 # Creating cylinder

Hi!

I’m absolute new to OpenGl and have the following question:

I’d like to draw a cylinder and specify the normal vectors for the lighting. I want to do this without the gluCylinder()-Methode.

Now I’m not sure how to start defining the coordinates for the cylinder.

enne

A perfect cylinder is two circles (the ends) separated by some distance with the middle space filled in. The best way to render one is to approximate the circles with triangles. Pick the number of slices of a circle you want to use (think slices of a pie), pick a radius, and pick a length of the cylinder.
Now, the coordinates of a circle are rsin(theta) and rcos(theta), so I’m going to use a for loop, increment theta, and use those values to construct the cylinder.
Something like this:

``````
int slices;
for(int i=0; i<slices; i++) {
float theta = ((float)i)*2.0*M_PI;
float nextTheta = ((float)i+1)*2.0*M_PI;
glBegin(GL_TRIANGLE_STRIP);
/*vertex at middle of end */ glVertex3f(0.0, halfLength, 0.0);
/* the same vertices at the bottom of the cylinder*/
glVertex3f(0.0, -halfLength, 0.0);
glEnd();
}

``````

Perfect, thanks todayman Cheers,

enne

One last question: I’m not sure how to create the normal-vectors. Can I use the same parameters as for the vertices?

The sides of the cylinder have normals that point away from the center, along what would be a radius, so those are (cos(theta), 0.0, sin(theta)), and the top/bottom faces straight up/straight down so those normals are (0.0, (-)1.0, 0.0).

Ok, thanks again!