## 2 Materials and Methods
### Process of Creating a Virtual Reality Game
#### 2.1.3. Animation in VR Games: Techniques and Applications  
Animation in VR games is a key element contributing to the players' interactivity and visual experience. It covers various aspects, from the movement of characters and objects to the dynamic effects of the environment [37]. The main steps of animation are as follows:  
* Creation of keyframe animation: Keyframe animation is a basic technique in 3D animation where keyframes are created, and the software automatically interpolates the movements between them;
* Animation curves: These animations control the speed and smoothness of movements between keyframes. They can be used to control the acceleration and deceleration of the movement. Reshaping of animation curves is applied to achieve smoother and more natural movements;
* Test and optimization: Once the animation is created, it must be tested in a game environment and optimized for performance.  
Interpolation is a fundamental mechanism for generating the smooth and natural movements of objects and characters [42]. It is the process of calculating the intermediate values between two or more keyframes to make the motion smooth and natural. When key values are set for various parameters such as position, rotation, scale, or other attributes of a 3D model, the interpolator calculates how these values might change over time to make the transition between keyframes. In 3D games, the two types of interpolation most often used are as follows:  
* Linear interpolation provides smooth and constant motion between two frames by changing values at a constant rate. This interpolation is suitable for simple and rectilinear movements;
* Spline interpolation uses a spline cubic curve to control the smoothness and naturalness of the movement. Control points are set between keyframes to determine the motion of the object. This interpolation allows smoother and more natural movements that simulate the real world. This drives the app's camera.  
Applying Transform 3D and curves in animation helps to manipulate and manage objects in 3D space [42]. They play a key role in creating dynamic and realistic animations. The main components of Transform 3D are translation, which changes the location of the object in 3D space; rotation, in which the object rotates around a particular axis (x-horizontal, y-vertical, z-depth); and scale, which changes the size of the object about its original dimension.  
Transform 3D finds applications in motion animation and camera control. Motion animation is all about changing the position, rotation, and scale of objects in keyframes and using interpolation to smoothly transition between them. Camera control consists of animating camera movements, including position, rotation, and scale, to create different viewpoints and dynamic scene transitions.  
Morphing [42; 43] is a technique in animation that allows a smooth transformation of one form into another. It is used to create smooth transitions between different shapes of 3D objects, providing more realistic transformations. This technique is used in the current game with traditional 3D animation to control objects' movements better. Blend shapes is a specific technique in 3D animation that uses morphing to transition between pre-set shapes of the same object smoothly. Combining morphing and traditional animation techniques creates more complex and dynamic animations, which enriches the visual experience in 3D games. While animation provides the means to move objects, morphing adds smooth transformations between different object states.