Giving 2D structures 3D depth [duplicate] - opengl

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How to give a 2D structure 3D depth
Hello everyone,
I posted this same question yesterday. I would like to have uploaded images showing my program output but due to spamming protection I am informed I need 10 reputation "points". I could send images of my output under different projection matrices to anyone willing.
I am beginning to learn OpenGL as part of a molecular modeling project, and currently I am trying to render 7 helices that will be arranged spatially close to each other and will move, tilt, rotate and interact with each other in certain ways.
My question is how to give the 2D scene 3-Dimensional depth so that the geometric structures look like true helices in three dimensions?
I have tried playing around with projection matrices (gluPerspective, glFrustum) without much luck, as well as using the glDepthRange function. As I understand from textbook/website references, when rendering a 3D scene it is appropriate to use a (perspective) projection matrix that has a vanishing point (either gluPerspective or glFrustum) to create the illusion of 3 dimensions on a 2D surface (the screen)
I include my code for rendering the helices, but for simplicity I insert the code for rendering one helix (the other 6 helices are exactly the same except for their translation matrix and the color function parameters) as well as the reshape handler.
This is the output ![enter image description here][1] I get when I run my program with an orthographic projection (glOrtho) and it looks as a 2D projection of helices (curved lines drawn in three dimensions). This is my output (![enter image description here][2]) when I use a perspective projection (glFrustum in my case). It does not appear as if I am looking at my helices in 3D!!
Perhaps the glFrustum parameters are wrong?
//GLOBALS
GLfloat x, y, z;
GLfloat c = 1.5f; //helical pitch
GLfloat theta; //constant angle between tangent and x-axis
thetarad = theta/(Pi/180.0); //angle converted from degrees to radians
GLfloat r = 7.0f; //radius
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST); /* enable depth testing */
glDepthFunc(GL_LESS); /* make sure the right depth function is used */
/*CALLED TO DRAW HELICES*/
void RenderHelix() {
/**** WHITE HELIX ****/
glColor3f(1.0,1.0,1.0);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glTranslatef(-30.f, 100.f, 0.f); //Move Position
glRotatef(90.0, 0.0, 0.0, 0.0);
glBegin(GL_LINE_STRIP);
for(theta = 0; theta <= 360; ++theta) { /* Also can use: for(theta = 0; theta <= 2*Pi; ++rad) */
x = r*(cosf(theta));
y = r*(sinf(theta));
z = c*theta;
glVertex3f(x,y,z);
}
glEnd();
glScalef(1.0,1.0,12.0); //Stretch or contract the helix
glPopMatrix();
/* Code for Other 6 Helices */
.............
glutSwapBuffers();
}
void Reshape(GLint w, GLint h) {
if(h==0)
h=1;
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
GLfloat aspectratio = (GLfloat)w/(GLfloat)h;
if(w<=h)
//glOrtho(-100,100,-100/aspectratio,100/aspectratio, -50.0,310.0);
//glOrtho(-100,100,-100/aspectratio,100/aspectratio, 0.0001,1000000.0); //CLIPPING FAILSAFE TEST
//gluPerspective(122.0,(GLfloat)w/(GLfloat)h,10.0,50.0);
glFrustum(-10.f,10.f, -100.f/aspectratio, 100.f/aspectratio, 1.0f, 15.0f);
else
//glOrtho(-100*aspectratio,100*aspectratio,-100,100,-50.0,310.0);
//glOrtho(-100*aspectratio,100*aspectratio,-100,100,0.0001,1000000.0); //CLIPPING FAILSAFE TEST
//gluPerspective(122.0,(GLfloat)w/(GLfloat)h,10.0,50.0);
glFrustum(-10.f*aspectratio,10.f*aspectratio,-10.f,10.f, 1.0f,15.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}

Answer 1

The usual reason that simple 3d applications don't "look 3d" is because you need to set up a lighting system. Lighting is a major source of depth cues to your brain.
Here's a good tutorial on adding lighting to an OpenGL program:
http://www.cse.msu.edu/~cse872/tutorial3.html
EDIT: For more context, here's the relevant chapter from the classic OpenGL Red Book:
http://fly.cc.fer.hr/~unreal/theredbook/chapter06.html
Notice the screenshot near the top, showing the same sphere render both with and without lighting.

Answer 2

I agree it's difficult if you can't post your images (and it may not be trivial then).
If your code is open source you are likely to get help for molecular modelling from the Blue Obelisk Community (http://blueobelisk.shapado.com/ is a SE-type site for answering these questions).
There used to be a lot of GL used in our community but I'm not sure I know a good code which which you could hack to get some idea of the best things to do. The leading graphics tools are Jmol (where the gfx were largely handwritten and very good) and Avogadro which uses Qt.
But if you ask for examples of open source GL moelcular graphics you'll probably get help.
And of course you'll probably get complementary help here