Monday, November 12, 2012

Negative Feedback

Nope it isn't about those comments we hear of THAT table top rpg.  The negative feedback I'll be talking about is that which takes a bit of the success in an RPG and feeds it back as a cost.  A slowing down force that curbs exponential growth.  Since negative feedback gets stronger the higher the success it can be said that it benefits the loser in the game.  This is particularly good in an RPG were you want to keep party balance.  The less powerful of the characters is less hampered by negative feedback than the more prominent, because negative feedback is a fraction of the success.  The more powerful the character, the higher the success, and the larger the feedback put back into the system.

The opposite of negative feedback is quite obviously positive feedback.  In positive feedback the bigger the success the stronger the feedback for  more success.  This  type of feedback benefits the winner, and while we all want to win, this is hardly what you'd want in an RPG.  Positive feedback is a destabilizing force that benefits the winner.  The more ahead a character is the further ahead he or she will get.  Positive feedback works against party balance.

A very simple and clear example of positive vs negative feedback in games can be seen in a deadly car race with armed vehicles.  Something similar to Death Race. In this type of game forward facing guns are negative feedback and backward facing guns are positive feedback.  With positive feedback (backward facing guns), if your ahead you can fire back at those behind you and strengthen your position.  On the other hand with negative feedback (forward facing guns) all lagging players can shoot the leading ones.  Note: this doesn't mean trailing players in party should shoot the leading ones, it's just an example of negative vs positive feedback.

Here are a few observations I'd like to point out about negative and positive feedback systems:

Negative Feedback Systems

  • Drive output towards target value.
  • Keep output within acceptable range.
  • Are stable.
Positive Feedback Systems
  • Drive output away from target value.
  • If left unchecked will drive output to infinity.
  • Are unstable.
If we take a moment to look at tabletop rpg games we can see that a great deal many have positive feedback and few have negative.  In the next article of this series I'll put up some feedback rules and look deeper into games.  Notice how some game elements build synergy and seem to take a life of their own?  That's emerging feedback and I'll touch on that on the next article as well.

Source :
Marc LeBlanc

Weapon & Damage Modelling in Era

Era uses a damage roll and soak roll for weapon and armour respectively.  The concept of damage and soak roll is not novel and has been around for a while.  Yet the mechanisms commonly in use add the die rolls to arrive at a value for damage and a value for soak.  Era on the other hand compares the rolls die to die and in doing so exploits some of the value of the roll that is lost in adding them up.

When dice are compared one to one some nice tricks can be made and some really interesting patterns emerge.  First of all lets look at an example.  Lets imagine a sword rolls 2d8 for damage and a chain mail armour rolls 2d8 for soak.  The rolls could be 6 and 4 for the sword and 5 and 4 for the armour.  Comparing the dice from highest to lowest we get:

6 vs 5 - the sword roll beats the armour roll
4 vs 4 - the sword roll ties the armour roll

Only the succeeding are added to total damage.  These rolls are called penetrating rolls.  In this case the 6 is the only penetrating roll and 6 is the total damage done.  The sword's 4 is stopped by the armours 4.  If the second armour roll had been lower, the second damage roll would have gone through and added 4 more points for a grand total of 10.

This creates an interesting dynamic because each die can represent a certain effectiveness for the weapon to penetrate the armour.  Bigger dice mean more AP (armour piercing) punch.  For example a weapon that rolls with d8 is inherently more effective against armours rolling with d6.  There is no way the armour can roll a 7 or 8 to soak the weapon's high rolls.  Adding more dice to the roll makes it more effective as well.  If the weapon has more dice than the armour there are dice the armour simply can not stop (6d4 vs 2d6, the six attacking are no match for the two defending).  Fortunately these would be the lower valued ones.  This comes in really handy when you want to simulate engulfing attacks like fire.  A blast of fire can be said to do 6d4.  All low dice, but lots of them to represent the engulfing nature of the attack.  Armour will stop the highest rolls, but be ineffective against the lower ones.

Too put this a bit more down to earth lets see how much damage a weapon of varying kind does to a 2d8 armour.  We'll graph 1d8, 2d8, 3d8, 4d8 and an amazing 5d8 weapon against the armour.

Putting it all together, calculated and graphed we get the following graph. 

Lets look at how this behaves.  The blue line shows how a 1d8 weapon fares against a 2d8 armour.  Most of the time (72%) the blade does no damage, but when it does it tends to do so at higher than normal values.  Damage above 4 and up to 8 takes up about 25% of the values.  Think of this as a dagger which is not very effective in general, but when it is it is quite good at doing damage.  It represents the ability to find critical holes in the armour quite well.

Compare this with the curve of the result when the dice are added.  Below is a graph that shows a 2d8 armour vs a 1d8 dagger (red line).  About 90% of the time the dagger does no damage and when it does it rises very gradually.

A strange behaviour happens when the armour matches the weapon (both 2d8).  Observe the red 2d8 line on the first graph.  It starts to rise quickly, then there's a small spike and then the slope diminishes.  So a quick rise to mid point value and then a slower slope toward the higher values.  Compare that to the blue 2d8 line above when dice are added.  The slope when the dice are added is very gradual and 55% of the time it causes no damage at all.

Finally when the weapon has more dice than the armour as is the case of the yellow, green and purple lines on the first graphs, there is always a minimum amount of damage done and the slope becomes more gradual.

Now lets compare the 2d8 armour against weapons with different dice (better amrour piercing properties).  On the following graph we see the armour going against d8 weapons and d10 weapons.  When facing d10 weapons the armour can't roll higher than 8 and the weapon is clearly in advantage.  Take a look at how the blue 1d10 curve behaves compared to the 1d8 curve.  It is considerably more effective against the armour.  The red 2d10 curve (on the graph below) is very close to the cyan 3d8 curve.  This is a good representation of technological advancements in weapon design.  The 2d10 could be seen as maybe lighter than the 3d8 (less dice), but it is almost as effective given its penetrating power (given the large die, d10 vs d8).  It becomes pretty easy for a game designer or game master to represent technological advantages this way.

One final graph I want to show is the effect of modifiers to the roll.  A typical example of this is magic weapons in the game.  In those cases the weapons get a plus that is added to each die rolled.  The following graph shows the d8 weapon (our dagger) against the same 2d8 armour.  Notice how the red curve of a +1 turns the simple dagger into something similar to a 1d10.  Additional modifiers create an ever increasing slope and lower odds for zero or low value damages.  Compare these two graphs with the first one at the top and compare the effects of a bonus vs adding extra dice to the roll.

As you can see by moving away from adding the dice to comparing them one on one a new way of representing the weapon's and armour's effectiveness is created.  One that gives a totally different and much more effective (greater damage) than the classic adding of the values.

A drawback is that comparing one on one may be a little more work.  But one that could be worth paying for the added benefit of the behaviour shown on the graphs and the ease in which the technological edge of a weapon or armour can be represented.

Saturday, November 10, 2012

Era Aesthetics - An Intro

Over the next few days I will be putting out a set of articles addressing aesthetics in the design of Era.  Based on Marc LeBlanc's list of 8 kinds of fun (

There are some aesthetics I'm focusing more than others. I will review them all and see if they are addressed in the design of the game and if not so why, or to what degree.

Expression is one of the key aesthetics and also the one I will touch first.  Table top rpgs have a potential like no other game.  They are not bound by the path set in a program or the graphical content of a computer game.  They are bound only  by the imagination of the GM and players.  So set them free!!!!!

I want to put just the right amount of rules to inspire and empower the players to build great settings and stories.  I strongly believe expression will help fantasy and narrative to gain more strength.  Discovery is also benefited as greater expression on the GM's part creates more things to be discovered.

But enough for now.  Until next time when I begin with expression.

Wednesday, November 07, 2012

Mage in Armor

Ok so I'm letting magic users cast spells in full plate.  There I said it.  Now fire at will!

Actually to be honest what I'm doing is not explicitly prohibiting magic users from casting in full plate, I'm just making it cost prohibitive and quite unproductive.  See with the ideas coming out of the fatigue rules it becomes very hard for a magic user to be a good magic user and cast in full plate.

Face it, high attributes are a scarce resource.  So it would be uncommon to have high intelligence, high strength and high endurance so your character can be both proficient in spell use and able to carry the burden of spell casting AND wearing full plate.

Intelligence gives you a rating of how well you can channel magical power, a term called flux (and the attribute is actually illustration, not Int).  The higher the attribute the higher the flux and the more powerful the spell caster is.  Strength allows you to carry more.  With lower strength the armor feels heavier.  On top of this endurance dictates how much fast paced activity you can do per round and as you might have guessed spell casting is one of those highly demanding activities.  So having a medium to low endurance and performing one of the most demanding activities which is spell casting, and do so inside a heavy piece of armor could be too much for the wizard.

Sure the wizard will get a spell or two out, but will be so fatigued afterwards it won't be cost effective.  If the party gets rushed the wizard might be too fatigued to effectively run away.  Overall it isn't worth the trouble to wear full plate.

Other articles to read :
Character Fatigue - A preamble
Character Fatigue - Movement & Encumbrance
Character Fatigue - Round to round fatigue

Static vs Dynamic Encumbrance

In working out the fatigue and encumbrance rules for Era I stumbled upon a limitation of the encumbrance mechanism.  At one point the encumbrance of the equipment is left behind and the effect of a sword in round to round combat is represented as a plus or minus or a cap on dexterity bonuses.  I was looking for something with less tables and less looking up.  A value I can just add up to use the same mechanism I was already using for encumbrance.

So I came up with dynamic encumbrance and tactical builds.  Dynamic encumbrance represents the load an item puts on the body when it is set in motion.  A tactical build is the sum of all combat items set in motion during an attack.  It might be simply a dagger or a sword, or armor, sword and shield.  Each item has a dynamic encumbrance and all these add up the tactical build's dynamic encumbrance.  This encumbrance can be added to the static encumbrance that is already defining base character encumbrance and through it determine the load on the character.

By using this I spare myself the trouble of having a set of extra tables to calculate bonuses and penalties based on weapon speed, dexterity and strength.  Fitting it all into a single table that's much easier to maintain.

Other articles to read :
Character Fatigue - A preamble
Character Fatigue - Movement & Encumbrance
Character Fatigue - Round to round fatigue

Tuesday, November 06, 2012

High Level Play

Yesterday Mike Mearls put out an article addressing high level play.  This is something that has concerned me since the early stages of designing Era.  In the article Mike addresses a key element which is "power" and thus the power growth that leads to it.  He puts a sentence that is crucial in showing that they're going in the right direction "To start with, we're moving away from a steady, linear progression of bonuses."  Not only does high level play depend on this, so does every other aspect of D&D play.

Historically D&D has been caught in what I like to call the battle of the curves.  Fighters move along a linear curve and magic users along an exponential one.  All types of ideas have been put forward to try to "curve the curves" and make the straight line a curve or iron out the curved exponential one into a nice straight line.  Seeing the futility of this exercise I decided to start from scratch an place a self regulating power measurement called XP Tax.  Simply put XP Tax represents the cost of current skill and power upkeep.  The more power you have the more you have to pay for upkeep.  On the other hand the more power you have the easier it is to obtain that upkeep.  So from the character's point of view it doesn't feel like an impossible hill to climb.  The character sees it as a constant challenge rather than one that grows exponentially (A bit of tongue in cheek, those doing the math will notice hardship as XP Tax reaches 100%, but in daily gaming the statement holds).

The usage of XP Tax gives power a different curve to grow on and allows the player to retrain.  Since XP Tax is a percent of your XP income it can never exceed 100%.  When you reach 100% your character can no longer grow, it costs so much to upkeep that there is nothing left for the character to acquire new skills and powers with.  This forces the player to play in a way that isn't always "more more more".  The character can forfeit some skills by not paying their upkeep cost and make room for others.  The player can keep playing by modifying the character to the new arising needs of the high level campaign.  By leaving behind the skills that got the character to these levels and obtaining new skills that are more fitting for these higher levels the player can continue play, but do so without a character that is overly powerful and prone to unbalance the game.

The following graph shows four types of growth; exponential and linear in blue and red respectively.  They are the classic magic user vs fighter curves.  When a cost for the current skills are added the curves begin to flatten out or become asymptotic ("a line such that the distance between the curve and the line approaches zero as they tend to infinity").  While the logarithmic (log) curve isn't truly asymptotic it is so for practical game purposes (you're not going to reach level 1000).  Yet when you put a percentage cost to XP then it truly becomes asymptotic and behaves like the green line.  The character will never be able to reach beyond a certain level (100 % XP cost).  That effectively caps game power, but added to retraining rules it simply promotes the game in a different direction.