Wednesday, August 29, 2012

Bell percentile app

Mmmm... Game design maths. Probabilities and chi and all that jazz. I have to say I hate discussing it- it sucks the fun feeling out of the game development process, but its something you have to face.
I picked up a dungeon magazine at a boot sale a few days ago and it actually had a program in BASIC you could type in to your 8bit computers to work out if your favorite dnd dice is biased. Yep, seriously.
Personally I like to grab a handful of d10 that are identical and pick ones out at random, but other players swear by various practices such as keeping their dice only in their lucky velvet bag or rolling left handed with their eyes shut etc.
Works for me.
My friend John B says he is the worst dice roller in rpg history, and he appears to be right by the games we play. The other players started edging their dice away from him like he was a vegas cooler. He rolled a natural 20 in dnd once and had to use all his strength of will not to jump up and run around the room trampling all the prepainted plastics.

Anyway, percentile dice, like d20's have a probability issue. They are linear. Rolls have just the same chance of rolling 1 as rolling 100 or rolling 50.
Ideally (velvet and lucky left hand modifier excluded of course), when measuring a characters performance you want a bell curve. That is, your most likely to get a middling result and least likely to score an extreme.

One thing I have been thinking of doing for a while for my homebrew games is a percentile dice app that Dundred that generates bell curve results for percentile dice.

If you roll 3D100 and divide the result by 3, you get a bell curve, but of course, you would not want to do that in your head for fun (if you do, go seek help) but as an app its great to have as an option.

Another way to skew d100 is to have the player roll 2d10 and pick which one is the tens unit based on if it is a high result or a low result.
If you do this, players score hits more often, but it does not effect double digit rolls. It does make 10 no better than 9, so you get a slight blip in progression- much like shadowruns exploding dice on a six ultimately mean its as easy to cast a seventh level spell as a sixth but hey, no biggie for a maths free dice bias.
Its actually quite similar to dndnext's proposed 2d20 advantage system in some ways. If you have the advantage, you pick lowest digit d10 to represent your tens, if disadvantaged, you pick the highest.
Until I build a model on the pc and test that it could live as an optional rule. Currently advantages give you higher odds of hitting by adding to the target number.

However, the doubles as critical successes achieves a performance result of 10% strong, 88% average and 2 % as close shave (exact roll and roll of 100). So whilst not being a bell curve in terms of odds, the quality of the roll will be average most of the time.

Scaling coins.

Originally I had planned on using the pricing for items from Retro clones to make dundred compatible with old adventures, but an idea struck me that may be too nifty to ignore.

If 10 copper pieces bought you 1 silver, and 10 silver bought 1 gold, a 10 gold bought you a Platinum piece, you get a nice effect for pricing items by quality.

C= crappy
S= standard
G= good

Note the first letter is the same as the coin- Copper buys crappy, silver buys standard, gold is good, platinum is premium.

If I price items in generic coins, the type of coin you spend gets you a different quality item.
Say a hand weapon costs 50 coins.
50cp gets you a crappy sword +5
500cp (50sp) gets you a standard sword +10 to hit.
5,000cp (50gp) gets you a good sword +20 to hit.
50,000cp (50pp) gets you a premium one. +30 to hit.

This scale is more in my imagining of a fantasy middle ages too- where folk would have only a few, big clumsily minted coins (and probably a rusk of stale bread) in a pouch.

A single copper can buy your adventurer a crappy drink at the crappy tavern. Three coins and you have a meal. 12 and you have a days provisions (3 drink, 3 food).
The 10x10x10x10 means as treasure accumulates tenfold, players could have upgraded all their starting items one quality level.
Quick, easy and only 1 price list governing 4 standards, and having a built in advancement curve.
Plus, just write everything down in cp, and the digits will tell you how many gold, silver and platinum you have....
2314c is 2plat, 3gold, 1silver and fourpence.

Monday, August 27, 2012

Quick qualities

Quality on a roll under system can be done a lot of ways. The obvious is to deduct the lower of the roll and the target.
Need 15? Roll a 9. Won by 6.
Need a 32? Roll a 51. Win by 19.
But this is a maths step, the less of these the better in my opinion.

Another method is to just take the tens into account. Need 63, rolled a 32- 6-3=3, or 30 if your talking in tens.
This is a much easier on the fly calculation, but there are a couple of other options.

On a success, you get the face value of the dice. Lets say you have 45% to hit. Rolling 00 to 45 on the dice gives you the same range as 45-result. It is instant.
But of course it only works on successes.
For fails, the face value system can work using this trick since only the DM needs judge a fail. Get the player to announce the face value, then take the tens digit from ten. "64- fail." would be (10-6=4) or fail by 40.
This takes all maths out for the player, they just roll and announce the face value and if it is a hit or not.

I personally feel a 1-10 scale for quality or 'Marks Out of Ten' is more practical than a 1-100 scale, as its hard to visualize such granularity.

However, the double digit system (11,22,33,44,55 etc) also gives an equally easy to visualize quality.
Exact pass. Pass. Double pass.
Fail by 1. Fail. Double fail. Natural 100.

Ep. Close shave.
P. Sound hit.
Dp. Great hit.
F1. Close (but no cigar)
F. Minor failure.
DF. Bad failure.
100. Critical fail.

If you only need quality for damage, that only happens on a hit. Thus face value of tens digit is perfect- so long as zero counts as 1 hit or has a positive result of some form.

Percentiles & polyhedrons

Ooh those pretty dice. How exotic where they?
It seems a shame not to use all the funny shaped dice, but for the core mechanics at least I am a big fan of percentile dice. Rest assured I will find something for those polyhedral pretties to do, but for now let me extol you with the virtues of the d100.

First up it's old school! DnD originator Dave Arneson also favored the d100 in his co-authored sequel to DnD, Adventures in Fantasy.
My departure is going with a roll under system for tests. With a roll- under system, calculating odds is a no-brainer. I am all for no brainers me being somewhat dim witted myself. If the DM says you have a 20 percent chance of making a leap, its easy to visualize the risk your taking.
Roll under is my favored method as gives instant results. Need 8 or less to hit? Rolled a..... 02! (cheers!)
Rather than a... rolled a 18, plus five, plus uh... Two, minus one... 24. Did I hit? Dm:yes (cheers!)
You get a good suspense/payoff with roll under.
For D'hundred Rolling equal or under the odds given by the DM is a hit. Over is a fail.
To add a little granularity, if you roll double digits, the result is a double fail or double success (aka major fail/success).
This gives 10% of fails and successes as doubles. Therefore, the higher the odds of success the more likely of getting a double success, the less likely a double fail.
I think rolling a natural 00+0 ('undred) may give you a critical success, and 99 a critical fail.
Minor fails result usually in the DM putting the character to a worse position than before.
Jump for a ledge? Fail? You catch the ledge by your hand. Fail again? You slip to your fingertips. Another? Bye, bye!

Lets look at quality next...

Welcome to zero hp

Welcome indeed! In this blog I will be discussing all things dungeony and rather dragony, as I develop my home brew RPG rules into a released system.
Now before I begin, this is not a retroclone or OGL project. It is not Dungeons and Dragons and does not make any claim to be. Rather, it is a response to DnD, much the same as Tunnels & Trolls was.
I hope to capture the spirit of old school gaming, but with a system that is developed from the ground up with the benefit of decades of hindsight.
I invite you to join me, discussing the pros and cons of various game mechanics and sharing your experiences, as I build this new game.

This is gonna be fun!