Steve Sloan II [I knew you would be the fist to jump :-)] wrote:
>
>> I must be doing something _really_ stupid, but why I can't
>> draw even a simple tetrahedron with OpenGL? One of the faces
>> does not show :-/
>>
>> Is there any magic word that I must utter before it works?
>
> I have two guesses:
>
> 1) Could OpenGL be culling the back-facing polygons? Try
> changing GL_FRONT to GL_FRONT_AND_BACK in various places,
> and see if that fixes it.
>
No, the program behaved even more strangely with this.
> 2) How are you drawing the tetrahedron? Are you using
> GL_TRIANGLES,
>
Yes.
The program is as simple as possible, and all but the first
triangle appear correctly. The first triangle, however, is invisible.
Essentially, this is the OpenGL part of the program:
glLoadIdentity();
glTranslatef(0.0f,0.0f,-15.0f);
glRotated(m_angulo, m_x, m_y, m_z);
glBegin(GL_TRIANGLES); // Draw Triangles
glNormal3f(1.0f, 1.0f, 1.0f); // should be the yellow face, but is
invisible
glColor3f(1.0f, 1.0f, 0.0f);
glVertex3f(1.0f, 0.0f, 0.0f);
glVertex3f(0.0f, 1.0f, 0.0f);
glVertex3f(0.0f, 0.0f, 1.0f);
glColor3f(0.5f, 0.0f, 0.0f);
glVertex3f(0.0f, 0.0f, 0.0f);
glVertex3f(1.0f, 0.0f, 0.0f);
glVertex3f(0.0f, 1.0f, 0.0f);
glColor3f(0.0f, 0.5f, 0.0f);
glVertex3f(0.0f, 0.0f, 0.0f);
glVertex3f(0.0f, 1.0f, 0.0f);
glVertex3f(0.0f, 0.0f, 1.0f);
glColor3f(0.0f, 0.0f, 0.5f);
glVertex3f(0.0f, 0.0f, 0.0f);
glVertex3f(0.0f, 0.0f, 1.0f);
glVertex3f(1.0f, 0.0f, 0.0f);
glEnd();
glLoadIdentity(); // Reset
The interesting thing is that, if I begin with the Red Face,
then the Yellow Face becomes visible and the Red Face
becomes invisible.
Alberto Monteiro
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