350f, 0.000f);
p1[7][0] =new wcPt3D (0.150f, 0.350f, 0.000f);
p1[8][0] =new wcPt3D (0.150f, 0.350f, 0.000f);
p1[9][0] =new wcPt3D (0.150f, 0.150f, 0.000f);

for (int row = 0; row < 36; row++) {
     gl.glBegin(GL.GL_LINES);
        
        for (int col = 0; col < 10; col++) {
           gl.glVertex3f(p1[row][col].x, p1[row][col].y, p1[row][col].z);



     }
gl.glEnd();
}



/*gl.glVertex3f(0.150f, 0.750f, 0.000f);
gl.glVertex3f(0.450f, 0.750f, 0.000f);
gl.glVertex3f(0.450f, 0.750f, 0.000f);
gl.glVertex3f(0.650f, 0.500f, 0.000f);
gl.glVertex3f(0.650f, 0.500f, 0.000f);
gl.glVertex3f(0.350f, 0.350f, 0.000f);
gl.glVertex3f(0.350f, 0.350f, 0.000f);
gl.glVertex3f(0.150f, 0.350f, 0.000f);
gl.glVertex3f(0.150f, 0.350f, 0.000f);
gl.glVertex3f(0.150f, 0.150f, 0.000f);
*/









gl.glEnd(); // Finished

rtri += 0.2f;

//}
gl.glFlush();
}

public void displayChanged(GLDrawable gLDrawable, boolean modeChanged, boolean deviceChanged)

{

}



public void reshape(GLDrawable gLDrawable, int x, int y, int width, int height)

{



}
public void keyPressed(KeyEvent e)

{

if (e.getKeyCode() == KeyEvent.VK_ESCAPE)

animator.stop();

System.exit(0);

}

   




public void rotate3D (wcPt3D[][] p1)

{



float deg = 0;
float RadianAngle = (float)(180/Math.PI);
 
     for (int row = 0; row < 36; row++) {
     

     for (int col = 0; col < 10; col++) {
     
   float zp = p1[row][col].z * (float)Math.cos(deg * RadianAngle) - p1[row][col].x * (float)Math.sin(deg * RadianAngle);
   float xp = p1[row][col].z * (float)Math.sin(deg * RadianAngle) + p1[row][col].x * (float)Math.cos(deg * RadianAngle);
   float yp = p1[row][col].y;
     
 p1[row][col] = new wcPt3D(xp, yp, zp);

 
  deg += 10.0f;
 
   }
   
     }
          
    }
     
public void draw3D (wcPt3D[][] p1, GL gl)

{


for (int row = 0; row < 36; row++) {
     gl.glBegin(GL.GL_LINES);
        
        for (int col = 0; col < 10; col++) {
           gl.glVertex3f(p1[row][col].x, p1[row][col].y, p1[row][col].z);
   


     }
gl.glEnd();
}


}







}

}

I have made some changes to the program and called the BarChart2 and winReshapeFcn inside the display. It compiles ok and has no errors, but I still get that blank black screen at execution(BarChart screen) and no display of the barchart.

import java.awt.*;
import java.awt.event.*;
import net.java.games.jogl.*;
import net.java.games.jogl.util.*;

public class BarChart2 {



public static void main(String[] args)

 {
 
   
   Frame frame = new Frame("Bar Chart");

   GLCanvas canvas = GLDrawableFactory.getFactory().createGLCanvas(new GLCapabilities());

   canvas.addGLEventListener(new Renderer());
 
   frame.add(canvas);

   frame.setSize(500, 600);

frame.addWindowListener(new WindowAdapter()

   {

     public void windowClosing(WindowEvent e)

     {

       

       System.exit(0);

     }

   });

   frame.show();
 
   canvas.requestFocus();
}

static class Renderer implements GLEventListener, KeyListener

 {
       

   


public void init(GLDrawable gLDrawable)

   {
final GL gl = gLDrawable.getGL();
final GLU glu = gLDrawable.getGLU();
gl.glColor3f (0.0f, 0.0f, 0.75f);  
gl.glMatrixMode (GL.GL_PROJECTION);  
gl.glLoadIdentity();

     

     //lineSegment(gLDrawable.getGL());
}
 


   
public void display(GLDrawable gLDrawable)//, int winWidth, int winHeight)


   {

    final GL gl = gLDrawable.getGL();
    final GLU glu = gLDrawable.getGLU();
    final GLUT glut = new GLUT();
   

   

   
     gl.glClear (GL.GL_COLOR_BUFFER_BIT);// Set display to color.

     gl.glColor3f (0.0f, 0.0f, 0.75f);  

             
     winReshapeFcn (gl, glu);//, gluOrtho2D, glClear); //, //GL_COLOR_BUFFER_BIT);    

     BarChart2(gl, glut);
     gl.glMatrixMode (GL.GL_MODELVIEW);

     gl.glLoadIdentity();



int winWidth = 600;
int winHeight = 500; //Initial display window size
int xRaster = 25;
int yRaster = 150;
/*gl.GLubyte*/ char[] label /*[36]*/  = { 'J','a','n', 'F','e','b', 'M','a','r',
                      'A','p','r', 'M','a','y', 'J','u','n',
                      'J','u','l', 'A','u','g', 'S','e','p',
                      'O','c','t', 'N','o','v', 'D','e','c' };


int[] dataValue /*[12]*/  = {420, 342, 324, 310, 262, 185,
                       190, 196, 217, 240, 312, 438 };
   
gl.glClearColor (1.0f, 1.0f, 0.0f, 0.0f); //White display window
gl.glMatrixMode (GL.GL_PROJECTION);                    
 }

 

public void displayChanged(GLDrawable gLDrawable, boolean modeChanged, boolean deviceChanged)

   {

   }

  public void reshape(GLDrawable gLDrawable, int x, int y, int width, int height)

   {

     

   }



   


public void BarChart2 (GL gl, GLUT glut)//, int xRaster, int yRaster, int[] dataValue)//,  //char[] label, char h)
{

     int xRaster;
     int yRaster;
     int month;
//      int[] dataValue;
     char[] label;
     int k;
     char h;

 int[] dataValue  = {420, 342, 324, 310, 262, 185,
                       190, 196, 217, 240, 312, 438 };
     
     //gl.glClear (GL.GL_COLOR_BUFFER_BIT); //Clear display window
     
     gl.glColor3f (1.0f, 1.0f,0.0f); // Set bar color to red
     for (k = 0; k < 12; k++)
     
     gl.glRecti (20 + k*50, 165, 40 + k*50, dataValue [k]);
     
//      gl.glColor4f (1.0f, 1.0f, 1.0f, 1.0f); // Set test color to black
     xRaster = 25; //20;              // Display chart labels
     yRaster = 150;
     for (month = 0; month < 12; month++) {
           gl.glRasterPos2i (xRaster, yRaster);
           for (k = 3*month; k <3 * month + 3; k++)
     //glut.glutBitmapCharacter(GLUT.BITMAP_HELVETICA_12, label [h]);       //glut.glutBitmapCharacter  //(GLUT.BITMAP_HELVETICA_12,//label[h]);
           xRaster +=50;


     }
gl.glFlush ();      
}
     

     

public void winReshapeFcn (GL gl, GLU glu)//, GLU gluOrtho2D, GL glClear)//, GL GL_COLOR_BUFFER_BIT)    
{
     
     double newWidth =0.0;
     double newHeight= 0.0;
     GL GL_COLOR_BUFFER_BIT;
     GLU gluOrtho2D;
     GL glClear;
     gl.glMatrixMode (GL.GL_PROJECTION);
     gl.glLoadIdentity ();
     glu.gluOrtho2D (0.0, (double) newWidth, 0.0, (double) newHeight);
     gl.glClear (GL.GL_COLOR_BUFFER_BIT);

     

     }




   

   public void keyPressed(KeyEvent e)

   {

     if (e.getKeyCode() == KeyEvent.VK_ESCAPE)

       System.exit(0);

   }
   

   public void keyReleased(KeyEvent e) {}

   

   public void keyTyped(KeyEvent e) {}

     

 

 }


}

whenever I try anything.BarChart2() I get a cannot resolve symbol error

Whenever I run this, it compiles, but I get a black screen, what can I do to get the barchart to show up?


import java.awt.*;
import java.awt.event.*;
import net.java.games.jogl.*;
import net.java.games.jogl.util.*;

public class BarChart2 {


public static void main(String[] args)

 {

   Frame frame = new Frame("Bar Chart");

   GLCanvas canvas = GLDrawableFactory.getFactory().createGLCanvas(new GLCapabilities());

   canvas.addGLEventListener(new Renderer());
   //frame.display();
   frame.add(canvas);

   frame.setSize(500, 600);



     

   frame.addWindowListener(new WindowAdapter()

   {

     public void windowClosing(WindowEvent e)

     {

       

       System.exit(0);

     }

   });

   frame.show();

   canvas.requestFocus();
}
static class Renderer implements GLEventListener, KeyListener

 {
       



     


public void init(GLDrawable gLDrawable)

   {
final GL gl = gLDrawable.getGL();
final GLU glu = gLDrawable.getGLU();
gl.glColor3f (0.0f, 0.0f, 0.75f);  
gl.glMatrixMode (GL.GL_PROJECTION);  
gl.glLoadIdentity();

     

     //lineSegment(gLDrawable.getGL());

   

   }


   
public void display(GLDrawable gLDrawable)//, int winWidth, int winHeight)


   {

    final GL gl = gLDrawable.getGL();
    final GLU glu = gLDrawable.getGLU();
 
   
     gl.glClear (GL.GL_COLOR_BUFFER_BIT);// Set display to color.

           //gl.glColor3f (0.0f, 0.0f, 0.75f);  

             

     gl.glMatrixMode (GL.GL_MODELVIEW);

     gl.glLoadIdentity();



int winWidth = 600;
int winHeight = 500; //Initial display window size
//setSize (600,500);
//gl.GLint xRaster = 25;
//gl.GLint yRaster = 150; //Initialize raster position
int xRaster = 25;
int yRaster = 150;
/*gl.GLubyte*/ char[] label /*[36]*/  = { 'J','a','n', 'F','e','b', 'M','a','r',
                      'A','p','r', 'M','a','y', 'J','u','n',
                      'J','u','l', 'A','u','g', 'S','e','p',
                      'O','c','t', 'N','o','v', 'D','e','c' };


int[] dataValue /*[12]*/  = {420, 342, 324, 310, 262, 185,
                       190, 196, 217, 240, 312, 438 };
   
gl.glClearColor (1.0f, 1.0f, 0.0f, 0.0f); //White display window
gl.glMatrixMode (GL.GL_PROJECTION);                    
 }

 

public void displayChanged(GLDrawable gLDrawable, boolean modeChanged, boolean deviceChanged)

   {

   }

  public void reshape(GLDrawable gLDrawable, int x, int y, int width, int height)

   {

     

   }



   







public void BarChart2 (GL gl, GLUT glut, int xRaster, int yRaster, int[] dataValue,  char[] label, char h)
{
//      char[] label;
     int month;
     int k;
//      char h;
     gl.glClear (GL.GL_COLOR_BUFFER_BIT); //Clear display window
     
     gl.glColor3f (1.0f, 1.0f,0.0f); // Set bar color to red
     for (k = 0; k < 12; k++)
     
     gl.glRecti (20 + k*50, 165, 40 + k*50, dataValue [k]);
     
//      gl.glColor4f (1.0f, 1.0f, 1.0f, 1.0f); // Set test color to black
     xRaster = 20;              // Display chart labels
     for (month = 0; month < 12; month++) {
           gl.glRasterPos2i (xRaster, yRaster);
           for (k = 3*month; k <3 * month + 3; k++)
     //glut.glutBitmapCharacter(GLUT.BITMAP_HELVETICA_12, label [h]);       //glut.glutBitmapCharacter  //(GLUT.BITMAP_HELVETICA_12,//label[h]);
           xRaster +=50;
     
     
     }
gl.glFlush ();      

}      

public void winReshapeFcn (GL gl, GLU glu, int newWidth, int newHeight, GLU gluOrtho2D, GL glClear, GL GL_COLOR_BUFFER_BIT)    
{
     gl.glMatrixMode (GL.GL_PROJECTION);
     gl.glLoadIdentity ();
     glu.gluOrtho2D (0.0, (double) newWidth, 0.0, (double) newHeight);
     gl.glClear (GL.GL_COLOR_BUFFER_BIT);

     

     }



   

   public void keyPressed(KeyEvent e)

   {

     if (e.getKeyCode() == KeyEvent.VK_ESCAPE)

       System.exit(0);

   }
   

   public void keyReleased(KeyEvent e) {}

   

   public void keyTyped(KeyEvent e) {}

 }


}