OpenGL/GLUT Question

**kas2002** · 05-24-2006

I wasn't completely sure where to post this as it's graphics related but not game related and I have posted it in C programming to no avail. I figure I would get a quicker and more likely better response in this forum however.

What I am trying to do is read in points and plot them as spheres (using glut) in 3-D space for a visualization of particles for my physics research. Reading in points and displaying the spheres was no problem (mind you I am new to openGL programming) but I can't seem to set my camera up properly no matter how much I fiddle with it. Heres the case, I am plotting an fcc crystal which is contained in a 6x6x18 box, the bottom left corner of said box being located at the origin. I want to be able to get a good view of this box. I have read various tutorials on camera control in OpenGL and in GLUT and have tried both gluLookAt(); and just translating and rotating; so I am not sure if its just my 3-D math or my understanding of the functions that is off but for some reason I am always zoomed in too far, or can't see anything, the camera never seems to be oriented where I expect. Here is my most recent display function, I was under the assumption that this would locate my camera at (10,10,0) and point it towards the origin.

Code:

void display(void)
{    
     
//****** SET THE SYSTEM UP TO BE A 6X6X18 BOX ********************************//     
     glMatrixMode(GL_PROJECTION);
     glOrtho(0.0,6.0,0.0,6.0,0.0,25.0);

//****** CLEAR BUFFERS **************************************************  *****//     
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    
//****** SETUP THE CAMERA ANGLE*********************************************  **// 
     
     glMatrixMode(GL_PROJECTION);

     glLoadIdentity();
     gluLookAt(0.0,0.0,0.0,10.0,10.0,0.0,0.0,1.0,0.0);

                                           
     glMatrixMode(GL_MODELVIEW); 
                                 
//****** DRAW THE PARTICLES*****************************************  **********//     
    for (int i=0;i<NUM_PARTICLES;i++){DrawParticle(XYZ[i].x,XYZ[i].y,XYZ[i].z);}

    
    glFlush(); 
}

Now I know for a fact everything gets drawn, and drawn correctly because from the various angles I have experimented with (none which give me close to what I want) the crystal structure looks correctly ordered. I was hoping someone could maybe provide a solution or even a good tutorial on camera control which could help me understand how to orient things in openGL. (I have tried nehe.gamedev, along with many others)

Thanks
- J. Paddon

**kas2002** · 05-25-2006

I thought it might help if I posted all the code and attatched the input txt file. I want the crystal to look something like THIS (only mine has different dimensions)

Code:

#include <windows.h>
#include <GL/glut.h>
#include <stdio.h>

//****** DEFINE CONSTANTS AND THE POSITION STRUCTURE *************************//

#define NUM_PARTICLES 2592 

struct Position{
 float x;
 float y;
 float z;
};

//******* GLOBAL VARIABLES ***************************************************//

Position XYZ[NUM_PARTICLES];



//****** DRAWPARTICLE() A SPHERE AT THE POINT USING GLUT *********************//

void DrawParticle(double x, double y, double z){
    glLoadIdentity();
    glPushMatrix();
    glTranslatef(x,y,z);
    glutSolidSphere(0.3,24,24);
    glPopMatrix();    
}


//****** READDATA() OPENS THE COORDINATES FILE AND STORES THEM ***************//

void ReadData() {
   FILE *file;
   file=fopen("001.txt","r");
   
   for(int i=0;i<NUM_PARTICLES;i++){
                      
              fscanf(file," %f %f %f \n", &XYZ[i].x,&XYZ[i].y,&XYZ[i].z);
           
           
   }
      fclose(file);
}

//****** MYINIT() INITALIZES THE OPENGL ENVIROMENT ***************************//

void myInit(void)
{

//****** Initalize Lighting and Turn on Lights for the scene *****************//
    glEnable(GL_LIGHTING);                                                    //                      
    glLightModelf(GL_LIGHT_MODEL_LOCAL_VIEWER,1.0);                           //                       
       GLfloat lightIntensity[]={0.8,0.8,0.8, 0.8};                           //                
       GLfloat lightSpecular[]={1.00,1.0,1.0, 1.0};                           //                
       GLfloat lightPosition[]={0.0,5.00,0.0,1.00};                           //                 
       GLfloat lightAmbient[]={0.50,0.50,0.50,1.0};                           //
                                                                              //
       glLightfv(GL_LIGHT0, GL_DIFFUSE, lightIntensity);                      //
       glLightfv(GL_LIGHT0, GL_SPECULAR, lightSpecular);                      //
       glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);                      //
       glLightfv(GL_LIGHT0, GL_AMBIENT, lightAmbient);                        //
    glEnable(GL_LIGHT0);                                                      //
    glDepthFunc(GL_LEQUAL);                                                   //  
    glEnable(GL_DEPTH_TEST);                                                  //    
}                                                                             //
//****************************************************************************//

//****** ALL THE DRAWING CODE GOES INTO DISP() *******************************//

void display(void)
{    
     
//****** SET THE SYSTEM UP TO BE A 6X6X18 BOX ********************************//     
     glMatrixMode(GL_PROJECTION);
     glOrtho(0.0,6.0,0.0,6.0,0.0,25.0);

//****** CLEAR BUFFERS *******************************************************//     
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    
//****** SETUP THE CAMERA ANGLE***********************************************// 
     
     glMatrixMode(GL_PROJECTION);

     glLoadIdentity();
     gluLookAt(0.0,0.0,0.0,10.0,10.0,0.0,0.0,1.0,0.0);

                                           
     glMatrixMode(GL_MODELVIEW); 
                                 
//****** DRAW THE PARTICLES***************************************************//     
    for (int i=0;i<NUM_PARTICLES;i++){DrawParticle(XYZ[i].x,XYZ[i].y,XYZ[i].z);}

    
    glFlush(); 
}


//****** RESHAPE FUNCTION TO MAINTAIN ASPECT RATIOS **************************// 
//******         WHEN THE WINDOW IS RESIZED         **************************//
//****** FOR THE MOST PART COPY AND PASTED FROM VARIOUS TUTORIALS ************//  
void myReshape(GLsizei w, GLsizei h)                                          //
{                                                                             // 
    glViewport(0, 0, w, h);                                                   //
    glMatrixMode(GL_PROJECTION);                                              //
    glLoadIdentity();                                                         //
    if (w <= h)                                                               //
        glOrtho (-1.5, 1.5, -1.5*(GLfloat)h/(GLfloat)w,                       //
            1.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0);                          //
    else                                                                      //
        glOrtho (-1.5*(GLfloat)w/(GLfloat)h,                                  //
            1.5*(GLfloat)w/(GLfloat)h, -1.5, 1.5, -10.0, 10.0);               //
    glMatrixMode(GL_MODELVIEW);                                               //
    glLoadIdentity();                                                         //
}                                                                             //
//****** END RESIZE FUNCTION**************************************************// 


int main(int argc, char** argv)
{
    ReadData();
    glutInit(&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGBA | GLUT_DEPTH);
    glutInitWindowPosition (10, 10);
    glutInitWindowSize (500,500);
    glutCreateWindow("Visualization Of Crystal Face Structures");
    myInit();
    glutReshapeFunc (myReshape);
    glutDisplayFunc(display2);
    glutMainLoop();
}

**Link_26** · 05-25-2006

So you just want a good view of all the spheres, right?

Well I think your main problem is that glLoadIdentity() function in drawparticle().

By getting rid of that and changing display(void) to:

Code:

void display(void)
{    
     
//****** SET THE SYSTEM UP TO BE A 6X6X18 BOX ********************************//     
     glMatrixMode(GL_PROJECTION);
     glOrtho(0.0,6.0,0.0,6.0,0.0,25.0);

//****** CLEAR BUFFERS **************************************************  *****//     
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    
//****** SETUP THE CAMERA ANGLE*********************************************  **// 
     
     //glMatrixMode(GL_PROJECTION);

  //  glLoadIdentity();
  //  gluLookAt(0.0,0.0,0.0,10.0,10.0,0.0,0.0,1.0,0.0);

                                           
   // glMatrixMode(GL_MODELVIEW); 
                                 
                                 
//****** DRAW THE PARTICLES*****************************************  **********// \
 
   
    for (int i=0;i<NUM_PARTICLES;i++){DrawParticle(XYZ[i].x,XYZ[i].y,XYZ[i].z);}
 
    
    glFlush(); 
}

...I obtained this view:

http://img.villagephotos.com/p/2004-...04/spheres.JPG

Is that kind of what you wanted?

**kas2002** · 05-25-2006

Yes and no, I kinda of want to look at it isometrically like in the picture I linked too in my previous post. I will try adn what you said and see if I can make it work. But if you had any suggestions about how I could orient it so I could see 3 sides at once and have the entire structure within the window that would be amazing.

Thanks
- J. Paddon

**kas2002** · 05-25-2006

I got it, it was due to the glLoadIdentity(); functions I was calling within DrawParticle. Now I was wondering if maybe someone could help me out with a small lighting issue. It would be nice to have this lit up a lot clearer. I have posted a scree shot of the output.

Code:

void myInit(void)
{

//****** Initalize Lighting and Turn on Lights for the scene***************//
    glEnable(GL_LIGHTING);                                                    //                      
    glLightModelf(GL_LIGHT_MODEL_LOCAL_VIEWER,1.0);                           //                       
       GLfloat lightIntensity[]={0.8,0.8,0.8, 0.8};                           //                
       GLfloat lightSpecular[]={1.00,1.0,1.0, 1.0};                           //                
       GLfloat lightPosition[]={0.0,5.00,0.0,1.00};                           //                 
       GLfloat lightAmbient[]={0.50,0.50,0.50,1.0};                           //
                                                                              //
       glLightfv(GL_LIGHT0, GL_DIFFUSE, lightIntensity);                      //
       glLightfv(GL_LIGHT0, GL_SPECULAR, lightSpecular);                      //
       glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);                      //
       glLightfv(GL_LIGHT0, GL_AMBIENT, lightAmbient);                        //
    glEnable(GL_LIGHT0);                                                      //
    glDepthFunc(GL_LEQUAL);                                                   //  
    glEnable(GL_DEPTH_TEST);                                                  //    
}                                                                             //
//*************************************************************************//

**Link_26** · 05-25-2006

Heh I don't know how you got that, but whatever.

Perhaps give the spheres and background a different color...?

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