Game Design Document
This document outlines the design goals, philosophies and core gameplay mechanics in Team Purple's Populous 2. It also serves as the go-to place for definitions for terminology used throughout the planning documentation, as well as an easy reference for the critical features required for the product.
The primary focus of this project is to build a scalable and customisable engine for recreating "god games" such as Populous 2: Trials of the Olympian Gods (1991) developed by Bullfrog Productions and published by Electronic Arts. While gameplay elements certainly are important, the ability to switch out assets and easily edit said elements without changing the underlying code takes precedence.
Populous II: Trials of the Olympian Gods, like its predecessor, is a God Game where the demigod player must guide their people in one battle after another against an opposing Greek deity with followers of their own. Both the player and opponent have very little control over their people, with the focus instead being on the abilities they can use to influence the tide of battle. Examples include pillars of fire, storms and deadly fungus. The aim of the game is to destroy all of your enemies' units in a timely manner as possible, in order to prove yourself to Zeus and gain a place in the Pantheon.
As previously alluded to, Team Purple's Populous 2 will likely not be as feature-rich as the original. The 1000 levels, myriad of abilities and a large variety of buildings, heroes and wandering monsters are not a priority. Instead, Team Purple instead aims to create a solid foundation of the gameplay mechanics and allow the addition of more through a structured codebase, as well as the easy customisation of existing features through designer tools such as a level editor, exposed creature stat files and easy asset switching.
The key features of Populous 2 that we would like to replicate include a large number of wandering NPCs and their interactions with each other (such as merging together to form a more powerful unit and fighting with enemies), a selection of abilities that the player can use to interact with the game world (most notably Populous 2's iconic raise and lower ground mechanic) and some form of easily customisable AI opponent.
Team Purple also aims to preserve the original game's 'bumbling' nature of the NPCs. In Populous 2 the player had little control over the precise actions of their people, so acting off the random actions of the troops was a key feature that made the game dynamic and replayable.
Team Purple aims to implement these base features to create a minimum viable product, but create underlying systems to write code in such a way that customising and building upon the project is easy.
Just like in the original Populous 2, the player's aim is to destroy all of the enemy units by both building up and supporting their own forces, as well as hindering the enemy troops via the use of spells and promotion of the friendly population.
"The Ultimate Goal - Defeat Zeus" - Populous II: Trials of the Olympian Gods Manual
In the original game, the added challenge of defeating the enemy efficiently was also present as depending on how well the player completed the level affected how far they would progress. In Team Purple's version this extra mechanic will likely not be present as just one randomly created level will be used to demo the game mechanics, the player will simply aim to defeat their opponent using all of the abilities at their disposal.
The primary skills the player needs to possess to be successful in Team Purple's Populous 2 are good observation and management abilities. The player must keep track of both friendly and enemy units and react based on their actions, manage the sprogging (creation of) friendly troops, as well as handling their mana in order to use spells and hinder the enemy.
The game's target market is not children, so the intricacies of management do not have to be toned down for the sake of simplicity and the idea of multi-tasking being pivotal for success in Populous 2 can be promoted.
Before units, heroes and settling are discussed the energy mechanic needs to be explained as it is an integral part of the game. All units and buildings have an energy value which decreases over time. If the value reaches zero, the unit dies or the building is destroyed. The energy value is used for resolving conflicts, sprogging new units, and more.
Units and the interactions between them make up the fundamental mechanics in Team Purple's Populous 2. By default, units will simply walk around the map randomly - the player has very little control, outside the use of the Papal Magnet (discussed later), over their pathing.
Units also have the ability to fight and merge with other units. If two units of opposite teams wander into each other, then they immediately enter combat. The result of the duel is decided by how much energy the units have - the one with more energy will be victorious. However, the winner's energy also decreases by the amount of energy that the loser possesses.
Merging works in a similar way. If two units of the same team collide with each other, then they immediately merge into a more powerful unit. Energy again is the key factor, as the new unit will have the combined energy of the two which created it.
Continuing from merging, the most powerful form of units in the game are Heroes. Heroes are created by using a spell when a player has sufficient mana. Heroes are strongly powered characters and take a large sum of mana to summon. There are 6 heroes, one from each category of effects. When a hero spell is used the player's leader will transform into a hero from the selected spell category. Heroes also tend to be immune to the effects of powers from their own category.
A standout feature of Heroes that contrasts all other units is that they do not lose energy over time. Therefore it is often in the player's interest to dedicate resources to creating a Hero as they are not only more powerful but more sustainable as well.
The population of a player’s god is a strong metric for success in Team Purple’s Populous. Each unit contributes toward the player’s mana pool which in turn increases how often a player can use their abilities against their opponent. However, the player would not be able to measure their entire population easily so a colosseum is used to view their population against the enemy’s.
The colosseum fills to represent the total population of a player and can be seen as an indication of which user is winning.
Units also possess the ability to settle and create buildings. Again energy has an impact, as the amount of energy a unit has affects the quality of the building they produce.
Settling provides the ability to increase the population of a player's units. Over time more units will create more settlements causing an exponential increase in population towards filling the colosseum.
The key mechanic of buildings is their ability to create new units. Over time a flag will be raised above the building and once it's at its full height the player is able to check on the building to sprog a new troop. This sprogging will decrease the building's energy by the amount of the newly created unit.
In Team Purple's Populous 2 the player will have access to a number of abilities to turn the tide of the battle. The core of the ability system is mana, the resource used to cast the spells, and managing its level will be another key responsibility of the player.
There are 6 categories of powers in Populous II: earth, water, wind, fire, plants and people. The original game features 30 powers overall. These powers cost the player's mana to perform. Great effects like tidal waves and earthquakes cost more mana as they are more devastating, whereas a much lesser effect like raising and lowering land costs a much smaller amount of mana. When using their powers the player must consider the cost-effectiveness in each case. This allows the player to save more mana for more devastating effects against greater foes the enemy player may use.
A frequently used spell in Populous II is the papal magnet. This allows the player to dictate a position for all their units to congregate at. The first unit to encounter the papal magnet becomes the leader unit for that player. When this unit dies the papal magnet is left at its death location and resumes its effect of pathing all of a certain team's units to itself.
While the original Populous 2 featured wandering monsters that left trails of destruction in their wake, this addition is not a priority for Team Purple. Fleshed out and functional units will suffice for the demo, and due to the modular design structure of the code at a later date monsters could easily be added.
The level in Team Purple's Populous 2 will be randomly generated to provide a unique experience to the player every time. A key feature of Populous 2 was its variance in terrain height and the control the player had over it. Team Purple looks to mirror this both in the initial creation of the map as well as in the game itself through the raise-lower ground spell.
Changing terrain height is crucial to allowing a user's AI to settle. This can create impassable obstacles or in further implementation of a settle system prevent large structures from being formed without a uniform surrounding height of the terrain.
Raising ground in Team Purples implementation uses recursion to cause a cascading effect on surrounding tiles. This is also an effect in Populous II, where a user would keep incrementing a tile’s height, a peak would be formed with surrounding tiles causing a slope somewhat to make a mountain or hill like structure.
Team Purple aimed to implement a solid and customisable enemy opponent, with a stretch goal being a friendly AI helper as well. The implementation has succeeded at allowing for the creation of a highly customisable enemy opponent that uses the same abilities a player would with scalable accuracy at the time of it's creation.
The AI has also been split into second major part, and that is the sprogging AI, which is also present as a friendly AI helper, just like in the original game. Instead of having the player manually go around their own territory all the time and sprogging every settlement, the AI helper goes around and sprogs the houses for them, as well as the enemy opponent. The AI for the different teams supports having different styles and it can be a highly accurate system, only sprogging at maximum energy, as well as an imperfect chance based AI, linearly scaling with the settlement's energy.
These systems allow for setting up a dynamic difficulty between the levels through making enemy AIs more advanced, while the player's AI helper worse. It also allows for the creation of thematic AIs such as one that only uses fire abilities.
There is no progression as such in Team Purple's Populous 2. With just one randomly generated level, the focus is on creating a solid base to build upon rather than focusing on replay value at this early stage.
However, the enemy AI will be able to be customised to alter the difficulty and due to the random nature of the NPCs the game will be different every time the player plays.
The player wins the game by destroying all of the enemy's units. Upon winning, they will be offered the chance to replay the game on a harder difficulty.
The player will lose the game if their entire population is wiped out, either through the direct result of the enemy's actions or by simple chance of the NPCs interacting with each other.
If the player loses they will be offered the chance to replay and give the game another try. Due to the random nature of the NPCs and enemy AI, the experience will not be exactly identical, however, the values dictating the enemy AI's behaviour will stay the same allowing the player to try again at the same difficulty level.
Team Purple's Populous 2 has an isometric perspective, aiming to mirror the original. The precise beauty and fidelity of assets will likely be sacrificed to allow for faster production and easy identification of game elements, however, the ability for said assets to be simply swapped out will nullify this problem for a release version of the project.
Visual elements can be readily changed by changing the resource the load handler is calling. This system can be used to change biomes and the overall appearance of the game. Populous II benefited from this for its DLC where a user could change their game theme to a different era.
A pixel art style will be used and basic animations will add to the effect.
As for UI, Team Purple will take inspiration from but not exactly mirror the original game. The assets used are to illustrate the terrain editing abilities and differing heights of terrain as well as demonstrate a functional pathfinding system. The intention of the assets is to have all underlying systems and components that are used by other components be represented appropriately and available for a graphic designer to later change the assets to appear as they would need for their project.
The original game only utilised a small number of sound effects as part of a very basic audio system. The audio effects we use are not considered over the functionality of our audio system. The intention is to have an effective audio system where the capability lies for a sound designer to later employ better sound effects and design utilising our system.
Team Purple aims to produce both a PC and Arcade machine build of the game.
The Team Purple PC build of Populous II uses mostly mouse controls. This mimics the original game and others of the RTS genre. UI on-screen is interactable by using a cursor.
Mouse 1: Select Spell / Use Spell / Use UI
Mouse 2: Alternate Spell Use
Arcade machine control: As the arcade machine has a special set of peripherals (Joystick and buttons) it requires a separate input handling system. The target machine runs on Windows, and all the available inputs are mapped to buttons on a standard keyboard, this input handler will need to mimic keyboard button presses. Also important to note, that as the mouse input is planned to move a cursor object on-screen taking the x and y-axis delta at each frame, the ideal cursor controls on the arcade machine can leverage this solution by moving the same cursor by a set amount each frame. This way we can ensure 100% compatibility between the two control systems.
Populous II: Trials of the Olympian Gods. (2022) wikipedia [online]. 25 February. Available from: https://en.wikipedia.org/wiki/Populous_II:_Trials_of_the_Olympian_Gods [Accessed 13 March 2022].
Populous 2. Old Games. Available from: https://www.old-games.com/download/5482/populous-2 [Accessed 13 March 2022].