OpenGL Cone Function Not Drawing Correctly - opengl

Question

I found an example online that shows how to draw a cone in OpenGL, which is located here: It was written in C++, and so I translated it to C#. Here is the new code:
public void RenderCone(Vector3 d, Vector3 a, float h, float rd, int n)
{
Vector3 c = new Vector3(a + (-d * h));
Vector3 e0 = Perp(d);
Vector3 e1 = Vector3.Cross(e0, d);
float angInc = (float)(360.0 / n * GrimoireMath.Pi / 180);
// calculate points around directrix
List<Vector3> pts = new List<Vector3>();
for (int i = 0; i < n; ++i)
{
float rad = angInc * i;
Vector3 p = c + (((e0 * (float)Math.Cos((rad)) + (e1 * (float)Math.Sin(rad))) * rd));
pts.Add(p);
}
// draw cone top
GL.Begin(PrimitiveType.TriangleFan);
GL.Vertex3(a);
for (int i = 0; i < n; ++i)
{
GL.Vertex3(pts[i]);
}
GL.End();
// draw cone bottom
GL.Begin(PrimitiveType.TriangleFan);
GL.Vertex3(c);
for (int i = n - 1; i >= 0; --i)
{
GL.Vertex3(pts[i]);
}
GL.End();
}
public Vector3 Perp(Vector3 v)
{
float min = Math.Abs(v.X);
Vector3 cardinalAxis = new Vector3(1, 0, 0);
if (Math.Abs(v.Y) < min)
{
min = Math.Abs(v.Y);
cardinalAxis = new Vector3(0, 1, 0);
}
if (Math.Abs(v.Z) < min)
{
cardinalAxis = new Vector3(0, 0, 1);
}
return Vector3.Cross(v, cardinalAxis);
}
I think I am using the parameters correctly(the page isnt exactly coherent in terms of actual function-usage). Here is the legend that the original creator supplied:
But when I enter in the following as parameters:
RenderCone(new Vector3(0.0f, 1.0f, 0.0f), new Vector3(1.0f, 1.0f, 1.0f), 20.0f, 10.0f, 8);
I receive this(Wireframe enabled):
As you can see, I'm missing a slice, either at the very beginning, or the very end. Does anyone know what's wrong with this method? Or what I could be doing wrong that would cause an incomplete cone?

Answer 1

// draw cone bottom
GL.Begin(PrimitiveType.TriangleFan);
GL.Vertex3(c);
for (int i = n - 1; i >= 0; --i)
{
GL.Vertex3(pts[i]);
}
GL.End();
That connects all vertices to each other and center but there is one connection missing. There is nothing the specifies connection from first to last vertex. Adding GL.Vertex3(pts[n-1]); after loop would add the missing connection.

Answer 2

The Solution was actually extremely simple, I needed to increase the number of slices by 1. Pretty special if you ask me.
public void RenderCone(Vector3 baseToApexLength, Vector3 apexLocation, float height, float radius, int slices)
{
Vector3 c = new Vector3(apexLocation + (-baseToApexLength * height));
Vector3 e0 = Perpendicular(baseToApexLength);
Vector3 e1 = Vector3.Cross(e0, baseToApexLength);
float angInc = (float)(360.0 / slices * GrimoireMath.Pi / 180);
slices++; // this was the fix for my problem.
/**
* Compute the Vertices around the Directrix
*/
Vector3[] vertices = new Vector3[slices];
for (int i = 0; i < vertices.Length; ++i)
{
float rad = angInc * i;
Vector3 p = c + (((e0 * (float)Math.Cos((rad)) + (e1 * (float)Math.Sin(rad))) * radius));
vertices[i] = p;
}
/**
* Draw the Top of the Cone.
*/
GL.Begin(PrimitiveType.TriangleFan);
GL.Vertex3(apexLocation);
for (int i = 0; i < slices; ++i)
{
GL.Vertex3(vertices[i]);
}
GL.End();
/**
* Draw the Base of the Cone.
*/
GL.Begin(PrimitiveType.TriangleFan);
GL.Vertex3(c);
for (int i = slices - 1; i >= 0; --i)
{
GL.Vertex3(vertices[i]);
}
GL.End();
}