Strategy Games
By Chris DiPaolo
What Are Strategy Games
• Strategy game:
– The majority of challenges presented are strategic conflict challenges.
– Victory is attained by superior planning and taking the optimum
actions.
– Elements of chance must not play a large role of the game.
– Other challenges such as tactical, logistical, economic and exploration
may also be present in the game.
– Physical challenges play little to no part.
– Games are more symmetric than the games in other genres and so are
somewhat easier to balance for difficulty.
Game Features
• Strategy games fall into two main subgenres:
– Classical turn-bases games
• Ex/
– Sid Meier’s civilization series
– Total War
– Heros of Might And Magic
– Real-time strategy games.
• Ex/
– Starcraft series
– Warcraft series
– Company of Heros
Classical turn-bases games
• Pure Strategy games then tend to be Turn
based rather then operating in Real-time
• Players may mull over their moves,
considering benefits of one choice over
another
– This can result in a frustrating “analysis paralysis” ,
this is were players take a long time considering
possible moves while players wait.
– To avoid this design the game so that all players
can choose there next move simultaneously.
Real-Time Strategy(RTS) games
• Was developed after turn-based games
• RTS adds time pressure to strategy games
because everything happens at once
• Players do not have individual turns to ponder
moves.
• RTS requires player to keep a sharp lookout
and to think quickly
Challenges
• Strategy games may include challenges such
as:
– Economic
– Exploration
– Strategic conflict (dominates)
• Without strategic conflict game becomes a construction
and management simulation.
Strategic Conflict
• Conflict is most often characterized as combat between
groups of individual combatants.
• Combatants are known as units
• Units
– Are can be anything from an ancient warrior to spacecraft.
– Not all units have to fight EX/ transport
– Units don’t have to be moveable EX/ A fixed Gun
• Specialized units
– Are often portrayed as buildings that produce units
– Can be destroyed if attacked and be repaired by repair
units
– This will be referred to as factories
Strategic Conflict Cont.
• Each unit and factory is under the players control
and provide some benefit to him.
• Units may be atomic(no individual parts) or
compound, with separate parts that can be
added and removed and perhaps destroyed
without completely destroying the whole unit.
• Each unit behaves according to particular
performance characteristics like
– How long it can survive when under attack
– How rapidly it can fire a weapon,
– how fast it can move
Strategic Conflict Cont.
• Most war games seek to reproduce the classic
situations and tactics of military combat.
• These tactics include:
–
–
–
–
–
Flanking manoeuvre's
Sneak attacks
Creating diversions
Cutting off enemy supply lines
Killing the superior officers to leave troops without
leadership
– Taking advantage of the effects of bad weather.
Alternative To Combat
• Conflict does not necessarily involve physical
combat.
• More advance games include elements of:
– Diplomacy, crisis management and espionage
Exploration Challenges
• Exploration lets players investigate unknown
terrain in a game world.
• Fog Of war: is two techniques:
– Unexplored regions are shown in black
– Explored regions but no patrolled regions shown
dimly
Exploration Challenges Cont.
• The Fog of war lends realism and excitement to the
game, and rewards player set up guard units to warn of
impending invasions and those who send out scouts to
find out where the enemy is.
• Some games will show the map dimly to allow players
to plan more effectively.
– Ex StarCraft series
• Many games cheat by allowing the computers AI to
see the landscape but not the player.
– This technique is used to compensate if the AI isn't very
good.
– Good design solution to a programming problem
Economic Challenges
• In Strategies games at the beginning of a level,
player has to obtain recourses that the player
can convert to units later on.
• When Designing you may supply the players
with limited resources at the beginning of the
game and place more out in the landscape for
discovery.
• Try to avoid unlimited resource for the game
could in principle go on forever.
Economic Challenges cont.
• It is vitally important that the economic
productivity of all sides be equally balanced,
or economic advantages will rapidly outweigh
strategic skill.
– To accomplish this make the map layout fairly
symmetrical Ex/ StarCaft 2, Age of empires
Economic Challenges cont.
• More complicated games use several different
recourses.
– Ex/ Age Of Empires
– Players must obtain:
» Food
» Wood
» Stone
» Gold
Player Actions
• The players role is that of a commander or
manager, so most actions consist of orders to
units.
• Giving orders is a 2 step process:
– Player selects the unit or units that will receive the
order.
– Player issues the order, either by clicking
somewhere in the landscape, on an enemy unit,
or on a button or menu item.
Player Actions Cont.
•
Move
–
•
Attack
–
•
Units will move to safety that leaves the unit more vulnerable while moving but units move faster.
Dash
–
•
used to produce new units by consuming recourses.
Retreat
–
•
Sets formation of troops for tactical purposes.
Produce
–
•
This command tells units to attack any enemy that comes into range, but don’t purse it if retreats.
Establish Formation
–
•
This order countermands both attack and movement orders.
Hold
–
•
Unit advances until the enemy units is in range. Then open fire, and pursues if enemy retreats.
Stop
–
•
Unit uses pathfinding AI to find its way there, taking the quickest route while avoiding obstructions
Unit does not attempt to attack but tries to get to its destination as quickly as possible.
Patrol
–
A cycle movement between two or more designated points.
Core Mechanics
Designing Units
Rock-Paper-Scissors (RPS) Model
• RTS models are easy to implement and naturally
balanced.
• This is only suited for simple games and should be
avoid in modern war games with large number of units
types.
• This model does not does not take into account
battlefield conditions. EX/ knight sneaks up behind a
archer.
• Instead create numerical attributes that describe the
combat strength and weakness of unit types
independly
Numeric Attributes
• The most commonly used numerical attributes in war
games include the following:
– Heath(HP)
• This is reduced as units take damage
• Once HP reaches zero the unit is considered dead.
• Amour also measured in heath points which can absorb all damage or
reduce damage dealt to the unit
– Units may have zero or more weapons which to attack enemy
units
• A weapon inflicts damage in individual instance called shots.
• The amount of damage it does per shot is called shot power
(expressed in HP per shot).
• Rate of fire- the minimum of shots per minute
• If the game models ammunition consumption for a certain weapons.
Then the weapon has a certain amount of ammo.
Numeric Attributes Cont.
– Range
• Is the maximum distance at which a weapon can deliver damage.
• Units that have no hand-to-hand combat and will need minimum range. Were if below the
weapon is not functional.
• Gun emplacements cannot always point in all directions. This this case you will need to define
transverse arc.
– Projectiles
• Small projectiles such as bullets and arrows should only hit one enemy unit each.
• Larger projectiles like cannonballs. You will need to define the shot mass and shot velocity
• Explosive projectiles on the other hand require a blast radius. This is the measure of distances
from the landing point to the blast radius
– Accuracy
•
•
•
•
Is the measure of chance that a given weapon will hit the point at which it is aimed.
This is expressed as real numbers between 0 (never hits) and 1(always hits)
Theoretical accuracy is the average accuracy of a weapon under all conditions.
Practical accuracy is the add to or subtract to from the Theoretical accuracy based on the
conditions.
Numeric Attributes Cont.
•
Defensive dogging
– Units ability to successfully dodging solid projectiles such as bullets.
– Like accuracy, this should be expressed as a real number between 0 to 1.
•
Speed
– Is the rate the unit move
– Each unit has a maximum speed that represents the fastest they can move over unrestricted
terrain.
– Speed should also be affected by the difficulty of the terrain which is represented as 0-1.
•
Turn Rate
•
Describes the rate at which a unit can turn to face a new direction. This applies both to moving and
fixed units.
•
Range of vision
– If your game includes fog of war you will need a number that describes range of vision.
Numeric Attributes Cont.
• DESIGN RULE – no invincible units
– Avoid designing any units whose weapon range
and maximum speed attributes are both greater
than the range and speed of any enemy units it
may face.
Special Capabilities
• Many units in strategy game have special
capabilities that strongly affect the tactics and
strategy of play.
• Here is a short list of possibilities:
–
–
–
–
–
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Stealth units
Flying or sailing
Repair
Transport
Constructing buildings and producing mobile units
Leadership
Computing the relative value of units.
• If your game allows players to purchase units or construct new units. You
will need to decide on the relative cost of each type of unit.
• The following are two equations that serve as first approximation of the
military effectiveness of units
– Attack unit value = maximum heath * shot power * rate of fire * theoretical
accuracy * range * maximum speed
– Defense units value = maximum heath * shot power * rate of fire *theoretical
accuracy * range^2/2
• This is only used for comparing attack units with attack units and vice
versa .
• These equations do not take into consideration the special capabilities.
there is no rule of thumb when dealing with special capabilities. To get
proper balanced set of units can be achieved only though play testing
Production rates, unit numbers and
Lanchester’s Law
• Lanchester’s laws
– Linear Law
• In hand-to-hand combat the relative strengths of two armies
are simply proportional to their number of troop. Since only
one fighter can engage one fighter at a time.
– Square law
• Refers to the relative strengths of forces made up of units
that can aim and shoot at one another from a distance and
can concentrate their fire.
• In this case the strength of the army is square of there size.
• To avoid this make sure each player gets equal production
time
Heath, Morale, and fighter efficiency
• As with all other genres, units in war games fight at full
efficiency until their HP are gone even though that’s
obviously unrealistic.
• Making wounded or damaged units fight at reduced
efficiency introduces too powerful an effect of positive
feedback in favour of the dominate side.
• This can produce situations in which each side has harmed
the other to the point that neither is able to fight
effectively. This will cause a long boring stalemate.
• Try to avoid this situation.
• This also follows for moral.
– Moral should be avoided at all cost. If it is decided to be used it
is good to implement with special units.
Upgrades and Technology Trees
• Games with limited number of units types the
player can sometime exhaust the interesting
battle combinations to quickly.
• To resolve this problem. One should introduce
new units or to upgrade the existing ones as
the game progress.
• These upgrades might occur as a reward for
some achievement ex/checkers and chess
Researching upgrades
• The unit upgrade process is often characterized
as a form of research that the player must
initiate. This make take time and perhaps uses
some recourses.
• If there is many upgrades you make wish to
organize them into a sequence. Such that
upgrades only become available only after others
have been achieved.
• May also allow players to research upgrades at
any given time.
Single unit, unit type and global
upgrades
• You may create a number of different types of
upgrades that apply to a single unit in the
game. This will modify the capabilities of all
units of this type
– EX/ siege tank in StarCraft
Permanent and temporary upgrades
• Permanent upgrades
– This supports turn-based games that have game-time periods
that span months or years.
– This supports the players sense of progression through an
extended game
– These upgrades occur infrequently and represent a major
achievement.
• Temporary upgrades
– This supports RTS games, were you want an upgrade process
work fast enough to produce big changes in a single level but
not fast enough to care over to the next level.
– This puts more pressure on the player who has to decide quickly
whether to expend recourses on research or on building more
units
Technology Trees
• If your game has a large number of upgrades,
you should organize them into a branching
tree structure in which achieving one upgrade
makes available a choice for several others
that are logically related to the preceding one.
Technology Trees Cont.
• Designing a tech tree
– Fist think of all the upgrades that you would like to
introduce in the course of the game
– For each upgrade note if it applies to a particular
unit, all units of a particular type, all units in the
player’s forces or to the core mechanics generally.
– Note what will trigger the upgrade.
– Once you have an idea of what upgrades you want
to include you can organize them into a logical
sequence or tree.
Technology Trees Cont.
• As a general rule, upgrades should strengthen
the player’s the player’s side and give the
players new choices to make.
• Don’t worry about correctly setting the exact
cost and length required by each upgrade.
• Pick numbers that feel right.
Logistics
• Logistics- is the management of supply:
– The production
– Distribution
– Maintenance
– Replacement of personnel
– materials.
Supplies and consumable items
• Computer war games ignore the soldiers human need
– i.e soldiers don’t eat and don’t sleep
– So the game doesn’t keep track of supplies such as food or
sleeping bags.
• This is simply to much to keep track of such a nuisance.
• An exception to this is ammunition.
– In general ammunition that is cheap and low damage
should be unlimited.
– If ammunition is destructive such as nuclear weapon. Then
this should be made rare and expensive.
Supply lines
• Supply lines is the route over which fresh troops and war
material must be transported from there source to where
they are needed
• Cutting off enemy supply lines is a classic strategy of war.
• Games often model supply lines for troops only to get from
headquarters to wherever the action is.
• Few games implement supply lines for food and
ammunition for 2 reasons.
– Supplying materials is an additional task that players may not
have time to manage
– Implementing realistic supply lines means creating transport
units and modeling the supplies as individual object. This will
create a more complicated game engine and requires more cpu
time to execute.
Abstracting the distribution process
• To reduce these problems yet still require
units to create the resources that units need.
Make the production process concrete, but
abstract the distribution process
– Ex/ war craft
• This can create unrealistic strategies if not
handle carefully
– Ex/ age of empires
• Building a barracks close to enemy base and produce
troops without regard of supply lines.
Road Building
• Another way to abstract the distribution of
supplies while still requiring the player to pay
some attention to them is to let the player
build roads.
– Ex/ rise of nations
Influence Maps
• Another option is to assume that any unit within
a certain distance from a supply depot can
receive supplies from depot even though no
obstruction.
• Designers often call this influence of objects on a
terrain around them influence maps
– This is obtain by having software track regions of
influence on a map that it maintains internally
– This influence is maps include some means of
displaying the areas of influence either continuously
or at player’s option
The Game World
• The choice of setting for your strategy game is
vital.
• Dress up the underplaying gameplay in a
different setting and it can feel like a total
different game.
– Ex/ company of heroes vs. Dawn of war
The Game World Cont.
• Historical settings
– Military strategies games tend to be set in the past
ether accurately portrayed past or one in the
realms of mythology
– Games about historical events must be accurate
for the reason that the players tend to know a lot
about this time period.
– Certain amount of simplification you can get away
with as long you provide you are honest.
The Game World Cont.
• Modern Settings
– Choosing a present-day military conflict risks
generating controversy and negative public opinion
– This good gain your game some degree of notoriety.
But the disadvantages out weigh advantages.
– If you do seek to use modern settings and weaponry,
you might find less controversial to make them
fictitious.
• Ex/ red alert, modern warfare
– Battlefield scale is a problem that must be addressed.
Therefor you have to choose which scale your game is
really designed for.
The Game World Cont.
• Future (Science Fiction) settings
– Most popular and allow a lot of scope for invention.
– It is easier to base them on a successful license (star
wars, alien, Warhammer 40,000) then to carve out a
new universe.
– Must make weapons understandable to player
because these weapons do not excited in real life. It is
also good idea to indicate its power or value by some
visual sign.
– Scale is also a problem such as modern.
The Game World Cont.
• Fantasy settings
– Difference between sci-fi and fantasy is:
• Sci-fi characterize their weapons as technological while
fantasy characterize them as magical.
– This setting tend to set often in quasi-medieval
environment.
– More emphasis on close-range and hand-to-hand
combat.. Like arrows and swords
Presentation Layer
• The design of the presentation layer is critical.
Even more so in RTS games were the player is
under time pressure.
• The interface must present complicated
information in clear, well-organized ways so
that the player can grasp it easily.
Interaction model
• In strategy games, the interaction model tends
to be on a large scale.
• The player is indirectly controls the units
under his command while enjoying a god like
view of the game world.
Camera Model
• For years strategy games displayed their game
worlds in 2D, effectively treating the video
screen like a map or table top bored.
• Modern games adopted isometric perspective
in which units and buildings appear to stand
up above the surface.
• Strategy games players need to see the big
picture, the overall view of the game world.
User Interface
• Most strategy games present different kinds of
data in separate windows in much the same
manner as a windowed OS.
– Try to avoid the OS style.
– Make buttons clear, concise, and recognizable
• Remember to cater to both experienced and
inexperienced players.
– For inexperienced players need clear and easy ways to
find commands, were experienced player require
quick access, Hotkeys are good for this.
Artificial Opponents
• Game Tree Search
– Is a graph of all possible moves, that branches out at
the end of every turn.
– The artificial opponents search through the game
tree, looking for the moves that produce the most
advantageous result.
– Fewer the choices there are, the easier to design.
• Ex/ tic-tac toe vs checkers vs chess vs go
– As a designer do not expect to use this method but in
the simplest of games. The length of time for the
computer to compute a good move increases
exponentially.
Artificial Opponents Cont.
• Neural Nets
– Is a program that simulates, in the simplified form,
the behaviour of the brain cell or neurons.
– Simply a neural net mimics the brains ability to
recognize and correctly identify patterns of data.
– Future research is much needed. For know don’t
count on this for your games.
Artificial Opponents Cont.
• Hierarchical Finite State Machines
– Proven to be the most successful mechanism for creating artificially
intelligent opponents In war games. Because they can handle large
number of units and produce seemingly intelligent, coordinated
behaviour.
• hFSM contain several different FSM. The ones higher up give orders
to the lower ones.
• In video games each unit has its own FSM that determines his
behaviour. The FSM will react to changing conditions.
• hFSM allow you to design the AI from the top down, creating large
scale strategies that are made up of individual smaller scale
strategies.
• hFSM’s can be used for economic goals
– EX/workers