Question

So I am trying to learn how to use glViewport(), “MULTIPLE TIMES”. Below is my code, I have tried to follow others examples, but they are either so convoluted with other things not relevant to what I am doing or, I do not understand what they are doing. By the way I am using glut to manage my windowing system. So the best way for me to learn is to get a simple example running for myself, then extrapolate from there. Below is my code for a simple program that divides the screen in two and draws two identical spheres, I can’t figure out why the sphere on the right is getting stretched when gluPerspective() is identical for both view ports. Please, if you could just explain to me what I am doing wrong in my code it would greatly help. Outside resources are great, but i need simple, simple examples (not Nate Robinson examples).

GLfloat width = 800, height = 600, x_0 = 470, y_0 = 0;
int mainWindow;


    void resize(int w, int h){
         width=w;
         height=h;
    }

    void draw(void){
         glEnable(GL_SCISSOR_TEST);
         glClearDepth(1.0);
         glClearColor(0.0, 0.0, 0.0, 1.0);
         glEnable(GL_DEPTH_TEST);
         glEnable(GL_LIGHT0);
         glEnable(GL_LIGHTING);
         GLfloat color[4] = {1.0, 0.0, 0.0, 1.0};

         /*
          * LEFT VIEW PORT
          */
         glMatrixMode(GL_PROJECTION);
         glLoadIdentity();
         glViewport(0, 0, (float)width/2 , height);
         gluPerspective(45, ((float)width/2)/(float)height, 1, 2000);
         glMatrixMode(GL_MODELVIEW);
         glScissor(0, 0, (float)width , height);
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
         glLoadIdentity();
         gluLookAt( 0.0, 0.0, 50.0,
                    0.0, 0.0, 0.0,
                    0.0, 1.0, 0.0 );

         glPushAttrib(GL_LIGHTING_BIT | GL_CURRENT_BIT); 
         glPushMatrix();
         glMaterialfv(GL_FRONT, GL_DIFFUSE, color);
         glutSolidSphere(10.0, 20, 40);
         glPopMatrix();
         glPopAttrib();

         /*
          * THE SECOND VIEW PORT
          */
         glMatrixMode(GL_PROJECTION);
         glLoadIdentity();
         glViewport((float)width/2, 0, width , height);
         gluPerspective(45, ((float)width)/2/((float)height), 1, 2000);
         glMatrixMode(GL_MODELVIEW);
         glScissor(((float)width/2), 0, width , height);
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
         glLoadIdentity();
         gluLookAt( 0.0, 0.0, 50.0,
                    0.0, 0.0, 0.0,
                    0.0, 1.0, 0.0 );
         glPushAttrib(GL_LIGHTING_BIT | GL_CURRENT_BIT); 
         glPushMatrix();
         glMaterialfv(GL_FRONT, GL_DIFFUSE, color);
         glutSolidSphere(10.0, 20, 40);
         glPopMatrix();
         glPopAttrib();

         glDisable(GL_SCISSOR_TEST);
         glFlush();
         glutSwapBuffers();
    }

    void glutAppInitialize(void){
         GLfloat light_ambient[] = {0.2, 0.2, 0.2, 1.0};
         GLfloat light_diffuse[] = {1.0, 1.0, 1.0, 1.0};
         GLfloat light_specular[] = {1.0, 1.0, 1.0, 1.0};
         GLfloat light_position[] = {1.0, 1.0, 0.0, 0.0};
         glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);
         glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);
         glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);
         glLightfv(GL_LIGHT0, GL_POSITION, light_position);
    }

    int main(int argc, char* argv[]){
         glutInit(&argc, argv);
         glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
         glutInitWindowPosition(x_0, y_0);
         glutInitWindowSize(width ,height);
         glutAppInitialize();
         mainWindow = glutCreateWindow("Tori App");
         glutDisplayFunc(draw);  
         glutReshapeFunc(resize);
         glutMainLoop();
         return(0);
    }

Note that I am playing around while I wait on a response, I got it to do what I wanted, but the solution makes no since, please see the lines of code, basically I moved the view ports start position to 1/4 of the screen instead of on half and I am no longer dividing by two on gluperspective.

/*
 *  THE SECOND VIEW PORT
 */

    glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glViewport(width/4, 0, width , height);
gluPerspective(45, ((float)width)/(((float)height)), 1, 2000);

Answer 1

The second pair of arguments to glViewport are width and height, not the ending x/y position. Your second glViewport should be glViewport(width/2, 0, width/2, height)