Add: [Script] Game script control of industry production level.

[michicc]

Motivation / Problem

Game scripts can override industry production in a limited way. They can prohibit production increases and/or decreases and prevent closure. But they can't actually change production, just hold it in place.

This half-way control isn't very useful if a GS wants to implement custom industry production rules.

Description

This PR adds GS API methods to get and set the production multiplier of an industry. NewGRFs are notified by a new flag in var 47 (GameScript control status). Setting the production multiplier does not prohibit industry closure, GS can use the existing control flag for this.

A script can optionally let OTTD generate a production change news message if needed.

Limitations

I'm not sure about the actual GS API. Maybe it would be better to use a magic prod_level value to restore the default production behaviour instead of the need to clear the control flag.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker

[andythenorth]

Works for me in initial (limited) test.

News message would be useful, but a separate call to GSNews.Create() does work. However, we do lack an appropriate GSNews::NewsType. NT_GENERAL and NT_ECONOMY aren't the right ones.

OpenTTD/src/news_type.h

Lines 21 to 39 in 9c262b0

	enum NewsType : byte {
	NT_ARRIVAL_COMPANY, ///< First vehicle arrived for company
	NT_ARRIVAL_OTHER, ///< First vehicle arrived for competitor
	NT_ACCIDENT, ///< An accident or disaster has occurred
	NT_ACCIDENT_OTHER, ///< An accident or disaster has occurred
	NT_COMPANY_INFO, ///< Company info (new companies, bankruptcy messages)
	NT_INDUSTRY_OPEN, ///< Opening of industries
	NT_INDUSTRY_CLOSE, ///< Closing of industries
	NT_ECONOMY, ///< Economic changes (recession, industry up/dowm)
	NT_INDUSTRY_COMPANY,///< Production changes of industry serviced by local company
	NT_INDUSTRY_OTHER, ///< Production changes of industry serviced by competitor(s)
	NT_INDUSTRY_NOBODY, ///< Other industry production changes
	NT_ADVICE, ///< Bits of news about vehicles of the company
	NT_NEW_VEHICLES, ///< New vehicle has become available
	NT_ACCEPTANCE, ///< A type of cargo is (no longer) accepted
	NT_SUBSIDIES, ///< News about subsidies (announcements, expirations, acceptance)
	NT_GENERAL, ///< General news (from towns)
	NT_END, ///< end-of-array marker
	};

[andythenorth]

Tested the version with news text option. Works, but the default news texts aren't going to be appropriate in most contexts (limited to 'expected to double', or 'falls by 50%') 😄

[andythenorth]

With the news flag set to false, seems a news message is triggered appropriately by the game without intervention?

(News log shows farm constructed, a news message following production increase by GS, and then GS posting a separate 'cabbage' message as a test).

EDIT: this was caused by an outdated version of FIRS grf which was triggering the news messages.

GSIndustry.SetProductionLevel(industry, GSIndustry.GetProductionLevel(industry) + 8, false);
// we issue the news message ourselves as of Jul 2023, this may or may not be needed depending on https://github.com/OpenTTD/OpenTTD/pull/11141
GSNews.Create(GSNews.NT_GENERAL, "Cabbage", GSCompany.COMPANY_INVALID, GSNews.NR_INDUSTRY, industry);

---

This comment doesn't have any effect on the (usually) inappropriate news messages emitted when news flag is set true.

[michicc]

Now with a custom news message option.

[andythenorth]

News message works, thanks :)

If show_news is false, null (or similar) must be passed as the parameter for custom_news.
Haven't checked if we have optional parameters for GS, but eh, possibly the docstring should mention this?

[2TallTyler]

I agree, the docstring should explain more explicitly what argument a GS author should pass if no news message is desired.

[michicc]

So something like If set to true and the production changed, generate a production change news message. If set to false, no news message is shown.?

If show_news is false, null (or similar) must be passed as the parameter for custom_news.

If show_news is false, any custom news text is simply ignored, so it can be null or some text. Unless you found some actual code bug where a message is still displayed.

[andythenorth]

If show_news is false, any custom news text is simply ignored, so it can be null or some text. Unless you found some actual code bug where a message is still displayed.

I verified that doesn't happen, show_news=false works as expected :)