Update vs FixedUpdate

In Unity, both Update and FixedUpdate functions are used to update the behavior of objects in a scene, and while they serve similar purposes, there are key differences between the two.

'Update'

The 'Update' function is called once per frame and is ideal for handling input, updating object positions, and performing most general-purpose tasks. It is not frame-rate dependent, meaning it can vary in execution time depending on the performance.

void Update()
{
    // Input handling
    float horizontalInput = Input.GetAxis("Horizontal");
    float verticalInput = Input.GetAxis("Vertical");
    
    // Movement
    Vector3 movement = new Vector3(horizontalInput, 0, verticalInput);
    transform.Translate(movement * speed * Time.deltaTime);
    
    // General-purpose tasks
    // ...
}

In the example above, we retrieve input from the horizontal and vertical axes and use it to control the object's movement. The method 'Translate' is used to move the object in the specified direction at a constant speed. General-purpose tasks can also be performed within the function 'Update'.

'FixedUpdate'

The function 'FixedUpdate' is called at fixed time intervals, making it suitable for handling physics-related calculations. It is frame-rate independent, ensuring consistent behavior across different devices and frame rates.

void FixedUpdate()
{
    // Physics calculations
    rb.AddForce(transform.forward * forceMagnitude);
    
    // Other physics-related tasks
    // ...
}

In the example above, we apply a constant force to a Rigidbody component in the object's forward direction. The use of 'FixedUpdate' ensures that the physics calculations occur at a fixed rate, regardless of the frame rate. This is important for maintaining stable physics simulation.

'Update' vs 'FixedUpdate'

Key differences between the functions 'Update' and 'FixedUpdate':

• 'Update' is called once per frame, while FixedUpdate is called at fixed time intervals.
• 'Update' is frame-rate dependent, while FixedUpdate is frame-rate independent.
• 'Update' is suitable for most general-purpose tasks, including input handling, object movement, and non-physics-related operations.
• FixedUpdate is specifically designed for physics-related calculations, such as applying forces, adjusting Rigidbody properties, and performing other physics-based operations.

Conclusion

It's important to note that 'Update' and 'FixedUpdate' can coexist in the same script, allowing to separate physics-related code from other general-purpose code. Understanding the differences and using the appropriate function in each context helps ensure smooth and consistent behavior in the Unity projects.