I would like to visualize a curve when the blender game engine is running. In the editor the curve is clearly visible:
But when I run the game engine it is not
What can I do to visualize the curve when running the game engine
Curves are a unique object type, they won't render without depth in the default renderer and even with depth, they won't render in the BGE as these and paths aren't supported.
To render these, you have to convert to a mesh, use AltC > Mesh from Curve/Meta/.... You can always duplicate and move the original to another layer before converting so you have a backup and in most cases, if the converted mesh is simple enough, you can convert it back to a curve via the same menu.