Bevel shaders

A bevel shader makes sharp edges look rounded at render time. It changes the shading normals near each edge, the same way a bump map does, but leaves the mesh untouched. Blender describes its Bevel node as a shader "for rendering rounded corners" that, "like bump mapping", affects only shading (Blender Manual: Bevel Node). Redshift calls its version a shading effect that simulates "round beveled edges but without introducing extra geometry" (Redshift documentation: Round Corners).

In game art, bevel shaders are mainly a shortcut for the the high-to-low workflow: you render or bake rounded edges from a simple, sharp-edged model instead of modeling every bevel. bevels and chamfers compares them with the other bevel methods.

#How it works

Redshift's documentation describes the mechanism: the shader sends probe rays to find nearby edges and corners, and the result is fed into the surface's bump input (Redshift documentation: Round Corners). Shading normals within the radius bend towards the neighbouring faces. The settings follow from that:

• Radius or width: how far from the edge the rounding reaches (Blender Manual: Bevel Node; Marmoset Toolbag documentation: Surface module: Bevel settings; Redshift documentation: Round Corners).
• Samples: how many probe rays per shading point. More samples are smoother and slower (Blender Manual: Bevel Node; Redshift documentation: Round Corners).
• Which objects count: whether separate, intersecting objects round against each other (Redshift documentation: Round Corners; Marmoset Toolbag documentation: Surface module: Bevel settings).

The silhouette stays sharp, so large rounded forms still belong in the mesh.

#Three implementations compared

Marmoset's millimetre width needs correct scene scale: a crate imported at the wrong scale gets bevels ten or a hundred times off. See units, scale and axes.

#Bevel shaders in a game-art bake

Marmoset's own tutorial describes the workflow: generating bevels in the material can "eliminate the time-consuming process of adding edge loops for subdivision control", as "an alternative to creating a detailed subdivision surface mesh" (Marmoset: Revolutionize Your 3D Workflow with Toolbag's…). Toolbag cannot bake directly from the low poly, so you still need a high and low pair; for simple assets, a copy of the low poly with a bevel material can serve as the high (Marmoset: Revolutionize Your 3D Workflow with Toolbag's…). It also warns that shadows still come from the raw mesh, so "harsh shadows can appear" where light should wrap round the edge (Marmoset: Revolutionize Your 3D Workflow with Toolbag's…).

#Limits

• Wide bevels. Redshift says the effect "can't represent extremely wide bevels" and advises small radii; at large radii low sample counts give triangular artefacts near corners (Redshift documentation: Round Corners).
• Blocked rays. Some edges may stay unrounded because the probe rays are blocked by the mesh's own sharp geometry; Redshift suggests traditional bevelling in those cases (Redshift documentation: Round Corners).
• Hidden faces. Internal polygons inside intersecting objects create false edges; delete them or boolean the objects (Redshift documentation: Round Corners). See booleans.
• Cost. Blender calls the node "very expensive", best for baking or stills, and notes that the Bevel modifier "is a faster option when it works, but sometimes fails on complex or messy geometry" (Blender Manual: Bevel Node).

#How to set one up

#In Blender (Cycles bake)

This bakes a normal map with rounded edges from a sharp-edged mesh. The example is a 1 m crate with a 2048 px map, so a 4 mm radius covers about 8 px (see the worked example above).

1. Make the source mesh. Duplicate the low poly, or use your blockout if it already has the panels and cuts you want. For simple assets, a copy of the low poly with a bevel material can act as the high poly (Marmoset: Revolutionize Your 3D Workflow with Toolbag's…). Rename the pair, for example crate_high and crate_low.
2. Add the bevel to the source material. In the source mesh's material, add a Bevel node and connect its Normal output to the Normal input of the Principled BSDF (Blender Manual: Bevel Node). Set Radius to 0.004 (4 mm in a metre-scale scene) and raise Samples from the default 4 to 8 or 16 for a cleaner bake (Blender Manual: Bevel Node).
3. Prepare the target. The low poly needs a UV map, and its material needs an Image Texture node with a new 2048 px image; "The active (last selected) Image Texture node is used as the baking target" (Blender Manual: Render Baking). Set the image to Non-Color.
4. Set up the bake. Switch the render engine to Cycles (the Bevel node is Cycles only (Blender Manual: Bevel Node)), choose Bake Type Normal and enable Selected to Active, which bakes "shading on the surface of selected objects to the active object" (Blender Manual: Render Baking). Use a cage or a small Ray Distance so rays reach the source surface (Blender Manual: Render Baking).
5. Bake and check. Select the source mesh, then the low poly last so it is active, and press Bake. Save the image, apply it to the low poly as a normal map, and check the edges under a moving light at 100% and 25% zoom.

#In Marmoset Toolbag

1. Enable ray tracing. The bevel works in Ray Tracing or Hybrid mode and is "not supported in Raster" (Marmoset Toolbag documentation: Surface module: Bevel settings).
2. Add the bevel to the high-poly material. In the material's Surface module, choose the bevel option and set Width in millimetres, so scene scale must be correct (Marmoset Toolbag documentation: Surface module: Bevel settings). Wider bevels need more samples (Marmoset Toolbag documentation: Surface module: Bevel settings).
3. Limit where it rounds. Use Bevel Angle to skip shallow edges, or a vertex colour channel to vary the width per area (Marmoset Toolbag documentation: Surface module: Bevel settings). Different materials on different face groups can carry different widths, as Nathan Young does (Marmoset: Toolbag's Bevel Shader in Action: 3 Artists…).
4. Bake. Toolbag still needs a high and low pair; load both into the baker and bake normal, AO and curvature as usual (Marmoset: Revolutionize Your 3D Workflow with Toolbag's…). See the high-to-low workflow.

#Video tutorials

#Use in recent games

Bevel shaders are a production shortcut inside the bake, so they rarely appear by name in shipped-game breakdowns. The documented cases are artists describing their own production workflow, and studios that solved the same problem with shared baked bevels.

• AAA weapon work. Mohammed "Ace" Omar, a weapons and hard-surface artist who names the Call of Duty franchise as his most notable work, uses Toolbag's bevel shader to bake from mid-poly models instead of building hours-long high polys: "Toolbag's Bevel Shader method takes less than an hour with minimal effort" (Marmoset: Toolbag's Bevel Shader in Action: 3 Artists…). The article does not say which shipped assets were made this way.
• CAD-based high polys. In the same Marmoset article, senior 3D artist Dan Kenton uses the shader to turn CAD models into "a lightweight high poly model that is quicker and easier to iterate on", with softer bevels on plastics (Marmoset: Toolbag's Bevel Shader in Action: 3 Artists…).
• The Last of Us Part I: baked bevels shared through trims. Naughty Dog's Matthew Trevelyan Johns took a different route to the same goal: models with hard edges and 90-degree angles, and bevels taken from shared baked-bevel trims. He estimates about 80% of his Lab assets used them instead of unique bakes (ArtStation: The Last of Us: Part I...Trim Pipeline).

#Related terms

bevels and chamfers · baking · normal map · the high-to-low workflow · the mid-poly workflow · shaders for artists

#Further reading and watching