How do I draw a cylinder in OpenTK(.Glu.Cylinder)?

Question

How do I draw a cylinder with OpenGL in OpenTK?

Answer 1

Sample code from an older project of mine. This creates an "uncapped" cylinder (top and bottom are empty).

int segments = 10; // Higher numbers improve quality 
int radius = 3;    // The radius (width) of the cylinder
int height = 10;   // The height of the cylinder

var vertices = new List<Vector3>();
for (double y = 0; y < 2; y++)
{
    for (double x = 0; x < segments; x++)  
    {
        double theta = (x / (segments - 1)) * 2 * Math.PI;

        vertices.Add(new Vector3()
        {
            X = (float)(radius * Math.Cos(theta)),
            Y = (float)(height * y),
            Z = (float)(radius * Math.Sin(theta)),
        });
    }
}

var indices = new List<int>();
for (int x = 0; x < segments - 1; x++)
{
    indices.Add(x);
    indices.Add(x + segments);
    indices.Add(X + segments + 1);

    indices.Add(x + segments + 1);
    indices.Add(x + 1);
    indices.Add(x);
}

You can now render the cylinder like this:

GL.Begin(BeginMode.Triangles);
foreach (int index in indices)
    GL.Vertex3(vertices[index]);
GL.End();

You can also upload vertices and indices into a vertex buffer object to improve performance.

Answer 2

Generating the geometry for a cylinder is quite simple (let's consider a Z-aligned cylinder). Let me use pseudocode:

points = list of (x,y,z)
    where x = sin(a)*RADIUS, y = cos(a)*RADIUS, z = b,
    for each a in [0..2*PI) with step StepA,
    for each b in [0..HEIGHT] with step StepB

About the indices: Let us assume N equal to the number of "levels" or "slices" of the cylinder (which depends on HEIGHT and StepB) and M equal to the number of points on every "slice" (which depends on StepA).

The cylinder contains some quads, each spanning 2 neighbouring slices, so the indices would look like:

indices = list of (a,b,c,d)
    where a = M * slice + point,
          b = M * slice + (point+1) % M,
          c = (M+1) * slice + (point+1) % M,
          d = (M+1) * slice + point
    for each slice in [0..N-2]
    for each point in [0..M-1]

If you need normals for the cylinder, they are simple to generate:

normals = (x/RADIUS,y/RADIUS,0)
    for each (x,y,z) in points

That's it for the round part of the cylinder, you might also want the "caps" but I believe they are easy to do.

I'll leave the fun part of translating my pseudocode into your language of choice for you. :)

The rest is to create/bind the VBO, load up the geometry, set pointers, use your shader of choice and call glDrawArrays(...) - any OpenGL 3 tutorial should cover this; are you familiar with that part?