Flags and Valid Placement Calculations

[vache]

https://github.com/CleverRaven/Cataclysm-DDA/blob/master/doc/JSON_FLAGS.md

Terrain, Furniture, & Traps

• Terrain: move_cost == 0 should prevent placement of furniture or traps. The flag FLAT may be enough for most things, but this is not exhaustive.
• Any furniture should prevent trap placement and vice versa.

Items:

• Terrain/Furniture: flags NOITEM DESTROY_ITEM prevent item placement. Note: this means things like vending machines and gas pumps will be forced to use the specials for placement.

Monsters & NPCs:

• Terrain: move_cost == 0 should prevent placement
• Furniture: move_cost_mod == -1 should prevent placement
• Traps: benign == true traps only

Vehicles:

• Only allow placement on FLAT or ROAD terrain with no furniture? Or TINY or NOCOLLIDE furniture/terrain?

Fields:

• No restrictions

Other flags we need to know:

• AUTO_WALL_SYMBOL for drawing walls correctly
• GOES_DOWN and GOES_UP for specials.

[vache]

Terrains are always placeable. If one is placed in a square with other incompatible features, the terrain should trump the other features and they should be reset to their null value. Order of preference should go terrain > furniture > trap > monster & monster groups > item & item groups > everything else. If something with higher preference is placed somewhere it is incompatible with something of lower preference, the higher one will get placed and overwrite the rest, otherwise the placement is not allowed.

[vache]

Gas Pumps (the specials) are terrain.

Signs, toilets, and vending machines are all furniture.

Placing one of the above should change the terrain/furniture to match, if placement is valid.