Rubber arrow helper and more arrows

[Philippe Hurbain]

Hello Magnus.

These "parts" are special. No real bricks so rules for real bricks do not necessarily apply here. And your questions are perfect examples of such differencies: arrows are 2D because they are used more as "illustrations" in some instruction step (think about BUFFER EXCHANGE or look into original LEGO instructions for examples). 

I agree that 3D arrows actually look weird for this usage!

For this reason we do not want to render them 3D and do not want to show edges of 3D object either. So both these points you mentioned are intentional.

As we don't want the edges, the simplest is to remove all type 2 lines! I don't think even that condlines (type 5) are useful here.

However, we do not want to create any problems with rendering so we should be always sure, for example, that these parts have both sides (top and bottom). This is what needs to be improved before publishing these files in the official library, as I noted above.

The simplest is to add a BFC NOCLIP statement before all surfaces.