Effective engagement ranges

[mugling]

Summary

Effective range of guns is too low and unaffected by weapon type, skill, gunmods or aiming

If we define effective range as a 50% chance of a good hit on the first shot then effective range for the following guns used at different stages of the game is:

item	early	mid	late
Glock 19	3	3	3
MP5	3	3	3
AR-15	4	4	4

This explains why in DDA everyone walks around with a shotgun and a big handgun and engages targets at point-blank range. Rifles in particularly are especially useless.

The algorithm (with code sources) is set out below or otherwise skip to Plan.

Proof

Dispersion (σ) is expressed in minutes of arc and is the sum of penalties from
the player and their weapon. Player penalties are calculated as follows:

# Weapon and marksmanship skill 
(10 - WEAP) * 45  # Character::skill_dispersion()
(10 - GUN ) * 15  # Character::skill_dispersion()

# Player stats
(12 - DEX) * 15   # Character::ranged_dex_mod()
(12 - PER) * 15   # Character::ranged_per_mod()

# Clothing encumbrance
EYES  * 6         # player::get_weapon_dispersion()
HANDS * 6         # player::get_weapon_dispersion()

An additional penalty applies for recoil. The default is MIN_RECOIL of 150
with lower values achieved by aiming and higher values resulting from recoil.

We can calculate player dispersion (σ) for some typical survivors:

	description	GUN	WEAP	DEX	PER	EYES*	HANDS^	Pσ
S1	early game	2	2	8	8	5	0	630
S2	mid game	4	4	8	8	10	5	570
S3	late game	6	6	9	9	15	10	510

* safety goggles, light survivor mask, heavy survivor mask
^ fingerless leather gloves, light survivor gloves, survivor gloves

Weapon dispersion (Wσ) is simply the sum of the gun and ammo dispersion:

	description	GUN	AMMO	Wσ
G1	Glock 19	240	140	380
G2	MP5	150	140	290
G3	AR-15	5	80	85
G4	700NX + scope	60	15	75

Chance to hit (k) is calculated in Creature::projectile_attack as:

σ = Pσ + Wσ + recoil 
t = π / 180 / 60 * 0.745
k = range * σ * t

Excluding monster dodges this is applied in Creature::deal_projectile_attack:

k	result	multiplier
< 0.1	headshot	2.45 - 3.35
< 0.2	critical	1.75 - 2.30
< 0.4	good hit	1.00 - 1.50
< 0.6		0.50 - 1.00
< 0.8	grazing	0.00 - 0.25

Dispersion is applied randomly so resuming an even distribution the typical
effective dispersion (x̄σ) will be half and is calculated as follows:

x̄σ = ( Pσ + Wσ + recoil ) / 2

The below shows average dispersion (x̄σ) for some combinations:

	description	Wσ	recoil*	S1	S2	S3
G1	Glock 19	380	150	579	550	525
G2	MP5	290	150	536	506	476
G3	AR-15	85	150	432	402	372
G4	700NX + scope	75	0	352	322	292

* G1-G3 'from the hip' whereas G4 is after maximum aiming

If we define effective range as a 50% chance to yield a good hit (k<0.4) on the
first shot each of the following combinations has the following effective ranges:

	description	S1	S2	S3
G1	Glock 19	3	3	3
G2	MP5	3	3	3
G3	AR-15	4	4	4
G4	700NX + scope	5	5	6

These values are of course all (much) lower on subsequent shots due to the effects of recoil. I've included G4 as it illustrates both gunmods and aiming having very little overall effect.

Plan

Comments as to the following or alternative suggestions:

• pistol and shotgun are already well balanced having both limited range and being reasonably controllable in semi-auto mode.
• smg needs a small increase in range and a meaningful ability to use auto mode within this range.
• rifle needs an increase in range relative to all of the other groups
• Additional sights need to have more of an effect.
• Skill should provide more of an effect than just offsetting the inevitably better (and usually higher encumbrance) clothing that a player wears.

Implementation

TODO

[Firestorm01X2]

Finally someone pointed on this issue.

[TempestMaiden]

Hold on. Isn't "sight dispersion" a cap on how low the player can reduce recoil, not an additional source of fixed dispersion of its own?

But in general I'd have to agree that gun ranges leave something to be desired - throwing daggers shouldn't have significantly longer lethal ranges than SMGs.

[mugling]

Hold on. Isn't "sight dispersion" a cap on how low the player can reduce recoil, not an additional source of fixed dispersion of its own?

Good point - I've updated the above charts to represent this

[mugling]

Using the following definitions:

effective range
As 50% chance of a good hit (k<0.4) on the first shot at S2

maximum range
A 50% chance of any hit (k<0.8) after maximum aiming at S2

The current situation is as follows:

	example	effective	maximum
pistol	Glock 19	3	7
SMG	MP5	3	7
carbine	M4A1	4	10
rifle	M1 Garand	5	11

Note this is for the first shot only - subsequent shots will be much worse due to recoil. Also at maximum range many hits will do only 1-2 points damage even for otherwise good ammo.

What should these values be?

[DeadLeaves]

Not sure for the close range weapons, but for the longer range weapons its straight out silly that you cannot hit at longer distances. 15-20 squares at least for the rifles.
I once ran a bionic sniper just to try it out, and trying to snipe was still useless even when taking into account the massive bonuses you have as that profession.
With like 5 marksmanship and 5 rifles and I still have a hard time hitting STATIONARY turrets at military outposts with a scoped M82 and doing precision shots at distances like 20 squares

[mugling]

but for the longer range weapons its straight out silly that you cannot hit at longer distances. 15-20sqaures at least for the rifles.

One possible route is to bump MIN_RECOIL up and then allow rifles to aim more than pistols. Requiring them to aim to achieve long distance shots is both realistic and helps maintain balance as after the first shot your recoil is too high for you to take a second (long range) one any time soon whilst still allowing some shorter range use

[nikheizen]

Pistols are probably fine as is.
SMGs could do with either slightly increased range (5/10?) and/or heavily reduced recoil effect. You should be able to go full auto with an SMG, multiple rounds in a row and ream anything which isn't heavily armoured up close.
Rifles should definitely have an effective range of 15-20 squares and a max range of 30-35.
Carbines should have maybe 70% of this range.

Making aiming considerably more effective on longer ranged weapons is another good way of handling this. At 20 squares or so you have enough time.

[mugling]

max range of 30-35.

That's nearly a 10-fold increase on the current values and possibly too much although at maximum range your typical damage output is only 20% of effective range

[nikheizen]

10-fold increase

35 / 11 ~= 10 ?

Agree that it is probably too much though. My terminal wouldn't even be big enough to see what I'm shooting unless I displace my screen horizontally all the way. You should definitely be able to hit mobs ~20 or so tiles away with aiming an a good rifle though.

[mugling]

10-fold increase

Sorry my bad, I had compared the wrong numbers

[Firestorm01X2]

Maybe high skilled shooter should have effective range equal to maximum range (but only if shooter have time to aim).

I mean maybe it will be easier and much more logically to just increase effect of weapon skill on ability to hit target and at the same time increase aiming time.

[kevingranade]

In general I agree, but I think you're "overshooting" a bit, in particular
you're treating firing "from the hip" as a valid use case, it isnt. A 50%
chance to get a "good" hit at a range of roughly two meters sounds about
right for a beginner (skill levels at 2) irl, but since our shooting
distances are (intentionally) compressed, if anything it's too good.

The balance point should be around "aimed" shots (potentially also
considering "careful" and "precise").

The raison d'etre for the current aiming system is to limit firing rate,
especially the time between movement and firing, because previously "run
and gun" tactics were way too good.

Use cases (and ideally unit tests) around firing accuracy/range/etc should
include:
Target parameters (size, dodging)
Distance to target
Shooter abilities and penalties
Gun parameters
Shooter starting state (standing, moving, running, weapon holstered, weapon
out, in shooting stance, braced, prone)
Time to aim
Desired outcome (definite hit, good hit, crit, high DPS, etc)

If we're making any comparisons to real-world distances, we also need a
scaling factor for converting between irl and in game distances.

This is a lot of parameters, but neglecting some if these is going to
result in an incomplete rebalance meaning the whole thing will have to be
revisited later anyway. A lot of them can be specified with in-game
entities, which cuts down the configuration space. Some more can be handled
like you have already by specifying early/mid/late game survivor templates.

A basic example:
Target: zombie
Distance: 5 tiles (orthoganal)
Shooter: early game Shooter (slvl 2, OK stats, light encumbrance)
Weapon: Glock 19 (unmodded)
Start: standing, gun ready but not aimed
Time to aim: 2 seconds
Desired outcome: 50% chance of good hit

Target: brute
Distance: 40 tiles
Shooter: late game Shooter (slvl 8, OK stats, light encumbrance)
Weapon: browning blr (hunting rifle with scope)
Start: weapon ready, prone
Time to aim: unlimited
Desired outcome: 99%+ chance of headshot

Increasing max aim and requiring much more time to aim for long distance
shots sounds like a good idea for handling rifles. Also I'd be fine with
dismantling my goofy multi-sight handling logic, which would mean guns
configured for sniping would be even worse for close quarters, which is
good. I was trying to avoid the situation where "upgrading" a gun makes it
worse in critical ways, but in retrospect that was a bad idea.

[mugling]

Use cases (and ideally unit tests) around firing accuracy/range/etc should include:

This is the intention behind the definitions S1, S2, S3 etc and effective and maximum range. I'd like to work out agreed definitions...

Use cases (and ideally unit tests)

...then connect these to the stats dumper - especially as it can output to TSV for spreadsheet-fu. This should allow us to quickly identify any regressions as we work on this. Once it's worked out I might look at doing formal unit tests.

The balance point should be around "aimed" shots (potentially also considering "careful" and "precise").

in particular you're treating firing "from the hip" as a valid use case,

It's probably one of the most common use cases - a zombie suddenly appears. One possible option to maintain sane balance is to make more use of aim_speed. It's reasonable that a pistol should be quick to aim versus a rifle?

If we're making any comparisons to real-world distances, we also need a scaling factor for converting between irl and in game distances.

Might be best to avoid to avoid absolute distances as tiles vary in scale if their indoor vs outdoor. We can try and maintain relative proportion between different guns though.

Also I'd be fine with dismantling my goofy multi-sight handling logic, which would mean guns configured for sniping would be even worse for close quarters, which is good.

I don't think it's actually the cause of the problem. It's reasonable to have both a rail laser and scope. The issue is that the system isn't very intuitive to the player. It might be worth converting a lot of our display units from arc minutes to tiles or something of that nature

[TempestMaiden]

One obvious use case that should be considered:

It should be entirely possible for a gun-armed player to kill shockers or spitters from beyond their special attack range, at some level of skill; for throwing daggers this is possible at (and probably a bit before) throwing 7.

What requirements (in skills and equipment) should there be for firearms to do the same?

[DeadLeaves]

That really depends on the weapon. A survivor with relatively good weapon. say a rifle with a scope, should clearly if given time be able to take out such zombies. In fact this might be one of very few reasons I'd ever chose something like a rifle at all. And also one of the reason I only ever use sniper-ish weapons at immobile targets like turrets as it is now.

[kevingranade]

Use cases (and ideally unit tests) around
firing accuracy/range/etc should include:

This is the intention behind the definitions S1,
S2, S3 etc and effective and maximum range.
I'd like to work out agreed definitions...

Yep, just trying to clarify things.

Use cases (and ideally unit tests)

Connect these to the stats dumper -
especially as it can output to TSV for
spreadsheet-fu. This should allow us to
quickly identify any regressions as we work
on this. Once it's worked out I might look at
doing formal unit tests.

Unit tests should come first. It validates our assumptions about how stats
interact with the game code, provides a way to specify our end goals in an
unambiguous way, and sets the priority of completion correctly (i.e. more
important than the actual change, which it is).
If you make changes and then write unit tests that pass, you're just
documenting how it works now, which is entirely different from setting
goals and then making changes to meet them.

The balance point should be around "aimed"
shots (potentially also considering "careful"
and "precise").

in particular you're treating firing "from the
hip" as a valid use case,

It's probably one of the most common use
cases - a zombie suddenly appears.

Just because players want to react immediately doesn't mean they should
be able to. Taking time to aim is one of the biggest disadvantages of guns
vs melee weapons in close quarters, and we should preserve that.

One possible option to maintain sane balance
is to make more use of aim_speed. It's
reasonable that a pistol should be quick to
aim versus a rifle?

Absolutely, pistols should mitigate the aim speed penalty somewhat, but
guns should never be as fast as melee weapons in general (there are
outliers on both sides).
Another thing we could adjust is how quickly aiming increases aim,
currently it increases by a fixed amount per tick (adjusted by sight type),
but to make fine aiming harder to achieve, we could for example make the
improvement per tick reduce based on the current aiming level.

If we're making any comparisons to
real-world distances, we also need a scaling
factor for converting between irl and in
game distances.

Might be best to avoid to avoid absolute
distances as tiles vary in scale if their indoor
vs outdoor.

Tile sizes do not vary, ever. Yes our map features have wacky sizes, but
we do not treat indoor tiles differently from outdoor tiles.

We can try and maintain relative
proportion between different guns though.

The only reasonable way to do this I know of is to link weapon ranges to
their irl counterparts and then scale it. Having said that, there's no
pressing need for this set of changes to do this, I just wanted to mention
it because people are very likely to provide irl based use cases.

Also I'd be fine with dismantling my goofy
multi-sight handling logic, which would
mean guns configured for sniping would be
even worse for close quarters, which is
good.
I don't think it's actually the cause of the
problem. It's reasonable to have both a rail
laser and scope. The issue is that the system
isn't very intuitive to the player.

I don't think it's a cause, but it's a confounding variable and it reduces
the distinction between pistols and rifles.

It might be worth converting a lot of our
display units from arc minutes to tiles or
something of that nature

I'm against, MoA is a standard when talking about gun accuracy, and it
translates directly into the game with no adjustment.

It should be entirely possible for a gun-armed
player to kill shockers or spitters from beyond
their special attack range, at some level of
skill;

Yes, but this should happen by scaling shocker/spitter ranges, not gun
ranges.

[mugling]

Unit tests should come first.

To clarify these would be failing unit tests that we then adjust the code to pass? If so that could work well.

I'm against, MoA is a standard when talking about gun accuracy, and it translates directly into the game with no adjustment.

Sure but I can't do that amount of trig in the preamble without a calculator. MOA is a good comprative unit for guns, gunmod and ammo but perhaps an additional display along the lines of 'this gun has an effective range of x and maximum range of y' would be very helpful for new players.

[kevingranade]

Unit tests should come first.

To clarify these would be failing unit tests
that we then adjust the code to pass? If so
that could work well.

Yes, precisely this, the tests would be assertions of how we think it
should work.

I'm against, MoA is a standard when talking
about gun accuracy, and it translates directly
into the game with no adjustment.

Sure but I can't do that amount of trig in the
preamble without a calculator. MOA is a good
comprative unit for guns, gunmod and ammo
but perhaps an additional display along the
lines of 'this gun has an effective range of x
and maximum range of y' would be very
helpful for new players.

I thought you meant replacing it, effective and maximum range derived stats
would be great.

[Coolthulhu]

Reminder that this exists:

if( !gun.ammo_effects().count( "SHOT" ) ) {
    const item *parent = gun.is_gunmod() && has_item( gun ) ? find_parent( gun ) : nullptr;
    dispersion *= std::max( ( ( parent ? parent->volume() : gun.volume() ) / 3.0 ) / range, 1.0 );
}

This means that any gun with "expected range" of 4 must have volume no larger than 12.

Also, the biggest problem here is not absolute accuracy being too low/too high. It's the fact that accuracy itself is a sum rather than a product (or result of some other kind of accumulation) and is then multiplied by range (linearly).
As a result:

• Point blank attacks are nearly always the best
• Accuracy rises sharply near the endgame, but will never be enough for sniping by midgame (unless we count 6 tiles shotgun attacks as sniping)
• Gunmods have an extremely disproportionate effect on accurate guns (shotguns) compared to inaccurate guns. This is both bad for balance and for realism (a good grip should help more with a gun that "kicks", not less).
• Aiming only really makes sense when you aim to 100% achievable accuracy. There are no snapshots, except when counting moves. To fix this, aiming speed would have to depend way more heavily on current recoil (of the player), possibly linearly

We really need a dodge penalty on ranged attacks vs. dodgy critters. The one that calculates off bullet speed doesn't count, it isn't implemented properly yet since it is calculated off bullet speed.

[mugling]

What is the magic constant 0.745 in Creature::projectile_attack?

[Coolthulhu]

A way of preserving balance when changing units. Before, it was there in an implicit form, only indicated in a comment. Now it's explicit.

[mugling]

What was the change from and to? I'm trying to rework it as more standard isosceles trig so I wanted to either drop or rename that constant.

[Coolthulhu]

Not sure, it "was always there".
It might also have been a way of approximating the tangent (badly).

If you want to drop it, make sure the results don't get worse (less accurate) in the process. They're wild enough as it is, so magic constant is better than replacing it by 1.

[mugling]

It might also have been a way of approximating the tangent (badly).

It approximates a² = b² + c² - 2bc cosθ but the extra obscurity doesn't seem worth it versus just using the cosine formula

[kevingranade]

On Jul 11, 2016 5:22 PM, "Coolthulhu" notifications@github.com wrote:

Reminder that this exists:

if( !gun.ammo_effects().count( "SHOT" ) ) {
const item *parent = gun.is_gunmod() && has_item( gun ) ?
find_parent( gun ) : nullptr;
dispersion *= std::max( ( ( parent ? parent->volume() : gun.volume()
) / 3.0 ) / range, 1.0 );
}

This means that any gun with "expected
range" of 4 must have volume no larger than
12.

I'd be perfectly happy with this being replaced by something more sensible
like aim speed being modified by weapon weight or volume.

Also, the biggest problem here is not absolute
accuracy being too low/too high. It's the fact that accuracy itself is a
sum rather than a
product (or result of some other kind of
accumulation) and is then multiplied by range
(linearly).

Need an alternative that still makes sense, "it shouldn't be a sum" by
itself doesn't help.
I'm not trying to reject your point outright, just start a conversation
about it.

As a result:

Point blank attacks are nearly always the best

This should be the case. The only down side to firing at point blank is
the risk of letting yourvenemy get close. The only sensible way to correct
for this is to accentuate the risks of letting monsters get close.

Accuracy rises sharply near the endgame, but
will never be enough for sniping by midgame
(unless we count 6 tiles shotgun attacks as
sniping)

To snipe, you need:
A low dispersion gun (most rifles will qualify)

Gunmods have an extremely disproportionate
effect on accurate guns (shotguns)
compared to inaccurate guns. This is both
bad for balance and for realism (a good grip
should help more with a gun that "kicks", not
less).

This is because grips and some other gunmods have gotten a pass on the
general principle that everything contributes to dispersion, and all you
can do is eliminate sources of it. Grips are allowed to compensate for
arbitrary sources of dispersion. If we can add a heuristic for how much
dispersion in a particular gun stems from bad grips, and only allow
improved grips to compensate for that portion of it.

Aiming only really makes sense when you aim
to 100% achievable accuracy. There are no
snapshots, except when counting moves. To
fix this, aiming speed would have to depend
way more heavily on current recoil (of the
player), possibly linearly

You're saying make aiming slower with higher recoil, or faster with higher
recoil? The latter is what I meant by, "one thing we could adjust is how
quickly aiming increases aim". Now that I read that again, it's really
unclear, what I mean is spending more move points per point of dispersion
as dispersion gets small. Basically more diminishing returns for finer
aiming, and it also extends the range of useful times that can be spent
aiming. At the other end of the scale, this implies that going from,
"holding gun" to, "gun pointed in general direction of target" is nearly
instantaneous (but not instantaneous to overcome automatic fire).

We really need a dodge penalty on ranged
attacks vs. dodgy critters. The one that
calculates off bullet speed doesn't count, it
isn't implemented properly yet since it is
calculated off bullet speed.

Agreed, I thought we had one based on monster speed too, as an analogue for
dodginess.

BTW, it's laundry lists of issues like this that make me want to base any
rebalance on acceptance tests, discussion just breaks down for an issue
this complex, and details get lost.

[Coolthulhu]

This should be the case. The only down side to firing at point blank is the risk of letting yourvenemy get close.

A moving target close up needs faster movement to keep the aim on the target, can predict where you aim and avoid that and makes it impossible to rely on sights.
This isn't adequately represented in the current system, where a rifle scope improves the odds of scoring a headshot at point blank.

Point blanks shouldn't be the best thing around vs. dodgy enemies that, when up close, move faster than you can aim. For example, manhacks.

If we can add a heuristic for how much dispersion in a particular gun stems from bad grips, and only allow improved grips to compensate for that portion of it.

Even something as simple as "25% of base dispersion" would be fine. The problem is only really bad for very accurate guns, such as shotguns.

Now that I read that again, it's really unclear, what I mean is spending more move points per point of dispersion as dispersion gets small.

This would work if it got really high by the end.
The problem with current aiming is that you're almost always better off aiming perfectly.

I thought we had one based on monster speed too, as an analogue for dodginess.

We have/had it in 3 different "incarnations":

• In aim bar. This one was a bug, as it existed only on the aim bar and didn't have a mechanic behind it
• Speed giving bonus to dodge to monsters. This one was an ugly mechanic that didn't work well, so I removed it. It gave monsters with 140+ speed 1 dodge and those with 280+ speed 2 dodge. Prone to rounding and also hardcoded, so it was better to just specify it explicitly. I think there are like 2-3 monsters that actually used this bonus.
• Dodge roll against bullet speed. This one actually exists and makes throwing at manhacks harder. The problem is, it is vs. bullet speed and thus something that moves at half the speed of sound will still not be able to avoid being aimed at.

[kevingranade]

This should be the case. The only down side
to firing at point blank is the risk of letting
your enemy get close.

A moving target close up needs faster
movement to keep the aim on the target, can
predict where you aim and avoid that and
makes it impossible to rely on sights.

My mistake, I was over focusing on dispersion from gun/skill versus aim
dispersion. I agree that aiming should have a mechanic where monster
movement/dodging interferes with it.

This could either be an effect acquired when moving, or a passive property
of the monster.

If we can add a heuristic for how much
dispersion in a particular gun stems from
bad grips, and only allow improved grips to
compensate for that portion of it.

Even something as simple as "25% of base
dispersion" would be fine. The problem is only
really bad for very accurate guns, such as
shotguns.

Yeah, simple is fine, and it's certainly not worth a new gun stat.

Now that I read that again, it's really unclear,
what I mean is spending more move points
per point of dispersion as dispersion gets
small.

This would work if it got really high by the
end.

Yeah, it could get all the way out to a turn or more to extend effective
range by another square, which is perfectly fine if it allows you to take
shots effectively outside of combat.

[mugling]

it's laundry lists of issues like this that make me want to base any rebalance on acceptance tests,

Agreed, I have a near-working branch I'm hoping to push today that wraps some of the trig math into the startings of unit tests

[mugling]

Done