Request: Add structure_render_layer to underground prototype

[Deadlock989]

Following these threads and the loader.structure_render_layer parameter that was added in early 0.17:

viewtopic.php?t=68165
viewtopic.php?t=66869
viewtopic.php?t=65627
viewtopic.php?t=68033

structure_render_layer is very welcome for loaders and I appreciate the difficulties (impossibilities?) in getting the 3D effect right in all cases for a 2D isometric game. However, I've been banging my head on this no-win wall for a year now and I think I finally see light at the end of the tunnel.

We can use structure_render_layer for loaders to change the rendering order. Tweaking them to a slightly higher level fixes the way they interact with undergrounds (UGs) but doesn't help with other cases. For example, if I have a mod where loaders routinely get placed right next to small furnace-type entities, I can set the render layer to "object" and all is well there - but doing that breaks the way loaders and undergrounds are layered:



So we have a devil's choice:

• Leave loaders on the default lower-object layer and have them look bad in front of both UGs and machines
• Set them to transport-belt-circuit-connector and have them look good in front of UGs but bad in front of machines
• Set them to object and have them look good in front of machines but bad behind UGs

If we could set the render layer for undergrounds as well to keep them on a par with what we're setting loaders to, and give them a small collision box to avoid the resulting clipping effects (0.2 is the setting I use on 1x1 loaders, which is enough to stop clipping but still allows players to run along belts), it would be win-win.

I understand why splitters and undergrounds have to be on a lower layer - because they don't have collision boxes and players want to run over them. The same is true for default non-graphicalised loaders, which are just a temporary decal. But now that undergrounds are quite large (approaching 1.5 tiles high), it already looks weird having players run over them, so I'd be quite happy to add a small collision box to them to avoid the clipping issues caused by setting them to be on the object layer, and it would make all these other order issues go away.

I can understand not wanting to change the base game defaults but it would be really, really nice to have the option to set both loader and underground structure_render_layer settings for modded scenarios (maybe splitters too but I don't personally have a use-case for that).