colored cube

Has anyone got any idea why this cube changes colors??

here is the code



#include <GL/glut.h>
double f=0.3,d = 0.01,j=1,angel = 29;;
GLfloat vertices[][3] = {{-1,-1,-1},{1,-1,-1},
{1,1,-1},{-1,1,-1},{-1,-1,1},
{1,-1,1},{1,1,1},{-1,1,1}};
GLfloat colors[][3] = {{0.0,0.0,0.0},{1.0,0.0,0.0},{1.0,1.0,0.0},{0.0,1.0,0.0},{0.0,0.0,1.0},{1.0,0.0,1.0},{1.0,1.0,1.0},{0.0,1.0,1.0}};
GLfloat light_pos[] = {0.0,1.0,0.0,0.0};
GLfloat diffuseMaterial[4] = { 0.5, 0.5, 1.5, 1.0 };
GLfloat diffuseMaterial2[4] = { 1.5, 0.0, 1.5, 1.0 };
GLfloat diffuseMaterial3[4] = { 1.5, 1, 1.5, 0.0 };
GLfloat diffuseMaterial4[4] = { 1, 1, 1, 1.0 };
GLfloat light_ambient[] = { 0.0, 0.0, 0.0, 1.0 };

void polygon(int a,int b,int c ,int d)
{

glBegin(GL_POLYGON);
glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial);

glVertex3fv(vertices[a]);glNormal3f(1.0,1.0,1.0);
glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial2);
glNormal3f(0.0,1.0,0.0);
glVertex3fv(vertices);
glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial3);
glNormal3f(0.0,0.0,1.0);
glVertex3fv(vertices[c]);
glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial4);
glVertex3fv(vertices[d]);
glEnd();
}


void display()
{





glClearColor(0,0,0,1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glLoadIdentity();
glColor3f(1,0.0,0.0);
//glLightfv(GL_LIGHT0,GL_POSITION,light_pos);
glRotatef(angel,1,1,1);


polygon(0,3,2,1);
polygon(2,3,7,6);
polygon(0,4,7,3);
polygon(1,2,6,5);
polygon(4,5,6,7);
polygon(0,1,5,4);






glFlush();
glutSwapBuffers();
angel+=1;

glutPostRedisplay();
}
void reshape(int x, int y)
{ glViewport(0,0,x,y);glEnable(GL_DEPTH_TEST);

glMatrixMode(GL_PROJECTION); glLoadIdentity();
glOrtho(-2.0 * (GLfloat)x/ (GLfloat) y,2.0 * (GLfloat) x/ (GLfloat) y,-2.0
,2.0,-10.0,10.0);

glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);


glMatrixMode(GL_MODELVIEW);



}


int main(int argc, char** argv)
{
glutInit(&argc,argv);
// Need double buffering for animation
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
// Create and position the graphics window
glutInitWindowPosition(0, 0);
glutInitWindowSize(500, 500);
glutCreateWindow("Solar System Demo";
// Set up callback functions

glutDisplayFunc(display);
glutReshapeFunc(reshape);

glutMainLoop();
return 0;
}

#include <GL/glut.h>
#include <math.h>

double f=0.3, d = 0.01, j=1, angel = 29;

GLfloat vertices[][3] = {
{-1,-1,-1}, {1,-1,-1},
{1,1,-1}, {-1,1,-1},
{-1,-1,1}, {1,-1,1},
{1,1,1}, {-1,1,1}
};

GLfloat diffuseMaterial[4] = { 0.5, 0.5, 1.5, 1.0 };
GLfloat diffuseMaterial2[4] = { 1.5, 0.0, 1.5, 1.0 };
GLfloat diffuseMaterial3[4] = { 1.5, 1, 1.5, 0.0 }; // completely transparent color
GLfloat diffuseMaterial4[4] = { 1, 1, 1, 1.0 };

void cross(const GLfloat u[], const GLfloat v[], GLfloat w[])
{
w[0] = u[1]*v[2] - u[2]*v[1];
w[1] = u[2]*v[0] - u[0]*v[2];
w[2] = u[0]*v[1] - u[1]*v[0];
}

void normalize(GLfloat w[])
{
float d = 0.0; int i;

for (i=0; i< 3; i++) d+= w*w;
d = sqrt(d);

if (d > 0.0)
for(i=0; i < 3; i++)
w /= d;
}

void polygon(int a,int b,int c ,int d)
{

glBegin(GL_POLYGON);

// your normals were wrong - recalculating them is overkill, but I was in a hurry.
GLfloat n[3];
cross(vertices[a], vertices, n);
normalize(n);
glNormal3fv(n);

glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial);
glVertex3fv(vertices[a]);

glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial2);
glVertex3fv(vertices);

glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial3);
glVertex3fv(vertices[c]);

glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial4);
glVertex3fv(vertices[d]);

glEnd();
}

void display()
{
glClearColor(0,0,0,1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glLoadIdentity();
// glColor3f(1,0.0,0.0); // achieves nothing if lighting is enabled
glRotatef(angel,1,1,1);

polygon(0,3,2,1);
polygon(2,3,7,6);
polygon(0,4,7,3);
polygon(1,2,6,5);
polygon(4,5,6,7);
polygon(0,1,5,4);

glFlush();
glutSwapBuffers();
angel += 1;

glutPostRedisplay();
}

void reshape(int x, int y)
{
glViewport(0,0,x,y);
glEnable(GL_DEPTH_TEST);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(
-2.0 * (GLfloat)x/ (GLfloat) y,2.0 * (GLfloat) x/ (GLfloat) y,
-2.0
,2.0,
-10.0,10.0
);

glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);

glMatrixMode(GL_MODELVIEW);
}


int main(int argc, char** argv)
{
glutInit(&argc,argv);
// Need double buffering for animation
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
// Create and position the graphics window
glutInitWindowPosition(0, 0);
glutInitWindowSize(500, 500);
glutCreateWindow("Solar System Demo";
// Set up callback functions

glutDisplayFunc(display);
glutReshapeFunc(reshape);

glutMainLoop();
return 0;
}

Thanks man

What exactly does glNormal3fv(n); do?

sorry for the delayed post (was focusing on cos311) the glNormal functions specify the normal vector to use for all subsequent glVertex calls. these are ignored if lighting is off, which is why we didn't need to worry about them early on in the course. with flat shading OpenGL only uses the normal defined for the first vertex on a face. and for smooth shading it uses the normal at every vertex to calculate a colour at that vertex, it then linearly interpolates the colours between the vertices (this is gourad shading).