Limbs: Apply crawling score to prone movement cost

[dseguin]

Summary

None

Purpose of change

Fixes #54032.
Movement cost modifiers rely on having legs, even while prone. This means that characters without legs suffer maximum movement penalties even with perfectly functional arms.

Describe the solution

Add a crawling score and character modifier to determine movement cost while prone.

I'm far from an expert here, so hopefully someone can correct me on this. I've set the ability to crawl to be determined by:

• Arms (60% - 30% each arm)
• Legs (40% - 20% each leg)

When the character is prone, crawl_speed_movecost_mod applies to Character::run_cost instead of the regular run cost modifier. If the character is downed (not just prone), the crawl modifier is stacked on top of the regular move cost (instead of a flat x3 multiplier).

Describe alternatives you've considered

The values and modifiers are up in the air as far as accuracy goes. Thankfully those are easy to tweak. (again, I'm no expert)

Testing

Added unit tests to confirm the prone move costs below:

Encumbrance	No limb damage	Damaged arm (10 hp)	2 broken legs
None	600 moves	802 moves	1000 moves
30 (left arm)	660 moves	818 moves	1179 moves
37 (full body)	932 moves	1245 moves	1561 moves

Manual testing

At normal health, unencumbered (~6 seconds to move 1 tile):

With 43 arm encumbrance (~8 seconds to move 1 tile):

With a heavily damaged arm, unencumbered (~10 seconds to move 1 tile):

With a heavily damaged arm and 43 arm encumbrance (~12 seconds to move 1 tile):

At normal health, but with 2 broken legs (~10 seconds to move 1 tile):

Additional context

I mostly just wanted to demonstrate the jsonified scores/modifiers from #53069 :P

Ping: @Venera3. Do you have any thoughts about this?

[Venera3]

Nice! I'd raise the legs' contribution a bit, but in the game's context this distribution might work better. The one weirdness I can see is if hands/feet contribute you can't be immobilized barring encumbrance - minor parts don't have HP, so HP-scaled scores are kept at 100% even if the main part is broken. I haven't really decided how to deal with that in general, though.

[dseguin]

Good point! I'll leave hands and feet out of it for now.

[Holli-Git]

Wow I did not expect my issue to get fixed so quickly! Thank you!