Re: Irregulars Question: OpenGL
Michael Harney wrote: I'm not familiar with OpenGL programming, but have used 3D programs and am familiar with vector mathematics. The only thing I can think of trying is to try reversing the point order on the first triangle (which should flip the normal vector) and see if that fixes the problem. No, it didn't. Alberto Monteiro ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: OpenGL
Steve Sloan wrote: I think you should get rid of the glNormal statement. No. No change at all :-( Alberto Monteiro ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Irregulars Question: OpenGL
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? Alberto Monteiro ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: OpenGL
Alberto Monteiro 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. 2) How are you drawing the tetrahedron? Are you using GL_TRIANGLES, or more complicated approaches like GL_TRIANGLE_STRIP or GL_TRIANGLE_FAN? If it's one of the latter two, you may be defining your points in the wrong order, which could either cause some triangles not to draw at all, or to flip the normal on one or more of the triangles, so they look like back-facing polygons (see (1)). __ Steve Sloan . Huntsville, Alabama = [EMAIL PROTECTED] Brin-L list pages .. http://www.brin-l.org Science Fiction-themed online store . http://www.sloan3d.com/store Chmeee's 3D Objects http://www.sloan3d.com/chmeee 3D and Drawing Galleries .. http://www.sloansteady.com Software Science Fiction, Science, and Computer Links Science fiction scans . http://www.sloan3d.com ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: OpenGL
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 ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: OpenGL
From: Alberto Monteiro [EMAIL PROTECTED] 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 I'm not familiar with OpenGL programming, but have used 3D programs and am familiar with vector mathematics. The only thing I can think of trying is to try reversing the point order on the first triangle (which should flip the normal vector) and see if that fixes the problem. Michael Harney [EMAIL PROTECTED] ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: OpenGL
On Tuesday 2004-02-17 06:57, Alberto Monteiro 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? Alberto Monteiro ___ http://www.mccmedia.com/mailman/listinfo/brin-l Dunno. Try: http://plug.phoenix.az.us/index.php Perhaps join: [EMAIL PROTECTED] Before escalating to an OpenGL discussion group. ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: OpenGL
Alberto Monteiro wrote: 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); I think you should get rid of the glNormal statement. It's not the correct normal for a flat triangle with the vertices you've given. If the object you want to create has perfectly flat faces, you should avoid specifying normals at all. Just let OpenGL automatically generate the correct normal. You should only specify normals if you're trying to create a smoothly curving object. __ Steve Sloan . Huntsville, Alabama = [EMAIL PROTECTED] Brin-L list pages .. http://www.brin-l.org Science Fiction-themed online store . http://www.sloan3d.com/store Chmeee's 3D Objects http://www.sloan3d.com/chmeee 3D and Drawing Galleries .. http://www.sloansteady.com Software Science Fiction, Science, and Computer Links Science fiction scans . http://www.sloan3d.com ___ http://www.mccmedia.com/mailman/listinfo/brin-l
