I'm working on my first project using openTk. I'm creating virtual arcball for 3D model rotation. It works fine, but I need to add circle which won't rotate with model. This circle should visualize arcball.
My code to achieve rotation is:
private void SetCamera()
Matrix4 scale = Matrix4.Scale(magnification / diameter);
Matrix4 translation1 = Matrix4.CreateTranslation(-center);
Matrix4 rotation = Matrix4.CreateFromAxisAngle(axisOfRotation, angleOfRotation*(float)numericSensitivity.Value);
Matrix4 translation2 = Matrix4.CreateTranslation(0.0f, 0.0f, -1.5f);
oldRotation *= rotation;
rotationChanged = false;
modelview = translation1 * scale * oldRotation * translation2;
So I would like to ask if there is some way how to draw circle, which wil be unaffected by this rotattion (will be on same position on a screen).