chaogarden.mp4
This is a recreation of the virtual pets called Chao from the 1998 Dreamcast game Sonic Adventure franchise in Unreal Engine 4.27. I started this project in early 2020, right before the COVID-19 pandemic hit.
The Sonic Adventure modding community was advanced enough in January of 2020 that it was possible to import 3D models into Blender, and subsequently export them into Autodesk FBX format. This made it easy to import the Chao models into Unreal Engine, and with some manual labor in Blender, even the blend shapes made the transition:
dark_to_hero.mp4
Animations were much more difficult to work with, as I had to find a way to piece together individual animations into whole sequences.
To that end, I wrote a Blueprint Function Library (header, implementation) which, when the user presses a button in the Unreal editor, would read a CSV file containing information about how the animations relate to each other and generate Anim Montage assets from it. These montages represent entire actions that a Chao can perform; for example, the video below shows a montage which strings together several animations to make the Chao lay down and start crawling along the ground.
chao_crawl.mp4
chaothink.mp4
Like most virtual pets, Chao have "needs" values that change over time - things like hunger, sleepiness, and boredom. When a Chao wants perform an action, it evaluates its current needs values and rolls some probability checks to determine exactly what it is going to do. I implemented this system in Unreal Engine using a Behavior Tree.
When the Tree executes a Task, the Task runs a DecideIfPerformingBehavior function to check the needs relevant to the Task and roll the necessary probability checks.
If the function returns false, then the Task yields execution back to the Tree, and the Tree continues executing the next Tasks in line. However if the function returns true, the Task enters a Tick state which performs its main logic.
The Behavior Tree Tasks for the Chao tend to be simple state machines like the one above, which represents the "yawning" action.
chaoemotions.mp4
A distinctive feature of the Chao is their Emotion Ball, which hovers over their heads. It serves to telegraph to the player how a Chao is feeling. For example, it will change to a heart icon to show that the Chao likes something, or a spiral icon if the Chao dislikes something. The video above demonstrates the Emotion Ball Blueprint that I created cycling between each of its states. The Blueprint is attached to its Chao actor, and uses a billboarded sprite to ensure that the icons always face towards the player's camera.