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ankitmcgill

OpenGL Newbie help with Opengl

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ankitmcgill    122
Hi all, Before i post my question i should mention that i am a complete n00b to opengl or any 3d graphics package for that matter. So things might not be obvious to me ... i am trying to follow up the 'red book' and as im going on i try to code small programs to make sure i get the concepts. ive pasted the code for my program below .. what its supposed to do i think is show a train of parallel lines as viewed from a top perspective view. The window im using is 800x400. However when i run the program all i get is a blank screen. Im hoping someone can help me with this ... its driving me nuts ! glClearColor(0.0,0.0,0.0,0.0); //window clear color glClear(GL_COLOR_BUFFER_BIT); //clear the 'color buffer' glTranslatef(0,5,-5.0); //move the viewers eye +5(y) and -5(z) glMatrixMode(GL_PROJECTION); glLoadIdentity(); glFrustum(-1.0,1.0,-1.0,1.0,1.5,20); //define the viewing volume glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glViewport(0,0,800,400); //map the viewport onto the window 800x400 glBegin(GL_POINTS); glVertex3f(0,0,0); glVertex3f(0,0,1.5); glEnd(); int i=0; glBegin(GL_LINES); for(i=1;i<=16;i++) { glVertex3f(5*i/100,.5,1.5); glVertex3f(5*i/100,.5,10); } glEnd(); glFlush(); Thank you for all the help

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Brother Bob    10344
There are two issues which I immediately see. May be more of them though.

  • The call to glTranslate is probably placed at the wrong place. As it is, you translate, then you clear the matrix with glLoadIdentity after that. You probably want it after glLoadIdentity in the modelview matrix stack.

  • You're falling for integer division when calculating the coordinates. In the for-loop, try print the value of "5*i/100" and see what you actually get. 5*i is an integer multiplied by an integer, so the result is an integer. 5*i/100 is an integer divided by an integer, which performs integer division. Make any, or all, of the numbers a floating point value to force floating point division.

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