Even still, occasional artifacts stemming from missing pages can happen, especially around edges of the screen when zoomed in on soft penumbra. A variety of techniques are used to reduce the impact of this, including dilating the page mappings slightly and having various fallbacks in place during iteration. As the algorithm traverses the ray, it can encounter unmapped pages where no shadow data exists. Penumbra Artifactsīy default, Virtual Shadow Maps only guarantees that the samples around the ray origin (the receiver pixel) will be present. Shadows near the base are sharper than those farther away.Įxamples of inconsistent penumbra shadows. Objects that cast shadows farther will have softer shadows than objects casting shadows closer to a shadow-receiving surface.įor example, the mesh pictured below is tall and casts its shadow over a long distance. Shadow Map Ray Tracing (SMRT) is a sampling algorithm used with virtual shadow maps to produce more plausible soft shadows and contact hardening. Ray-traced shadows still take precedence over VSMs as they generally provide the highest quality solution. It still may have value when used to pick up cheaper shadows from objects set to not render into shadow maps but is not recommended otherwise as it will be less accurate than the shadows VSMs will create. Local lights (Point and Spot Lights) are not affected, and selecting Distance Field shadows for these continues to override the active shadow map method.ĭue to VSM's high resolution and accuracy, the screen space Contact Shadow feature controlled with the Contact Shadow Length property is no longer necessary to achieve sharp contact shadows. It is possible to make non-Nanite geometry behave the same way as Nanite by the console variable r. 0. Nanite geometry always renders to the Virtual Shadow Map regardless of distance, since this is the most performant option and provides the highest quality. Using Distance Field Shadows provides a useful tool to reduce runtime costs in complex scenes, such as those with lots of non-Nanite foliage. Distance Field Shadows take over for non-Nanite geometry beyond the dynamic shadowing distance of Movable Lights - set on a Directional Light using the Cascaded Shadow Maps property Dynamic Shadow Distance Movable Light. Stationary lights will use the indirect diffuse contribution from any baked lightmaps, but their direct lighting and shadows are evaluated dynamically (the same as Movable lights) when VSMs are enabled.ĭistance Field Shadows are not replaced, and can be used in tandem with Virtual Shadow Maps for Directional Lights. Their contributions are entirely represented in the baked lightmaps and there is no runtime lighting evaluated at all. Stationary precomputed shadows, including 2D Distance Field and shadow factor 'shadow maps'įully baked shadows from Static Lights will still work as before (when not using Lumen). When VSMs are enabled, they replace a variety of existing shadow methods in Unreal Engine: What happens with existing shadow methods when VSMs are enabled? New projects use Virtual Shadow Maps by default. The pages are cached between frames unless they are invalidated by moving objects or light, which further improves performance.Įxisting projects will need to opt-in using the project setting, or console variable r.

Pages are allocated and rendered only as needed to shade on-screen pixels based on an analysis of the depth buffer.

To keep performance high at reasonable memory cost, VSMs split the shadow map into tiles (or Pages) that are 128x128 each. Clipmaps are used to increase resolution further for Directional Lights.

In their current implementation, they have a virtual resolution of 16k x 16k pixels. Replace the many Stationary Light shadowing techniques with a single, unified pathĬonceptually, virtual shadow maps are just very high-resolution shadow maps. Provide a simple solution that works by default with limited amounts of adjustment needed Plausible soft shadows with reasonable, controllable performance costs Significantly increase shadow resolution to match highly detailed Nanite geometry Virtual Shadow Maps have been developed with the following goals: Virtual Shadow Maps (VSMs) is the new shadow mapping method used to deliver consistent, high-resolution shadowing that works with film-quality assets and large, dynamically lit open worlds using Unreal Engine 5's Nanite Virtualized Geometry, Lumen Global Illumination and Reflections, and World Partition features.

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