[wesnoth-commits] [wesnoth/wesnoth] c560b0: Add attribute apply_to_vision to [effect]apply_to=...

[Steve Cotton]

  Branch: refs/heads/master
  Home:   https://github.com/wesnoth/wesnoth
  Commit: c560b0efab63eb012bff8dcece6385db69bab99d
      https://github.com/wesnoth/wesnoth/commit/c560b0efab63eb012bff8dcece6385db69bab99d
  Author: Steve Cotton <steve at octalot.co.uk>
  Date:   2021-05-13 (Thu, 13 May 2021)

  Changed paths:
    M changelog.md
    M data/schema/units/modifications.cfg
    M data/test/scenarios/test_effect_on_vision.cfg
    M src/units/unit.cpp
    M wml_test_schedule

  Log Message:
  -----------
  Add attribute apply_to_vision to [effect]apply_to=movement

When processing [effect]apply_to=movement, if apply_to_vision is 'yes'
(which is the default) then the vision points will change by the same amount.
Previously, it sometimes affected vision and sometimes didn't; for most cases
where it makes a difference, I expect it to be a change from unanticipated
behavior to expected behavior.

Please refer to the new unit test added in this commit for more detailed docs;
that test is also a rough draft for the Wiki update needed when this merges.

The reason it sometimes affected vision was that the special value of -1 vision
points was interpreted as "use the value of the max movement points instead".
The special value of -1 is still supported and frequently used, and refactor that
is out of scope for this commit - it's easy to check when the code path changed
in this commit is used, however it's considerably more complex to find all
routes that create a unit with vision set to -1.

I'm expecting one add-on, Rebirth In Nature, to need a large update for this;
as well as a trivial change needed to the Add Creature Pack.

There are several mods that have their own handling for vision, recalculate the
values frequently, and are expected to continue working as before, as they'll
just overwrite any changes that the engine makes.
* Proper Flying Mod / Proper Vision Mod
* LotI
* Blessed Altar Mod
* Shards Era's `CALCULATE_WEAPONS_ONLY` macro
* Castle of Evil Spirit

Rebirth In Nature is an RPG-style campaign that expects the player's unit to
have vision separated from movement along with right-click menus that change
the character's movement, this will probably need `apply_to_vision=no` in
many places. OTOH, its `item_id=mobility` uses `apply_to=movement` followed by
`apply_to=vision` to implement in 1.14 what this change will make default
behavior in 1.16.

There are a few sharpshooter units which have vision better than their
movement. If given a buff which boosts their movement, this will give
them a buff to vision too; likely a change towards expected behavior.
* Archaic Era's Royal Ranger
* Ageless Era's Royal Ranger and Dwarvish Forest Sniper
* Eastern Europe at War's Yacht and Great Yacht
* Era of More Units's Lone Wolf
* Southernerns has several sharpshooters
* WWII Era has several sharpshooters
* War of Dominions has some guard towers with very low movement

Silver Age has abilities that modify vision based on time-of-day, but unlike
the Proper Flying Mod and LotI these are done by adding and removing objects
that add or subtract one vision point, these should be unaffected by this
change. Unrelated to that, it declares values for `[unit_type]vision=` even
when the value is the same as max moves - like the sharpshooters this means
that buffs to their movement wouldn't have buffed their vision but now do.

There are few units with vision less than movement. Generally these seem to be
missile weapons that are represented as units, and they probably won't meet any
apply_to=movement statements - even if a movement power-up is available, the
player would probably choose a different unit.

The Add Creature Pack has two creatures (the Cactose Elder and Carnivore Fatal
Plant) that have reduced vision, along with AMLAs that increase those units'
movement; these AMLAs will need to use `apply_to_vision=no`. These two
creatures are used in Castle of Evil Spirit, but they won't get enough
experience to get an AMLA there.

Fixes #3356.