Use collision layer to prevent unplaceable items on underground layers

[anythingapplied]

Add a custom collision layer, then add that layer to the underground surfaces (not sure if you'd have to do that on chunk load events), then go through and for every prototype not allowed, add the custom collision layer to its collision mask.

[anythingapplied]

You could even add "up-collison" to specific tiles that have entities on the surface above. This would let you "see" where an upstairs, for example, is placeable a bit better. Same thing for a "down-collision". So you'd probably need 3 custom collision layer.

[anythingapplied]

Looks like you can't create custom layers, but there are 5 unused layers available, "layer-11" through "layer-15"

https://lua-api.factorio.com/latest/Concepts.html#CollisionMaskLayer

[Daedeross]

• The first part of this suggestion (creating a mask for the un-allowed items) is plausible.
• The part about doing masks for above and bellow conflicts I think would be prone to issues.
  • It would involve inspecting every entity prototype to get it's bounding-box, then creating a version of the entity that is invisible and non-intractable but has collision on one of those layers. This would potentially double the number of entity prototypes in the game. I may be able to do some grouping of entities with the same or close to the same bounding boxes to reduce this, which seems tenable.
  • Every on_built event would have to be subscribed to and up to two of these 'phantom' entities would have to be placed down (one for the layer above, one for below). This will double to tippled--depending on how many entities are on the top and bottom layers--the number of entities in the game.
  • Also entities spawned from chunk generation (like trees), and other forces (like biters and nests) would have to be duped.
  • While this is potentially manageable, I think it would give too big of a performance hit to the game. Subterra is already quite resource intensive because it multiplies the number of chunks by 2-6 depending on settings.

[anythingapplied]

You mentioned the idea that you came up with to simply draw the above layer (when having an up block in your hand) onto the current layer is better. No affect on save size. No complexity with decimal bounding boxes. No conflicts with other mod's collision layers. Also, it has a huge advantage of being able to show you a larger area and not just the area your entity is currently on top of. You would just have to do a quick find_entities_filtered, and I guess maybe a find_tiles_filtered too.

I'm just not sure how to (or if you can) trigger that appropriately. I don't think there is a "take item into your hand" event, let alone the opposite. You may just have to add buttons to the GUI to show entities on the surface above and one to show entities below, which wouldn't be too bad of a way to do it.

[Daedeross]

This is what I have come up with so far:

It redraws once a second right now and doesn't seem to noticeably impact performance. I think I'll make this an option in the mod settings and add it to 0.6.0