public override void drawLine( ref btVector3 from, ref btVector3 to, ref btVector3 fromColor, ref btVector3 toColor )
{
GL.Begin( PrimitiveType.Lines );
GL.Color4( fromColor.ToFloat4() );
GL.Vertex3( from.ToFloat4() );
GL.Color4( toColor.ToFloat4() );
GL.Vertex3( to.ToFloat4() );
GL.End();
}