Frosted Glass

Two Methods for Simulating Frosted Glass Surfaces

Light scattering through rough transparent surfaces presents distinct rendering hurdles in real-time graphics. Frosted Glass approaches this by offering two separate technical implementations: a traditional Surface Material and a camera-driven Post Process Material. Each architecture balances performance, coloration control, and translucency handling differently, allowing them to serve distinct roles or merge within the same environment.

The Surface Material version evaluates directly on geometry. It gives artists per-surface control over diffuse color, which makes it well-suited for colored panels, decorative partitions, and stained glass window designs. It also retains independent per-surface reflection color. The trade-off with this approach lies in sorting: the Surface Material cannot render other translucent objects positioned behind the frosted pane. On mobile platforms, this material runs in a lower-quality profile to preserve rendering budgets.

The Post Process Material shifts light scattering to screen space through scene-depth masking. Instead of per-surface diffuse values, diffuse coloration is driven per post process volume, while reflection color still functions on a per-surface basis. Its primary technical advantage is scene coherence: it renders translucent objects located behind the frosted glass without sorting dropouts. For mobile deployment, the post process implementation maintains full visual quality.

Surface Material Workflow and Backface Culling Controls

Deploying the surface variation requires applying one of the included frosted glass materials directly to target static or skeletal meshes. Once assigned, light dispersion and surface highlights appear immediately without extra volume configuration.

Complex models with interior faces or overlapping geometric shells can introduce self-overlapping shading artifacts. To counter this, the material instance includes a backface culling toggle. When activating backface culling inside the material instance parameters, the associated mesh must have Render CustomDepth Pass enabled in its actor details. This setting resolves self-intersection boundaries and clears up visual glitches along tight corners or layered panes.

Because the surface method natively handles individual diffuse tinting per material slot, it provides the most direct route for architectural stained glass. Varied colored panes across an ornate frame can be shaded using independent material instances, each carrying custom diffuse and reflection tints without requiring dedicated scene volumes.

Configuring the Post Process Material and Stencil Passes

The post process method relies on custom depth buffers to isolate which screen pixels should receive frosted diffusion. Setting up this pipeline requires specific project-level and actor-level configurations:

• Open Project Settings and navigate to the rendering options, setting Custom Depth-Stencil Pass to Enabled with Stencil.
• Assign a regular transparent glass material to the target mesh to establish the initial refraction and specular response.
• Select the mesh in the viewport or blueprint, enable Render CustomDepth Pass, and enter a CustomDepth Stencil Value between 1 and 255.
• Place or select a Post Process Volume encompassing the camera view, locate the Post Process Materials array, and add an instance of the frosted glass post process material.

Once bound to the volume, the post process shader reads the stencil index written by the mesh, confining blur and transmitted light scattering strictly to geometry carrying that stencil value. Translucent elements situated behind the glass—such as water planes, particle emitters, or additional glass sheets—remain fully visible through the blur.

Combining Material Types for Multi-Layered Frosted Effects

Rather than treating the surface and post process variants as mutually exclusive, scenes can combine both pipelines to solve difficult transparency layering. The included showcase level maps out these pairings, featuring visual test cases and placed notation cards detailing specific setup logic for each scenario.

A notable use case for combining both systems is multi-layered frosted glass. Stacking multiple surface-only shaders causes the rear layers to disappear due to translucency limitations. By pairing a surface material on the primary glass boundary with a stencil-based post process pass on secondary or interior sheets, scenes can simulate double-pane windows, display cases, or frosted office dividers that blur one another correctly. The workflow also maintains compatibility with Soft Outlines pipelines when blending stylized edge detection with textured glass diffusion.

Addressing Unreal Engine 5 Lumen Reflections and Translucency

Working in Unreal Engine 5.0 introduces specific engine-level behaviors when handling translucent reflection passes. Lumen does not natively generate mirror-like sharp reflections on translucent glass surfaces in this version, often yielding overly soft or blurry specular highlights across frosted planes.

To produce sharp, well-defined specular reflections on glass, disable Lumen translucency reflections globally through the console using the command R.Lumen.TranslucencyReflections.Enable 0. Once disabled, the engine falls back to environment cubemaps, yielding crisp highlights on top of the frosted transmission. If a project relies on static lighting and baked lightmaps, adjust the Global Illumination solution to Screen Space within Project Settings. This mirrors the lighting and reflection capture behavior of Unreal Engine 4, allowing captured reflection probes and precomputed lightmaps to display predictably across translucent objects.

For projects running hardware raytracing, raytraced translucency supports simple frosted glass behavior where both reflected light and transmitted light are scattered simultaneously across the surface.

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