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POGiving 2D structures 3D depth
 

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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/4947733/how-to-give-a-2d-structure-3d-depth">How to give a 2D structure 3D depth </a> </p> </blockquote> <p>Hello everyone, </p> <p>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. </p> <p>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.</p> <p>My question is how to give the 2D scene 3-Dimensional depth so that the geometric structures look like true helices in three dimensions?</p> <p>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)</p> <p>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. </p> <p>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!! </p> <p>Perhaps the glFrustum parameters are wrong? </p> <pre><code>//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 &lt;= 360; ++theta) { /* Also can use: for(theta = 0; theta &lt;= 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&lt;=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(); </code></pre> <p>}</p>
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