[Bug]: Wallclock mode minutes per year setting does not work correctly for values other than 0 and 12

[JGRennison]

Version of OpenTTD

master

Expected result

Wallclock mode minutes per year setting does what it says on the tin

Actual result

At minutes per year = 12, a calendar day is 74 ticks
At minutes per year = 13, a calendar day is 153 ticks
At minutes per year = 24, a calendar day is 221 ticks

TimerGameCalendar::sub_date_fract counts from 0 to ((74 * min_per_year) / 12) - 1
then date_fract counts from 0 to 74

Steps to reproduce

Use the minutes per year setting

[2TallTyler]

Yikes! I changed this algorithm immediately before merge after using a different one for months, and apparently failed to properly test it.

For anyone looking into this, here's the relevant code: https://github.com/OpenTTD/OpenTTD/blob/master/src/timer/timer_game_calendar.cpp#L106-L119

The original algorithm scaled the number of date_fract ticks in a day. @TrueBrain rejected that because we expose date_fract to GRFs and shouldn't break their assumptions that it only goes to 74 before resetting. Our discussion resulted in sub_date_fract. (I am absolutely not throwing TB under the bus here, my bugs are my fault! Just trying to give some background.)

This whole algorithm probably needs to be rewritten from scratch, because it's broken in several ways.

I will do some thinking about this, but if anyone else has any ideas, feel free to chime in! 🙂