grnt426 / pokeserversim

Simulating a world of Mons!

PokeServerSim

Out of curiosity, I wanted to explore what it might be like to create a mostly-stateless procedurally generated world for spawning Pokemon.

The Player features are as follows:

1. Players should feel like Pokemon are generated randomly as they move about the world.
2. Players expect to see a distribution of Pokemon rarity (Common -> Rare).
3. Players should see region relevant Pokemon.
4. Players should see the Pokemon others see, as to encourage teamwork and discovery.

The Technical constraints (for fun) are as follows:

1. Regions not seen should not have (substantial) calculations performed
2. Generating Pokemon should be stateless. No information about previous spawns/timers are needed.
3. Caching results of generated Pokemon is OK

Currently

Basic simulation is in place, with "Players" moving around and triggering generation lookups. As player's see Pokemon, they are added to the player. Generation lookups are stateless, and only require the player's position and the server's current time to make a decision to generate a Pokemon or not.

Example Output:

Found one! 217 367
Found one! 0 796
Found one! 21 20
Found one! 263 336
Found one! 757 594
Found one! 753 605
Found one! 796 15
Found one! 754 598
Found one! 744 619
Found one! 757 0
Player -2818048 caught 1
4 LEAFMON captured.
Player -16774693 caught 1
2 FIREMON captured.
Player -13703129 caught 3
1 WATERMON captured.
1 FIREMON captured.
2 LEAFMON captured.

As shown above, player's capture differing amounts and kinds of Pokemon, despite a fixed distribution for spawning.

Interesting Bits

Visualizing the Algorithm

The most interesting part is in Generator.generate(...). This function is the entire algorithm for deciding to generate a Pokemon or not.

I enjoyed trying to visualize how this would look, and I came up with a rough approximation:

Imagine that each point in space is represented with a stick, and along the stick are tick marks equally spaced, by an amount of interval. As time moves along this stick, a Pokemon is generated whenever we pass a tick mark. Given no other inputs, its trivial to see that every point in space would generate the same Pokemon, at the same time, in an obvious pattern (defined by the interval length). To "start" at different positions along the stick, we hash both the position and time. This ensures that as a player moves, they don't see the distribution from a statically defined world. It "appears" that Pokemon are generated randomly along their journey.

This still suffers from an obvious flaw: A player sitting in one location will see the distribution, and it won't appear random. For this, we have other solutions that will mitigate it further.

Controllable Variables

To combat this, we have several controllable levers: sight radius, location fidelity, and interval periodicity.

Sight Radius affects the number of points we look at for determining if a Pokemon should spawn there. A sight-radius of "one" means our current coordinate. Increasing the sight radius necessarily increases the number of Pokemon seen

Location Fidelity determines the density of points to consider for a given player. Increasing the density will mean more points to look up for a given sight radius, and will increase the spawn rate.

Interval Periodicity determines how often we hit a tick mark over time. Decreasing this value will increase the spawn rate.

Interval Length determines how long a Pokemon will remain seeable by other players, and how long a player has to react before it disappears. Increasing this value draws more players to a given area, and will increase the average number of Pokemon available at any given point.

And many more.