Use OpenGL in Display Conduit

gistfile1.cs

[CommandStyle(Style.Hidden)]
public class TestOpenGlCallCommand : Command
{
  public override string EnglishName { get { return "TestGlCall"; } }
  protected override Result RunCommand(RhinoDoc doc, RunMode mode)
  {
    m_conduit.Enabled = !m_conduit.Enabled;
    doc.Views.Redraw();
    return Result.Success;
  }

  readonly MyGlConduit m_conduit = new MyGlConduit();
}

class MyGlConduit : Rhino.Display.DisplayConduit
{
  protected override void PreDrawObject(Rhino.Display.DrawObjectEventArgs e)
  {
    if (e.Display.IsOpenGL)
    {
      GL.glEnable(GL.GL_CLIP_PLANE0);
      double[] equation = new double[] { 1, 0, 0, 0 };
      GL.glClipPlane(GL.GL_CLIP_PLANE0, equation);
    }
  }
  protected override void PostDrawObjects(Rhino.Display.DrawEventArgs e)
  {
    if( e.Display.IsOpenGL)
      GL.glDisable(GL.GL_CLIP_PLANE0);
  }

}

static class GL
{
  public const uint GL_CLIP_PLANE0 = 0x3000;

  [System.Runtime.InteropServices.DllImport("opengl32.dll")]
  public static extern void glEnable(uint cap);

  [System.Runtime.InteropServices.DllImport("opengl32.dll")]
  public static extern void glDisable(uint cap);

  [System.Runtime.InteropServices.DllImport("opengl32.dll")]
  public static extern void glClipPlane(uint plane, double[] equation);
}