Cube doesn't rotate

[ramy1989]

Here I am trying to draw a cube with three faces.One face is red, one green and one blue.
Then I rotate the cube in a way that I should see half of the red face and half of the green face, of 45 degrees around the y axis.I should see a half red and half green cube, but I only see the red face, that's the code:

#import <OpenGL/OpenGL.h>
#import <GLUT/GLUT.h>
 
 
int width=500, height=500, depth=500;
 
 
void init()
{
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glEnable(GL_DEPTH_TEST);
    glViewport(0, 0, width, height);
    glOrtho(0, width, height, 0, 0, depth);
}
 
 
void display()
{
    glClearColor(0.9, 0.9, 0.9, 0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glBegin(GL_QUADS);
    gluLookAt(250, 250, 0, -250, 250, 250, 0, 1, 0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glRotatef(45, 0, 1, 0);
 
    // First face
    glColor4f(1, 0, 0, 0);
    glVertex3i(100, 100,0);
    glVertex3i(300, 100,0);
    glVertex3i(300, 300,0);
    glVertex3i(100, 300,0);
 
    // Second face
    glColor4f(0, 1, 0, 0);
    glVertex3i(300,100,0);
    glVertex3i(300,300,0);
    glVertex3i(300,100,300);
    glVertex3i(300,100,300);
 
    // Third face
    glColor4f(0, 0, 1, 0);
    glVertex3i(100, 100,300);
    glVertex3i(300, 100,300);
    glVertex3i(300, 300,300);
    glVertex3i(100, 300,300);
 
    glEnd();
    glFlush();
}
 
 
int main(int argc, char * argv[])
{
    glutInit(&argc, argv);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(width, height);
    glutCreateWindow("Test");
    glutDisplayFunc(display);
    init();
    glutMainLoop();
    return 0;
}

PS: Code outdated because my university is outdated

[Dan Bartlett]

You need to switch the positions of:

gluLookAt(250, 250, 0, -250, 250, 250, 0, 1, 0);

and

glMatrixMode(GL_MODELVIEW);

since the first time display is called you will still be in GL_PROJECTION matrix mode, so it will mess up your projection matrix.

It should probably read:

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(250, 250, 0, -250, 250, 250, 0, 1, 0);

[ramy1989]

I modified the code this way:

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(250, 250, 0, -250, 250, 250, 0, 1, 0);
glRotatef(45, 0, 1, 0);

But I still see only a red face.
Also, I really can't understand when to be in modelview mode and when in projection mode.When I rotate, translate and scale I am in modelview mode, but for the other functions, how to know if I must use them in mdoelview or projection mode?

[ramy1989]

I reviewed the code and got this way to draw an entire cube:

#import <OpenGL/OpenGL.h>
#import <GLUT/GLUT.h>
 
 
int width=500, height=500, depth=500;
 
 
void init()
{
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glEnable(GL_DEPTH_TEST);
    glViewport(0, 0, width, height);
    glOrtho(0, width, height, 0, -depth, depth);
}
 
 
void drawCube()
{
    glBegin(GL_QUADS);
 
    glColor4f(1,0,0,0);
    glVertex3i(100, 100, 0);
    glVertex3i(300, 100, 0);
    glVertex3i(300, 300, 0);
    glVertex3i(100, 300, 0);
 
    glVertex3i(100, 100, 300);
    glVertex3i(300, 100, 300);
    glVertex3i(300, 300, 300);
    glVertex3i(100, 300, 300);
 
    glColor4f(0, 1, 0, 0);
    glVertex3i(100, 100, 0);
    glVertex3i(100, 100, 300);
    glVertex3i(100, 300, 300);
    glVertex3i(100, 300, 0);
 
    glVertex3i(300, 100, 0);
    glVertex3i(300, 100, 300);
    glVertex3i(300, 300, 300);
    glVertex3i(300, 300, 0);
 
    glColor4f(0, 0, 1, 0);
    glVertex3i(100, 100, 0);
    glVertex3i(100, 100, 300);
    glVertex3i(300, 100, 300);
    glVertex3i(300, 100, 0);
 
    glVertex3i(100, 300, 0);
    glVertex3i(100, 300, 300);
    glVertex3i(300, 300, 300);
    glVertex3i(300, 300, 0);
 
    glEnd();
}
 
 
 
 
void display()
{
    glClearColor(0.9, 0.9, 0.9, 0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glRotatef(45, 1, 1, 0);
    drawCube();
    glLoadIdentity();
    glFlush();
}
 
 
 
 
int main(int argc, char * argv[])
{
    glutInit(&argc, argv);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(width, height);
    glutCreateWindow("Test");
    glutDisplayFunc(display);
    init();
    glutMainLoop();
    return 0;
}

And it does rotate.