Findings:
The game looks at the desirability of an object to a gnome when it picks it. For instance, it will take into consideration location, whether it's a plant, the value, and whether it is a favorite object or not.
It adds 3 if the object is outside, 3 if it is a plant, 2 if the object is worth more than $500, and it will subtract 3 for each other magic gnome that the object is a favorite of.
So for example: A stereo, worth $750, is placed outside and 4 gnomes have this as a favorite object. To calculate the desirability of this object for one of these gnomes:
1. The object is outside (+3)
2. The object is not a plant (0)
3. The object is worth more than $500 (+3)
4. Two other gnomes favorite this object (-6)
The desirability for this object is 3 + 0 + 3 - 6 = 0.
A second desirability number is considered. This is dependent on the age of the gnome - toddlers prefer Toys and Cribs, children prefer Toys and Playground Objects, Teens prefer other Teen Magic Gnomes (would appreciate another coder checking out GetTeenDesireability in Sims3.Gameplay.Objects.Environment.MagicGnome to be sure of this).
Finally, this test is performed: If the age modifier is greater than 1 AND the base modifier is exactly equal to 0, then set the base modifier to 1. Finally the two values are multiplied and presto - we have the desirability of the object.
Humanised:
Table I: Age Modifier Values | Plant | Teen Gnomes | Toys | Playground Objects | Cribs |
Toddler | 1.5 | 0 | 1.5 | 0 | 1.5 |
Child | 1.5 | 0 | 1.5 | 1.5 | 0 |
Teen | 1.5 | 1.5 | 0 | 0 | 0 |
Table II: Base Modifier ValuesOutside | Plant | Value > $500 | Penalty per Gnome with Favorite |
3 | 3 | 2 | 3 (Penalty) |
Add all applicable values in Table I and all applicable values in Table II.
If the total value of Table I is greater than 1, and the total value of Table II is 0, discard Table II's value. It is now 1.
Multiply the value of the two tables together to get the base desirability of the object.
From here it is permuted depending on the gnome.
Part II: Vampire GnomesIf you don't have one, and you have "enough [Plasma Fruit] plants", there is a 50% chance one will spawn, and it spawns at 9PM.