new to OpenGL: glutMouseFunc

Question

I'm trying to change the sphere position after a mouse click but it doesnt work when using the x and y from glutMouseFunc ,, here is the code :

//

   #include "stdafx.h"
    #include <stdlib.h>
    #include <GL/glut.h>


    bool Cone=false , ConeSelected=false,
    Cube=false, CubeSelected=false,
    Sphere=false, SphereSelected=false,
    Teapot=false, TeapotSelected =false,
    Torus=false, TorusSelected=false;
    static float XSphere=0, YSphere=-1.5 ,ZSphere=0;

    void init(void) 
    {
    GLfloat blankMaterial[] = {1.0, 0.0, 0.0};
    GLfloat whiteDiffuseLight[] = {30}; 
    glClearColor (0.0, 0.1, 0.2, 0.0);
    glClearDepth(1.0);
    glShadeModel (GL_FLAT);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_DEPTH_TEST);
    glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, blankMaterial);
    glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, blankMaterial);
    glMaterialfv(GL_FRONT_AND_BACK, GL_SHININESS,  whiteDiffuseLight);
     }


    void display(void)
    {
      glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
      glEnable(GL_DEPTH_TEST);

      //Drawing Cube
       if(Cube)
        {
        glPushMatrix();
        glColor3f(0, 1, 0);
        glTranslatef(-3,0,-3);
        glRotatef(20, 1,0,0);
        glutSolidCube(2);
        glPopMatrix() ;
        }

      //drawing cone
       if(Cone)
      {
        glPushMatrix();
        glColor3f (1.0, 0.0, 1.0);
        glTranslatef(0,2,0);
        glRotatef(50, 1,0,0);
        glutSolidCone(.5,1,10,10);
        glPopMatrix() ;
       }

      //Drawing Solid Sphere
      if(Sphere)
      { 
       glPushMatrix();
       glTranslatef(XSphere,YSphere,ZSphere);
       glutSolidSphere(.5, 20, 20);
       glPopMatrix();
       glDisable(GL_DEPTH_TEST);
   }
   glColor3f (1.0f, 1.0f, 1.0f);

   //drawing Torus
   if(Torus)
   {
        glPushMatrix();
        glColor3f (1.0, 1.0, 1.0);
        glTranslatef(2,2,0);
        glRotatef(60, 1,0,0);
        glutSolidTorus(.2,.5,40,30);
        glPopMatrix() ;
   }

   //Drawing teapot
   if(Teapot)
   {
       glPushMatrix ();
       glTranslatef (2.0, 0.0, 0.0);
       glutSolidTeapot(.5);
       glPopMatrix ();
   }


glFlush();
glutSwapBuffers();



}

void reshape (int w, int h)
{
   glViewport (0, 0, (GLsizei) w, (GLsizei) h); 
   glMatrixMode (GL_PROJECTION);
   glLoadIdentity ();
   gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0);

   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
   gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
}

void keyboard (unsigned char key, int x, int y)
{int modifiers = glutGetModifiers();

   switch (key) {
       case 'A':
               Teapot=Cone=Sphere=Cube=Torus=true;
               glutPostRedisplay();
               break;
        case 'D':
               Teapot=Cone=Sphere=Cube=Torus=false;
               glutPostRedisplay();
               break;
        case 'S':
                Teapot=Cone=Cube=Torus=false;
                Sphere=true;
                TeapotSelected=ConeSelected=CubeSelected=TorusSelected=false;
                SphereSelected=true;

               break;       
      case 27:
         exit(0);
         break;
      default:
         break;
   }
}

Here in the mouse section I tried to set the gltranslation in the above drawing sphere but when I checked the results for x and y they were large and that's why I couldnt see the sphere after clicking the mouse , how can i fix this ??

void MyMouse(int button, int state, int x, int y)
{

switch (button)
{
    case GLUT_LEFT_BUTTON:

        if(state == GLUT_UP)
        {
            if (SphereSelected)
            {
                Cone=Cube=Torus=Teapot=false;
                Sphere=true;
                XSphere=x;
                YSphere=y;
                ZSphere=1;
                glutPostRedisplay();
            }

        }
    break;
    }
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB|GLUT_DEPTH);
   glutInitWindowSize (900, 900); 
   glutInitWindowPosition (0, 100);
   glutCreateWindow ("Scene Modeling and Interaction");
   init (); 
   glutDisplayFunc(display); 
   glutReshapeFunc(reshape);
   glutKeyboardFunc(keyboard);
   glutMouseFunc(MyMouse);
   glutMainLoop();
   return 0;
}

Answer 1

The x and y that the mouse function gives you are in screen pixel coordinates, not in the coordinates that your scene uses. In order to do this, you have to center your coordinates (by subtracting by half your screen size) and scaling them to about your screen size (by dividing them by something on the order of your screen size).

Thus, you probably want to do something like

XSphere = (x - 450) * 3.0 / 900;
YSphere = (450 - y) * 3.0 / 900;

and play around with the 3.0 until it gives you something reasonable.