NewGRF House Spec Improvements

[2TallTyler]

There's been some discussion on Discord recently about improvements to the NewGRF house spec. Let's not lose these ideas.

(Each suggestion has its own post below, allowing replies to be made to that suggestion.)

[2TallTyler]

Larger multi-tile houses

Houses must have a substitute base game house ID, and multi-tile houses must use the IDs of a similarly-sized base game house. This limits available houses to 1x1, 1x2, 2x1, or 2x2 tiles.

It would be nice to allow GRF houses to be larger than 2x2 tiles.

[PeterN]

We could change the spec to allow multi-tile houses to use the same ID, but if that requires more map storage then it's actually better to just use consecutive IDs like now.

[2TallTyler]

Consecutive IDs are fine with a higher limit, more of an issue is requiring the substitute ID to be a base game house of the same size. There are also some hardcoded functions in town_cmd.cpp that would need to be adapted for larger multi-tile houses.

[PeterN]

Increase total number of house tile types.

I now have a patch for this that increases the limit to 4096, using 12 bits instead of 9 bits of map storage. More is possible I suppose...

[2TallTyler]

Yes, I was posting my next comment about this. 🙂

For reference, house IDs go up to 255, and (as you posted on Discord -- I haven't verified this) when multiple GRFs are used there's a total limit of 512 houses in a game. Multi-tile houses use one ID per tile.

[PeterN]

This is implemented with #12287 and #12288.

[2TallTyler]

Upgrade path callback

The biggest problem with multi-tile houses is that when a house is rebuilt, it is demolished and then a substitute house is randomly chosen to take its place. When a multi-tile house is demolished, the house which takes its place is often smaller, leading to the other tiles being filled in by other houses. This space will never again have a multi-tile house, because the space is gone.

We could add a callback, called when a house is about to be demolished, that allows that house to choose its replacement. Multi-tile houses could only allow other multi-tile houses to replace them, keeping that space reserved. This also allows for other fun features like house upgrades and modernization, and whatever else GRF authors can dream up. 😄

[nielsmh]

Allowing an upgrade/replacement callback to block the attempt to be replaced entirely might also have value. For example, if a building only available before 1930 (and maybe has an appropriate random seed) is attempted replaced in year 2030, i.e. has survived for a hundred years, it could block being replaced for "being historical". Of course that would not prevent players from demolishing it, which would be an entirely different concern.

[PeterN]

Why "of course"?

[zephyris]

... or allow removal of town buildings to build a multi-tile building?

[ldpl]

Town growth works on house count so allowing one building to replace many would affect growth poorly, effectively stopping it much sooner that current soft limit of around 25k houses. Though there is a possible solution of counting those removed houses and rebuilding them "for free", i.e. in addition to the regular growth loop.

[2TallTyler]

Allowing an upgrade/replacement callback to block the attempt to be replaced entirely might also have value.

We already have a callback for that, called protection in NML. ITL Houses uses it for historical districts already, often allowing a historical town center to be separate from the "new town" with skyscrapers that spawns elsewhere in a large city.

Unrelated but also interesting, there's also a destruction callback which attempts to destroy the house early.

[KeepinItRail]

Callback for type of service

Currently there is a callback which tells you if e.g. PASS have been delivered in current or previous month. Could there be a way to determine if this is road, rail etc service?

Thinking being a bus service is not good enough to allow skyscrapers, but a rail station would be.

[zephyris]

An alternative/simpler but related variables could be number of stations in the town, maybe broken down by station type, or number of company-owned tiles in the town. Subject to performance concerns of course.

[KeepinItRail]

This would work, especially for smaller towns, at the 'town level'.

I was thinking more along the lines of cargo_accepted_nearby_last_month(PASS) only in addition to cargo type, adding the transportation type, which would apply more at the station catchment level.

What might work instead is what you suggested, number_passengers_transported or combining with above for something like number_passengers_transported_nearby_last_month so you could 'localise' it to catchment area.

[KeepinItRail]

Population of nearby cities

Players often grow cities into each other, making a larger mega city. However the spec just allows you to get the population of city of the relevant tile. Is there a way to get the population of the larger mega city? E.g. return the population of all cities within n tiles.

[zephyris]

Height and bridging

It would be great if bridges could span over houses, so long as the house is short enough and the bridge is high enough. This is similar to behaviour of objects since OpenTTD 1.1, where a combination of an object flag and a height define if an object can have a bridge above it:

A building_flags (property 19) value allowing bridges over the house.

... paired with...

A height property for town houses (like property 16 for objects) defining the height of the house in heightlevels (8 pixels). This determines how high a bridge must be if it is allowed by the bit in property 19.

[zephyris]

Bridging should either always be disallowed for larger than 1x1 houses, to avoid supports in the middle of buildings. Alternative would be to not draw bridge supports, but that would add other graphical weirdnesses.

[reldred]

I don't think this is strictly necessary to automatically block on greater than 1x1 - an author could always use the property to disable bridges if they don't want a pillar in the midst of their multi tile house. For instance I intend on having carparks and industrial yards, and commercial plazas and other such things spawning in one of my sets and I forsee I may end up with multi-tile variations, and these would be quite fine to have a bridge support plopped in the middle of.

[zephyris]

More terrain variables for towns

Analogs of more house variables for towns, which would allow houses to access parent town properties which give context like elevation, hillyness, proximity to a coastline, etc. This would allow houses to only spawn in a hilly town in the desert, or a flat town near a coast, and give a unified appearance by deciding per town rather than per house.

This is essentialy implementing property 62 of houses for towns, giving them nearby_tile_slope, nearby_tile_is_water, nearby_tile_terrain_type, nearby_tile_water_class and nearby_tile_height.

[zephyris]

Town-wide cargo acceptance/production variables

It'd be nice for NewGRFs to access more information about how much cargo is produced and transported by towns. Currently, percent_transported_passengers and percent_transported_mail are available, but this is limited (and I'm not sure how this interacts with NewGRF industries).

number_transported_passengers and number_transported_mail would be useful. Variables for accepted_passengers and accepted_mail for the previous month would be useful. Or, even better, number_cargo and allow querying with an arbitrary cargo ID. Houses can also produce other cargos, and accessing the quantity produced of those cargos would be useful.

[2TallTyler]

percent_transported_passengers and _mail work fine with NewGRF industries.

House GRFs typically don't define cargo types, so I would use production effects to query transportation stats, from #11947.

[zephyris]

Wellll, maybe not publicly available House NewGRFs 😉. I've got some unpublished experiments with town houses acting like mini variable industries, which produce and consume non-passenger/mail/goods cargoes. More ways to query town production and acceptance would be nice.

[PeterN]

Town variables already exist for the amount of passengers/mail transported and produced, both this month and last month. These values don't interact with industry cargo acceptance/production at all.

Being able to specify a particular cargo type by parameter is feasible.

[nielsmh]

Presence and activity of nearby industries

Querying for the presence of either specific industries (maybe difficult to indicate which one you want) or industries meeting specific produces-cargoes/accepts-cargoes masks could let houses be selected by what kind of industry is present in or around a town. Maybe the presence of a Bank in the town would allow more office buildings to appear? Presence of a power plant in early years would give the town a more early-industrialized look? And so on.

[reldred]

I've thought long and hard about this, and I didn't think I had anything to add, but I think the only major thing I'd want beyond what some of the other folks have suggested is some additional properties/callbacks for setting whether when this building gets picked for creation is whether it can blow up everything in its path that would otherwise block it's construction. Optionally, I'd like to be able to specify whether it's allowed to knock down other 'protected' buildings. Perhaps also able to be tied to a callback so I can check the class id of a building to be knocked down so I don't accidentally clobber a 'monument'

Reason I'd want this? Large 2x2 buildings (and larger if we get them) can sometimes be difficult to spawn, and in particular if I'm trying to spawn in a new monument after a certain date, it can be hard to guarantee that it actually spawns.

[KeepinItRail]

I like this. Large 2x2 buildings better replacing smaller buildings in the city center as a city grows.

[zephyris]

Depth and tunneling

Like adding height and a flag to allow bridging, it might be interesting to have a flag which disallows tunneling under a house. This could be extended to have a depth, and tunnels would have to be at least that deep.

This could add nice flavour, eg. disallow tunnels under a landmark, or ensure tunnels are deep under buildings with basements
It also constrains building, nice to add options to restrict building to add complexity. Features tend to make building easier.

Could be extended to objects, industries too.