Rendering a Cube?

Hello,

I have been working on drawing primitives using glBegin(GL_QUAD) and glEnd(). I’m specifically trying to render a simple cube.

However, upon rendering only the first two faces render, the next four don’t render at all. I’m not sure why, because the data itself is right, and upon printing to console window the data looks right, yet the other four sides don’t seem to want to render. The first two sides render perfectly.

I’ve color coded each face so that I know which side is being rendered, and have commented out the normals for now.

Anyone have any ideas? I’m sure I’m not doing something at the most basic level!

I placed the key code below.

Many thanks!

CODE:

struct face {
GLint a;
GLint b;
GLint c;
GLint d;
};

struct Vert {
GLfloat i;
GLfloat j;
GLfloat k;
GLfloat x;
GLfloat y;
GLfloat z;
};

Vert verts[8] = {
{ 0.577349185944,0.577349185944,-0.577349185944,
1.0,1.0,-1.0 },
{ 0.577349185944,-0.577349185944,-0.577349185944,
1.0, -1.0, -1.0 },
{ -0.577349185944,-0.577349185944,-0.577349185944,
-1.0,-1.0,-1.0 },
{ -0.577349185944,0.577349185944,-0.577349185944,
-1.0,1.0,-1.0 },
{ 0.577349185944,0.577349185944,0.577349185944,
1.0,1.0,1.0 },
{ 0.577349185944,-0.577349185944,-0.577349185944,
1.0,-1.0,1.0 },
{ -0.577349185944,-0.577349185944,0.577349185944,
-1.0,-1.0,1.0 },
{ -0.577349185944,0.577349185944,0.577349185944,
-1.0,1.0,1.0}
};

face faces[6]={
{0, 1, 2, 3},
{4, 7, 6, 5},
{0, 4, 5, 1},
{1, 5, 6, 2},
{2, 6, 7, 3},
{4, 0, 3, 7}
};

void display(void)
{
/* clear all pixels */
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

/* draw white polygon (rectangle) with corners at

• (0.25, 0.25, 0.0) and (0.75, 0.75, 0.0)
  */
  glRotatef(60.0, 1.0, 0.0, 0.0);
  //glRotatef(45.0, 0.0, 1.0, 0.0);
  for (int i=0;i<6;i++) {
  if (i == 0)
  glColor3f(1.0,0.0,0.0); // Red
  else if (i == 1)
  glColor3f(0.0,1.0,0.0); // Green
  else if (i == 2)
  glColor3f(1.0,1.0,0.0); // Yellow
  else if (i == 3)
  glColor3f(0.0,0.0,1.0); // Blue
  else if (i == 4)
  glColor3f(1.0,0.0,1.0); // Magenta
  else
  glColor3f(0.0,1.0,1.0); // Cyan
  glBegin(GL_QUADS);
  //glNormal3f(verts[faces[i].a].i,verts[faces[i].a].j,
  verts[faces[i].a].k);
  glVertex3f(verts[faces[i].a].x,verts[faces[i].a].y,
  verts[faces[i].a].z);
  //glVertex3fv(verts[faces[i].a]);
  //glNormal3f(verts[faces[i].b].i,verts[faces[i].b].j,
  verts[faces[i].a].k);
  glVertex3f(verts[faces[i].b].x,verts[faces[i].b].y,
  verts[faces[i].a].z);
  //glNormal3f(verts[faces[i].c].i,verts[faces[i].c].j,
  verts[faces[i].a].k);
  glVertex3f(verts[faces[i].c].x,verts[faces[i].c].y,
  verts[faces[i].a].z);
  // glNormal3f(verts[faces[i].d].i,verts[faces[i].d].j,
  verts[faces[i].a].k);
  glVertex3f(verts[faces[i].d].x,verts[faces[i].d].y,
  verts[faces[i].a].z);
  glEnd();
  }

/* don’t wait!

• start processing buffered OpenGL routines
  */
  glFlush ();
  }

Did you glEnable(GL_DEPTH_TEST)?

Yes, in the code below. Note, it does render the first two sides.

void init (void)
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glShadeModel(GL_SMOOTH);
glEnable(GL_DEPTH_TEST);
}

did you define the vertice-indices of the faces in the right order ?
render the thing with glDisable(GL_CULL_FACE)
when it works, you defined the faces wrong

–styx

Thanks both of you for your suggestions.

I just implemented glDisable(GL_CULL_FACE) and it had no effect.

Btw, I was under the impression that the depth buffer would deal with the issue of z ordering, so that it wouldn’t matter the order of rendering. Is that right?

P.S. I’m rendering on a Win2000 platform, and I just tried the same code on Win98, and it gives the same results.

Thanks again.

glVertex3f(verts[faces[i].b].x,
verts[faces[i].b].y, verts[faces[i].a].z);
*

Notice the letter ‘a’ marked with star. Should’t it be ‘b’. You have same typo in every glVertex3f call.

Good catch, Spartacus. I should have caught that one.

Works just fine now.

Thanks.