Beyond Fixed Timesteps: A Smoother Path to Game Development

Is the fixed timestep a performance bottleneck in disguise? It’s time to rethink this sacred cow of game development. The heartbeat of any game lies within its game loop, the continuous cycle that updates game states and renders visuals. The “fixed timestep” approach is often treated as gospel, an unbreakable rule for consistent gameplay. But what if I told you that’s not always true?

The Fixed Timestep Fallacy

The core idea behind a fixed timestep is simple: update the game logic at a constant rate, regardless of the actual frame rate. This is achieved by running the update logic multiple times per frame if the frame rate is too slow, or by skipping updates if the frame rate is too fast. While this offers the illusion of determinism, it comes with real drawbacks.

The Jitterbug: “Jank” at Non-Target Framerates

When the game’s frame rate dips below the target update rate, the game loop struggles, leading to noticeable “jank” or stuttering. The game is forced to drop frames, creating a jerky, unsmooth experience.

Wasted Potential: CPU Cycles Gone Astray

Conversely, when the frame rate exceeds the target, the CPU burns cycles on redundant updates. These wasted cycles could be used for detailed graphics or complex AI. Consider exploring "Technical Art Strategies for AI-Assisted Game Development" to see how variable timesteps could enhance AI driven content.

Physics Headaches: A Tangled Web

Fixed timesteps complicate physics simulations. Maintaining consistent physics across different hardware and frame rates becomes a balancing act, often requiring compromises.

Embracing the Variable: The Benefits of Flexibility

Variable timesteps embrace the fluidity of frame rates. Instead of forcing a fixed update rate, the game logic is updated based on the actual time elapsed since the last frame. While the examples here use Unity, the core concepts of variable timesteps apply to other engines like Unreal Engine, Godot, and custom game engines.

Smooth Operator: Gameplay That Glides

Variable timesteps: the path to consistently smooth gameplay and improved game performance. The game dynamically adapts to the available processing power, providing a seamless experience.

Resourceful Efficiency: Making the Most of Your Machine

Variable timesteps allow for more efficient resource utilization. The CPU only performs updates when necessary, freeing up resources and improving overall performance. Variable timesteps can indirectly alleviate other common performance bottlenecks (draw calls, overdraw, physics complexity) by freeing up CPU resources, allowing for more efficient distribution of processing power.

Content That Scales: A Future-Proof Approach

Scaling content across different hardware becomes simpler. Animations, particle effects, and other time-based elements adapt automatically to the frame rate, ensuring a consistent look and feel. Variable timesteps can significantly improve environmental animations and effects, especially on lower-end hardware, allowing for richer, more detailed game worlds. Check out "Meaningful Constraints: Crafting Resonant RPGs Through Environmental Storytelling" for more ideas.

Taming the Variable Beast: Addressing the Concerns

While variable timesteps offer advantages, they also present challenges. However, these challenges can be addressed with the right techniques.

Interpolation: Smoothing Out the Bumps

To mitigate potential visual inconsistencies caused by variable update rates and improve frame rate optimization, interpolation can be used to smooth object movement between frames, creating a fluid appearance. This SmoothDamp function softens the visual impact of frame-to-frame changes, reducing perceived “jank” when frame times fluctuate. Here’s an example of linear interpolation in Unity, integrated within a variable timestep context:

// Example of linear interpolation in Unity with variable timestep
public float moveSpeed = 5f; // Units per second
public float smoothSpeed = 0.125f;
private Vector3 _velocity = Vector3.zero;
private Vector3 _targetPosition;

void Update()
{
    //Set target position (example: user input)
    Vector3 targetVelocity = new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));
    _targetPosition = transform.position + targetVelocity;
    transform.position = Vector3.SmoothDamp(transform.position, _targetPosition, ref _velocity, smoothSpeed);
}

The crucial Time.deltaTime ensures consistent movement speed regardless of frame rate fluctuations.

Sub-Stepping: Precision Physics

Sub-stepping prevents objects from passing through each other by calculating physics multiple times per frame. For physics simulations that require high accuracy, sub-stepping can be employed to divide each frame into smaller time steps. Without sub-stepping in a game with complex collisions, fast-moving objects might clip through walls because the collision detection only happens once per frame. Sub-stepping divides that frame into smaller chunks, allowing for more frequent collision checks and preventing these visual errors. This is particularly important in scenarios like the one depicted A high-speed photograph of colliding objects demonstrates the need for precise physics in games, where high-speed collisions demand accurate physics calculations to prevent objects from clipping through each other. This is especially critical in collision-heavy games or those with ragdoll physics, where increased accuracy avoids clipping or other visual artifacts.

Determinism Where It Matters

Achieving determinism with variable timesteps requires careful consideration. One technique is frame delay, where inputs are processed with a slight delay to ensure all clients or systems are synchronized before the game state is updated. Frame delay involves buffering inputs for a short period to synchronize game states across different clients, mitigating the effects of network latency or variable processing speeds. For example, a fighting game might buffer player inputs for 2-3 frames. This ensures all players see the same sequence of attacks, even if their connection speeds differ slightly. However, achieving perfect determinism with variable timesteps in complex simulations is extremely challenging and often requires careful architectural considerations and compromises. Implementing variable timesteps in networked games can be challenging, especially when determinism is critical for fair gameplay. While interpolation and other techniques can help, achieving consistent behavior across different clients can be complex and might require alternative approaches or concessions.

The Importance of Measurement: Profiling and Benchmarking

Regardless of the chosen game loop architecture or timestep implementation, profiling and benchmarking are essential. Tools like the Unity Profiler, or custom performance metrics, can identify bottlenecks and optimize performance. Pay close attention to CPU utilization, GPU render times, and memory allocation. Use this data to validate your timestep implementation and identify areas for improvement. For additional performance insights, see "Proactive Unity Editor Performance: Planning, Architecture, and Ownership".

Wayline: Empowering Developers with the Right Tools

Imagine using AI-generated content from a platform like Nextframe. By incorporating variable timesteps, these games can scale more effectively across a wider range of hardware, ensuring a smoother player experience regardless of their system’s capabilities.

At Wayline, we understand the challenges developers face when optimizing their games. Strafekit offers a vast library of high-quality assets, including complex particle systems and detailed animation sequences whose smoothness can be significantly enhanced by variable timestep implementations.

Conclusion: A New Perspective on Time

The decision to use a fixed or variable timestep depends on the specific requirements of the game. While fixed timesteps offer the illusion of simplicity, they can introduce unnecessary constraints and limit the potential of modern hardware. So, implement sub-stepping in your next physics-based prototype, measure the performance difference (CPU usage, frame rate stability) compared to a fixed timestep, and share your findings in the Wayline Discord or your favorite game dev forum. The future of smoother, more scalable games depends on it.