#openttdcoop

NotRoadTypes Spec

Essential
‘road' and ‘tram' are independent, like ‘road’ and ‘rail’
they can coexist on the same tile in some cases, but do not influence each other
the term ‘roadtypes’ is confusing for historical reasons and due to pre-existing use in code, and is not used here: this is NotRoadTypes
‘tram’ and ‘road’ are built as subtypes
per tile, one subtype of ‘road’ and one subtype of ’tram’ may be present
construction tools for ‘road’ and ’tram' are independent
adding/removing/converting ‘road’ on a tile does not affect ‘tram’ for tile and vice-versa
vehicles are either ‘road’ or ‘tram’, they cannot be both
vehicle routing and movement per ‘road’ and ‘tram’ are independent
any ‘road’ subtype may be freely combined with any ’tram’ subtype, there are no ways to make ‘road’ and ’tram’ incompatible with each other by subtype or any other means 
subtypes
proposed up to 15 ‘road' subtypes and 15 ‘tram’ subtypes (implementation detail: uses 4 bits each, uses 8 bits free in m8)
15 is more than enough for any game
spec shouldn’t have an opinion on how many type a game needs, but 3 or 4 of each is plenty imho
each subtype has a label
vehicle compatibility with a subtype is determined by label
vehicle may determine some properties by subtype (power, possibly others)
drawing
‘tram’ is always drawn above ‘road’; authors need to be aware of this when drawing sprites, no mechanism will be provided to vary this
drawing of city roads, bridges, tunnels, and similar will follow existing behaviour
drawing of rail crossings may or may not be fixed (road tile is enforced for tram crossings currently, this looked non-trivial to fix when I tried)
methods _may_ be provided to enable more control over appearance, e.g. snow above snowline etc
catenary
subtypes can provide catenary, or not (implementation detail: flag or cb returning sprites)
both ‘road’ and ‘tram’ can provide catenary on a tile
authors will need to draw catenary carefully to avoid it looking bad when ‘road’ and ‘tram’ catenary are combined on a tile
vehicle power on a tile is determined by vehicle against subtype label, unrelated to drawing of catenary sprites
there is sophisticated handling of rail catenary to preserve continuity where railtypes cross, something similar needs to be provided for NotRoadTypes
converting between subtypes
a convert tool is needed, similar to rail conversion
this will need to consider ownership carefully
too restrictive = can’t overbuild subtypes in towns
too permissive = deliberate or accidental breaking of existing routes by overbuilding incompatible subtype
drive-in stops:
behaviour of articulated vehicles and trams unchanged, can’t use drive-in stops
catenary needs to be provided for ‘road' drive-in stops
overtaking: out of scope

Optional (proposed by frosch)
split global toolbar to ‘road’ and ‘light rail’
this makes the distinction between the transport types obvious
in this way it’s clear that a tile can have
1 type of rail
1 type of road
1 type of light rail
unknown: would the various vehicle menus, station menus etc also be split for ‘road’ and ‘light rail’?

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