Unreal Engine 5 Virtual Shadow Maps Guide: Shadow Settings for Architectural Scenes

Virtual Shadow Maps (VSM) is a method for rendering high-resolution shadows in Unreal Engine 5, designed to work with Nanite. Epic Games’ official documentation explains how to configure VSM, particularly in scenes with detailed geometry and dynamic lighting. This guide looks at the project settings, light parameters, and quality-performance trade-offs covered in the Unreal Engine 5 documentation, with architectural visualization workflows in mind.

Which scenes are Virtual Shadow Maps suited to?

VSM aims to produce high-resolution shadows by processing virtual shadow maps according to the needs of on-screen pixels. The maps have a virtual resolution of 16K × 16K and are divided into 128 × 128-pixel pages. Required pages are allocated and rendered, while available pages are cached between frames. Pages may need to be rendered again if they are invalidated by moving objects or lights.

This method is designed for projects that are compatible with Nanite. Using traditional shadow maps with Nanite geometry and Stationary lights is not supported; projects that use Nanite should use Movable Lights or VSM instead. VSM may not be suitable for projects that do not use Nanite or for the target platform. When choosing a shadowing method, consider both the scene geometry and whether the lights are stationary or movable.

1. Check the shadowing method in your project

Open the Shadows section under Engine > Rendering in Project Settings. Choose either Virtual Shadow Maps or traditional Shadow Maps from the Shadow Map Method option. VSM is enabled by default in new projects. In projects created before Unreal Engine 5.0, however, you need to enable it in Project Settings or with the r.Shadow.Virtual.Enable console variable.

When enabled, VSM replaces some other shadowing methods, including precomputed shadows for Stationary lights, pre-shadows, per-object shadows, and Cascaded Shadow Maps. However, fully baked shadows from Static lights continue to work through lightmaps in scenarios that do not use Lumen. With Stationary lights, indirect lighting can come from baked lightmaps, while direct lighting and shadows are calculated dynamically.

2. Set the light source size to suit the scene

Shadow Map Ray Tracing (SMRT) takes samples alongside VSM to create softness and contact hardening in shadows. For local lights, Source Radius affects how rays are distributed relative to the light source; for Directional Lights, this is controlled by Source Angle. Depending on the type of light, an appropriate source size can produce softer shadows.

Treat the values in the table as starting points; no single setting will produce the same result in every scene. Epic’s documentation notes that very large Source Radius or Source Angle values can increase performance costs and cause visual artifacts in the penumbra when the camera is close to the shadow. After increasing the light source size, check the result from different camera positions.

3. Balance sampling quality and performance

Set the ray count for local lights with r.Shadow.Virtual.SMRT.RayCountLocal and for directional lights with r.Shadow.Virtual.SMRT.RayCountDirectional. To set the number of samples per ray, use r.Shadow.Virtual.SMRT.SamplesPerRayLocal and r.Shadow.Virtual.SMRT.SamplesPerRayDirectional. Fewer shadow samples can reduce processing costs, but they also limit the achievable penumbra softness. Epic notes that 4–8 samples per ray produce good results.

Setting the variable that controls the ray count to zero disables SMRT and switches to sharp, single-sample shadows. When Shadows scalability is set to Epic, the default ray count is eight for local and directional lights. As you adjust the settings, keep an eye on shadow noise, softness, and scene performance together.

The VSM cache is enabled by default. If camera movement reveals areas that were not previously visible, new shadow pages may need to be rendered. For that reason, measuring performance from a fixed camera alone may not be enough; test scenes with camera movement as well. The r.Shadow.Virtual.Cache 0 variable disables the cache for debugging. For normal use, the documentation recommends leaving the cache enabled by default.

4. What to consider in an architectural visualization workflow

For architectural scenes with Nanite geometry and dynamic lights, VSM aims to provide high-resolution shadows with a simpler setup. In interiors, set the source size of local lights according to the scene’s lighting character; in exteriors, consider the Directional Light’s Source Angle. Increasing the light source size does not always produce a better result; assess softness, noise, and performance together.

First, confirm the project’s Unreal Engine version, whether it uses Nanite, and which shadowing method is selected. Then adjust the light settings in small steps and check the results in both still images and camera movement. The documentation does not specify a hardware requirement or a single performance figure that applies to every project. That makes testing the settings in the target scene especially important for work with dense geometry and dynamic lights.

Common mistakes

• Assuming VSM is enabled automatically in projects created before Unreal Engine 5.0. Check the project setting and, if needed, the console variable.

• Using Nanite with the traditional shadow map method for Stationary lights. The documentation says this combination is not supported; consider Movable Lights or VSM.

• Increasing Source Radius or Source Angle more than necessary. This can affect performance and cause penumbra artifacts.

• Overlooking that reducing the sample count also limits shadow softness.

• Testing only with a fixed camera. Camera movement may cause previously unseen shadow pages to be rendered.