How to use face values in obj files (opengl c++)

Question

v 0.0 1.0 0.0
v -1.0 -1.0 -1 0
v 1.0 -1.0 -1.0
v 0 -1.0 1.0
f 2 4 3
f 4 2 1
f 3 1 2
f 1 3 4

I have an obj file that describes a tetrahedron polygon.

I've finished coding to parse those data and save them into arrays.

To use the vertex values, I simply had to use glVertex3f(x, y, z)

But I don't know what I should do to use the face values.

I tried to follow some tutorials, but all of them seem very different from each other and it's really confusing.

The ones that use vertex buffer objects are the ones you should be paying attention to. The ones that use glVertex3f and similar functions are using old+deprecated OpenGL. In particular, it's easy to render this face format with indexed rendering. — Colonel Thirty Two
– Colonel Thirty Two, Commented Apr 16, 2016 at 15:32

Jérôme · Accepted Answer · 2016-04-16 16:27:47Z

1

The face values tell you how use your vertices to create faces, for example, to create the first triangle (or face), from value f 2 4 3

 glBegin(GL_TRIANGLES);
  glVertex3f(-1.0f, -1.0f, -1 0f);    // vertex 2
  glVertex3f( 0.0f, -1.0f,  1.0f);    // vertex 4
  glVertex3f( 1.0f, -1.0f, -1.0f);    // vertex 3
glEnd();

You can find a complete example here, about create faces from vertices : http://math.hws.edu/graphicsbook/c3/s1.html#gl1geom.1.1

answered Apr 16, 2016 at 16:27

Jérôme

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