Euphoria Engine is a game animation system suite from NaturalMotion that is used by Rockstar Games in their games to enhance the physics-based reactions of both humans and animals. It combines physics and collision simulation, artificial intelligence, and hand-made animations to create believable behavior and reactions from game characters. Rockstar Games had used this engine in their past games but they claim that the engine has especially evolved in Red Dead Redemption 2.
This is very noticeable in the behavior of horses in Red Dead Redemption 2. They react to gunfire and predators like a real normal animal would, and Arthur has to calm his horse down to avoid being buckled or trampled. If the horse is shot or bumps on a tree or rock, there are a range of realistic outcomes like rolling off the horse, being dragged, or even being trapped under the horse in which you have to fight to get free.
The animation effects of Euphoria have been implemented too in animal and human collisions, bullet collision animations, transport like rowing canoes and boats on the river, as well as bushes and trees. All things have a real sense of weight, and don't just throw out in the air like ragdolls like in other games.
There are a wide range of reactions in humans as well if they're injured. If you try to use a lasso to an enemy for example, they will sometimes try and reach for the rope or fire off some shots in the struggle to get free. Enemies grip their wounded areas, respond to bullet barrage by flinching, ducking, and looking for cover to reload, and even try flanking and surrounding the building where Arthur is for a coordinated attack.
Other games in which Rockstar Games used Euphoria engine are:
- Grand Theft Auto IV
- Max Payne 3
- Red Dead Redemption
- Grand Theft Auto V