Strategy GamesBy 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

– Unit uses pathfinding AI to find its way there, taking the quickest route while avoiding obstructions• Attack

– Unit advances until the enemy units is in range. Then open fire, and pursues if enemy retreats.• Stop

– This order countermands both attack and movement orders.• Hold

– This command tells units to attack any enemy that comes into range, but don’t purse it if retreats.• Establish Formation

– Sets formation of troops for tactical purposes.• Produce

– used to produce new units by consuming recourses.• Retreat

– Units will move to safety that leaves the unit more vulnerable while moving but units move faster.• Dash

– 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 MechanicsDesigning 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

• 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

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:– 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