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Jack Leavey
Technical Designer
NEXCOM
Tech Demo
SUMMARY
I was given a random topic and 2 weeks to create a tech demo from the applicable genre. I pulled "Turn Based Tactics". As a long time player of the XCOM series, I decided to challenge myself and see if I could recreate the core gameplay loop of XCOM from scratch using Unity.
This project is a showcase of the system architecture I built in order to simulate a simple XCOM mission. The only objective is to kill all enemies.
PROJECT DETAILS
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Grid based level generation system
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Cover System
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Enemy AI with target prioritization
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Tool Development
TEAM AND TIME
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Team Size: Solo Project
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Time: 2 Weeks
GOALS
My goal for NEXCOM was to capture the basic gameplay loop you experience in an XCOM game - a turn based number crunching battle on a grid based system.
To build this experience I worked from the ground up to create a grid based tile generation system tool that allows for any size grid to be easily generated. Cover, spawn points, and enemy spawns can all be easily added to the grid with this tool as well.
Once the stage was set, the next objective was teaching the AI how to path find on the grid and use cover intelligently while still hunting down the player's characters. The enemies will prioritize offensive actions and will move towards player units, keeping in cover if possible. When attacking, enemies will consider the health and cover of all possible targets before acting - seeking to eliminate the player units in the most optimal fashion.
The Grid
The backbone of this project is the grid generation system. This is the foundation for the cover system, player movement, enemy movement, and more.
This tool allows me to quickly determine the playable field and cover locations, providing a rapid balance checking system. While it does not auto-generate the level's visuals it does allow for complete testing of the gameplay loop without the time cost of decorating a level.
Cover works in the same vein as XCOM, and is broken up into Half and Full Cover. Half cover gives a 50% penalty to incoming attacks, while full cover gives a 66% penalty. Be careful, enemies can use cover too, and will try to flank when possible!
Enemy AI
While only one enemy is present in this tech demo, the framework for additional enemy types is present for rapid production of further enemies.
The first goal of enemy development was teaching the enemy AI how to move on the grid and take the most intelligent path to reach the player's units. While some amazing AI systems like A* exist and are great for grid based movement, I decided to write my own algorithm for pathfinding.
This algorithm determines check to find the shortest path to the nearest player unit, and moves the AI to a grid spot that will put the AI's target in attack range. If multiple targets can be placed into attack range, the AI will do that instead. If the AI can also be in cover, it will prioritize getting into cover as well. If reaching a target is impossible, the AI can consider the distance remaining and will then attempt to seek cover while still making forward movement towards its target.
While simple, this series of checks and optimization of action economy makes each enemy "think" about the best possible choice before acting.
Once attacking is possible, enemies will check the odds of hitting each of the possible player units. Both the cover value and HP of the player units are considered before acting, as sometimes its worth taking a shot at an injured character in cover if that could kill the unit outright. These checks ensure that enemies always act with some level of believable intelligence - there is always a justification for why they would do what they do.
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