Clustered Rendering in Unreal Engine 5

Unreal Engine 5 (UE5) has introduced a suite of cutting-edge technologies that have fundamentally transformed real-time rendering. Among these, Clustered Rendering is a significant advancement that allows for more efficient handling of complex lighting and shading scenarios in real-time environments. In this blog post, we’ll explore what clustered rendering is, how it works in UE5, and the benefits it brings to developers and gamers.

What is Clustered Rendering?

Clustered rendering is a modern rendering technique designed to efficiently manage lighting, shadows, and other visual effects in 3D scenes. Traditional rendering pipelines often struggle to balance performance and visual fidelity, particularly in complex scenes with many lights and shadow-casting objects. Clustered rendering addresses these challenges by dividing the 3D space into a grid of clusters, each representing a portion of the scene. This spatial partitioning allows the rendering engine to handle lighting and shading calculations more efficiently.

How Does Clustered Rendering Work in UE5?

Clustered rendering in UE5 improves upon earlier techniques such as deferred shading and forward rendering by offering a more flexible and scalable approach to handling lights and shadows. Here’s a breakdown of how clustered rendering operates in Unreal Engine 5:

1. Spatial Partitioning of the Scene

The first step in clustered rendering is dividing the scene into a 3D grid of clusters or cells. Each cluster represents a small volume of the scene and contains information about the objects, lights, and other visual elements within that volume.

Grid-Based Division: The entire 3D space is partitioned into a uniform grid, with each cell in the grid representing a cluster. These clusters are often aligned in view space, meaning they are oriented based on the camera’s perspective to maximize efficiency.
Dynamic Size Adjustment: Clusters can vary in size depending on their distance from the camera and the complexity of the scene. Closer clusters might be smaller to accommodate more detail, while distant clusters can be larger since less detail is needed.

2. Light and Object Association

Once the scene is divided into clusters, each cluster needs to know which lights and objects affect it. This association is crucial for determining which lights contribute to the final shading of objects within each cluster.

Light Culling: The engine performs a process called light culling, which determines which lights are relevant to each cluster. Only lights that affect the cluster (based on their position, range, and intensity) are considered in the shading calculations, significantly reducing the number of lights that need to be processed.
Object Association: Similar to lights, objects are also associated with clusters. Each cluster keeps track of which objects are within its bounds and requires shading. This association allows for more efficient shading calculations and optimizes the rendering process.

3. Efficient Light and Shadow Calculations

Clustered rendering allows for more efficient calculations of lighting and shadows by reducing the number of computations required per frame:

Per-Cluster Shading: Instead of calculating lighting and shadows for every pixel on the screen, clustered rendering performs these calculations on a per-cluster basis. This significantly reduces the computational load, as only the relevant clusters are processed.
Minimized Overdraw: Since clustered rendering works on a 3D grid, it inherently minimizes overdraw — the redundant drawing of pixels covered by other pixels in a scene. This reduction in overdraw helps improve performance, especially in complex scenes with many overlapping objects.

4. Support for Complex Lighting Scenarios

One of the significant advantages of clustered rendering is its ability to handle complex lighting scenarios more efficiently than traditional techniques:

Multiple Light Sources: Clustered rendering excels at managing scenes with multiple dynamic lights, such as point lights, spotlights, and area lights. It allows for the efficient rendering of scenes with dozens or even hundreds of lights without a significant performance hit.
Advanced Shadow Techniques: Clustered rendering also supports advanced shadow techniques, such as soft shadows, volumetric shadows, and dynamic shadow casting from multiple light sources. This capability enhances the realism of the scene while maintaining high performance.

Benefits of Clustered Rendering in Unreal Engine 5

Clustered rendering brings several benefits to the table, making it a valuable tool for game developers working with Unreal Engine 5:

1. Improved Performance in Complex Scenes

Clustered rendering is designed to handle complex scenes with many lights and objects efficiently. By dividing the scene into clusters and performing light and shadow calculations on a per-cluster basis, the rendering process becomes much more efficient.

Reduced Computational Load: By focusing only on the clusters that are visible and relevant, clustered rendering reduces the number of calculations required per frame, leading to improved performance.
Optimized Resource Usage: The technique minimizes the use of GPU resources by culling irrelevant lights and objects, freeing up resources for other tasks.

2. Enhanced Visual Fidelity

Clustered rendering allows for more advanced lighting and shadow techniques, resulting in more realistic and visually appealing scenes:

Rich, Dynamic Lighting: With support for multiple dynamic lights and advanced shadow techniques, developers can create richly lit environments that respond dynamically to player interactions and environmental changes.
High-Quality Shadows: The ability to handle complex shadow scenarios with soft edges and volumetric effects enhances the realism of the scene, contributing to a more immersive experience.

3. Flexibility and Scalability

Clustered rendering is highly flexible and scalable, making it suitable for various game genres and hardware configurations:

Adaptability to Different Hardware: Clustered rendering can be scaled to work efficiently on both high-end and mid-range hardware, ensuring that games remain accessible to a wide range of players.
Compatibility with Other Rendering Techniques: Clustered rendering can be combined with other rendering techniques, such as deferred shading or ray tracing, to achieve specific visual goals or optimize performance further.

4. Support for Modern Rendering Features

Clustered rendering is designed to take full advantage of modern hardware and rendering capabilities, including support for the latest graphics APIs like DirectX 12 and Vulkan:

Advanced Graphics APIs: The technique is optimized for modern graphics APIs, allowing developers to leverage advanced features such as multi-threading and compute shaders for improved performance.
Integration with UE5’s Ecosystem: Clustered rendering works seamlessly with other Unreal Engine 5 features, such as Nanite (virtualized geometry) and Lumen (global illumination), to provide a comprehensive suite of tools for creating next-generation games.

Use Cases for Clustered Rendering

Clustered rendering is versatile and can be applied to various game development scenarios:

Open-World Games: In large, open-world games with complex lighting and shadow scenarios, clustered rendering provides the performance needed to handle dynamic environments efficiently.
First-Person Shooters and Action Games: Games that require dynamic lighting and shadows, such as first-person shooters and action-adventure games, can benefit from the flexibility and efficiency of clustered rendering.
Virtual Reality (VR) and Augmented Reality (AR): In VR and AR applications, where maintaining high frame rates is critical, clustered rendering helps optimize performance while delivering high-quality visuals.