How to display a sphere correctly in openGL

The main problem you are having here is Z clipping. The initial Z range for the scene is (-1, 1) so you only see a part of the actual sphere and by change in its size you go out of z range.

Image

There are several problems I see in the code. It is good to get a grasp of how the GLUT workflow actually works.

Lets see what the code does wrong.

Main

int main(int argc, char **argv) { srand(time(NULL)); init(); glutInit(&argc, argv); glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA); glutInitWindowPosition(50, 30); glutInitWindowSize(glutGet(GLUT_SCREEN_WIDTH) - 80, glutGet(GLUT_SCREEN_HEIGHT) - 60); mainWindow = glutCreateWindow("New Window"); //global variable WIDTH = glutGet(GLUT_WINDOW_WIDTH); //global variable HEIGHT = glutGet(GLUT_WINDOW_HEIGHT); //global variable glutDisplayFunc(renderScene); 

Here you define the display function. It is called every time the window contents has to be invalidated. In this case it is invalidated only at start. The renderScene function does not do anything awesome, just clears the screen. So you get a black screen at the beginning.

 glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); 

No need for blending at the moment. You can skip that part altogether.

 glutTimerFunc(50, timerProc, 0); 

Now you set up the timerProc function to be called in 50 milliseconds.

 glutMainLoop(); 

As the documentation states: glutMainLoop enters the GLUT event processing loop. This routine should be called at most once in a GLUT program. Once called, this routine will never return. It will call as necessary any callbacks that have been registered.

 return 0; } 

Render Scene

void renderScene() { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 

This is the only place where you clear the screen. Timer Func does not do this.

 glLoadIdentity(); 

You are reseting the matrices.

 // Set the camera gluLookAt(1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f); 

Setting up the matrices. (One matrix to be precise)

 glutSwapBuffers(); 

And without drawing anything you swap buffers.

} 

Scene rendering function is called each time the window frame has to be redrawn.

Timer

This function does rely on the screen being cleared at first by the renderScene. void timerProc(int arg) { glutTimerFunc(50, timerProc, 0);

 // Reset transformations glLoadIdentity(); // Set the camera gluLookAt(1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f); glClearColor(1.0f, 1.0f, 1.0f, 1.0f); 

Not clearing this time. Only setting the color.

 glColor3f(0.0, 0.0, 0.0); //color = black glPushMatrix(); glTranslated(0, 0, 0); glutSolidSphere(.74, 500, 500); glPopMatrix(); glutSwapBuffers(); } 

How to fix it?

Just setup the matrices. With proper Z range.

void resetTransformations() { glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-1, 1, -1, 1, -1000, 1000); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); gluLookAt(1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f); } void renderScene() { glClearColor(1.0f, 1.0f, 1.0f, 1.0f); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Reset transformations resetTransformations(); // Just to see some triangles glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); glColor3f(0.0, 0.0, 0.0); //color = black glPushMatrix(); glTranslated(0, 0, 0); glutSolidSphere(0.74, 500, 500); glPopMatrix(); glutSwapBuffers(); } int main(int argc, char **argv) { srand(time(NULL)); glutInit(&argc, argv); glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA); glutInitWindowPosition(50, 30); glutInitWindowSize(256, 256); mainWindow = glutCreateWindow("New Window"); //global variable WIDTH = glutGet(GLUT_WINDOW_WIDTH); //global variable HEIGHT = glutGet(GLUT_WINDOW_HEIGHT); //global variable glutDisplayFunc(renderScene); glutIdleFunc(renderScene); glutMainLoop(); return 0; }