.com.unity Forums - Suggestion for an improved plague model.

Complexity is nice, but you really probably want a system that players can grok quickly and easily while still leaving many paths available. Not saying this system meets those requirements, but I think it does a fair job. Here we go...

Each planet has a plague level, ranging from zero to five, with zero being the same as no major plague. In addition, they also contain an infected percentage from 0 to 100%. The effects of a plague are as follows:

10% reduction of all production per plague level times the percent infected.
10% reduction of all construction rates per level times percent infected.
10% reduction of reproduction per level times the percent infected.
Minus the plague level squared, times the percent infected from happiness (e.g., -25% * percent infected for level 5 plagues).
Population times percent infected times 1% per plague level equals the maximum deaths per turn. Make one random "roll" of 0-max for each plague level. Take the highest roll.
Each turn, increase the infected percentage by a random -5% up to the plague level times 5%. Multiply this value by the race's Tolerance attribute (positive Tolerance bonuses reducing positive growth and increasing negative growth, and vice versa).

Note that all these percent changes to things such as reproduction are multipliers to those values, not subtractions. So a level five plague cuts your production in half, it does not reduce your construction mutliplier by 50% like many other modifiers in the game. This is especially important to note on the change in infected percentage. So with a 50% infected percentage and +10% change, you get 55% not 60%.

Weapon platforms and troops on a plagued planet suffer penalties to both attack and defend equal to 5% per plague level times one-half the percent infected. Unlike above, these are straight subtractions, so -25% for a level five plague to a 40% to hit chance means it becomes 15%.

Like planets, ships can contain plagues too. They do not, however, have an infected percentage.

Any ship with a medical bay is immune to all plagues of a level lower than the medical bay. (Assuming Full Coverage, see below)
Plagues of a higher level have a 5% chance, minus one for each level the plague exceeds the medical bay's level, of having their level reduced by one each turn. Note that reducing a plague to a level below the medical bay instantly cures it. (Assuming Full Coverage, see below)
Ships suffering from a plague suffer the same combat penalties as weapon platforms and troops on infected planets unless they use a master computer.

As a side note, troops cannot, by themselves, be infected. If the planet they are on is, they are. If the ship they are on is, they are. Otherwise, they are not. Note also that while ships with a master computer can be plagued even though they do not suffer combat penalties for being so.

Medical Bays cover a certain size in Kt. Value2 of the medical bay ability is used to indicate how much coverage they provide. A fully covered ship is one who has the sum of their medical bays equal to or greater than the ship's size. When different levels of medical bays are mixed, all bays below the strongest medical bay have their coverage values multipled by their own level and then divided by the level of the best bay. So a 200 Kt level 5 bay and a 200 Kt level 2 bay cover 280 Kt at level 5 (200 * 2 / 5 = 80, plus the 200 from the other bay).

If a ship has only partial coverage, they do not gain total immunity. Instead, the percentage of size actually covered is the percent chance per turn they medical bay is actually allowed to function. However, unlike with full coverage, plagues below the level of the medical bay are not removed if they bay works on a given turn. Instead, they have their level reduced by one automatically.

How do ships get infected you ask? Any of the following transmits a plague of an equal level as the source to the ship:

They pick up or deliver any cargo to/from an infected planet. Releasing cargo into orbit, such as mines, does not count.
If they successfully board, or are boarded by, a plagued ship they recieve the same plague level.
They recieve supplies from a resupply depo on a plagued planet.
They are fleeted with a plagued ship. (See below)
They have components repaired by a plagued ship or planet.
They are retrofitted by a plagued source.
They are built by a plagued source.
A mothballed ship is unmothballed by a plagued source. Mothballing a ship removes its plague.
The ship receives experience via a training facility in a plagued location.

To prevent plagues from spreading insanely, I'd add the ability to Quarantine a planet, ship or fleet. If the quarantined object does not have the plague, they will not engage in any activity with a plagued source that will give them the plague. If the object is already plagued, it will not engage in any activity that will allow unplagued objects to contract the plague. And no, quarantining a plagued ship won't protect it from being boarded by an unplagued ship http://forum.shrapnelgames.com/images/icons/icon7.gif . Special exception for those who thought there was a hole.

In addition, a fleet is treated as if it is a single ship with a single plague. This means all medical bays within the fleet are combined to determine if they provide full coverage for the entire fleet. Removing the plague in the fleet works the same as if it were one gaint ship.

Next, how to cure planets. Make a medical bay component for weapon platforms that leaves no room for weapons. It works under exactly the same rules as medical bays for ships, except their value2 indicates population protected. So drop a bunch of "Emergency Hospitals" on a plagued planet and they can whip the plague eventually. It would also be possible to make a troop sized Version of the component.

Now how to deliver plagues to planets. First, a planet that conducts an activity with a plagued ship,which would plague a ship (such as resupplying a ship) recieves a plague of that level at an infected percentage of 1% or 1 divided by their population times 10%, whichever is greater (so on a planet with 5M pop, they'd get 1 / 5 * 10% = 2%). This is a once per turn event, no matter how many ships are involved, although the greatest plague wins, so you can't plague a planet with a level one, then quickly drop the cargo of the ship with the level five plague. As a special case, if the planet's infected percentage is already greater than the initial exposure percentage, then contact with a greater level plague increases the planet's plague level by one (and leaves the infected percentage alone). This can occur at most once per turn to a given planet.

Weapons use their damage rating to determine that number being divided by. At the end of combat, total up that number from all plague weapons (assume for the moment they were all the same level) and divide by the population and multiply by 10% to find the infected percentage of the planet after combat ends. If multiple plague level weapons are used, the greatest plague level wins. All lesser weapons contribute to the total modified by the weaker weapon's level divided by the greater weapon's level. So, if a plague level five weapon hits for 50, then a plague level three hits for 50, the total number so far becomes 80 (3 / 5 * 50 = 30, plus the 50 from the first weapon). On a planet with 2000M people, just those two hits would yield a level five plague with an infection percentage of 0.4% (80 / 2000 * 10%), which you could use a quick random roll to determine how to round: Using a "d10", on a 1-4 round up, on a 6-10 round down.

Make a few of those values moddable and make fighters carry the combat penalties of the plague from their launch source and I think that about covers it. You get medical ships with tons of medical bays to fleet with infected ships and/or accompany your regular fleets. You can load them up with cargo bays to carry portable hospitals for cleaning up your planets.

See, lots of possiblities and its all short and sweet http://forum.shrapnelgames.com/images/icons/icon12.gif . Oh, I dropped a section on spreading plagues between planets in the same system just via the invisible trade that occurs because it was getting kinda long, but it would just be an extension of the infected ships infecting a planet, just using an invisible plagued ship instead.