How to draw a text on a cylindrical surface

First of all, add a text (on plane XY) and a cylinder to the scene:

Text text = new Text(Plane.XY, new Point2D(5, 25), "Eyeshot", 5);
model1.Entities.Add(text);
double radius = 20;

// if using Brep
Brep cylinder = Brep.CreateCylinder(radius, 50, 100);

// you can rotate it and translate it
cylinder.Rotate(0.5, Vector3D.AxisY, Point3D.Origin);
cylinder.Translate(0, 0, 10);
Plane pln = ((PlanarSurf)cylinder.Faces[1].Surface).Plane;        
model1.Entities.Add(cylinder,Color.FromArgb(150,Color.BlueViolet));

Then use the following code to create a text on a cylinder:

private void CreateCylindricalTextMesh(Plane pln,Text text, Model model1, double radius)
        {
            Align3D t = new Align3D(Plane.XY, pln);

            Mesh[] textMeshes = text.ConvertToMesh(model1);

            Mesh[] finalMeshes = new Mesh[textMeshes.Length];
            for (var i = 0; i < textMeshes.Length; i++)
            {
                Mesh m = (Mesh)textMeshes[i].Clone();
                m.LightWeight = false;
                for (int j = 0; j < m.Vertices.Length; j++)
                {
                    double x = m.Vertices[j].X;
                    double y = m.Vertices[j].Y;

                    Point3D pt = new Point3D(radius * Math.Cos(x / radius), radius * Math.Sin(x / radius), y);

                    pt.TransformBy(t);

                    m.Vertices[j] = pt;
                }

                finalMeshes[i] = m;
            }

            model1.Entities.AddRange(finalMeshes);
            model1.Invalidate();
        }

Cylinder as Mesh

If you have a Mesh instead of a Brep you must keep a Plane "synchronized" with that Mesh.

For example, if you rotate and translate the Mesh you have to apply the same transformation to that Plane:

double radius=10;
Mesh cylinder = Mesh.CreateCylinder(radius, 50, 100);
Plane pln = Plane.XY;

cylinder.Rotate(0.5, Vector3D.AxisY, Point3D.Origin);
cylinder.Translate(0, 0, 10);

pln.Rotate(0.5, Vector3D.AxisY, Point3D.Origin);
pln.Translate(0, 0, 10);

Then call the method in this way:

CreateCylindricalTextMesh(pln, text, model1, radius);

Final result: