Edge wear

Edge wear is the damage that collects on the exposed edges of an object: paint chipped off a metal corner, bare wood showing on the rim of a table, a steel step polished bright where boots land. Edges stick out, so they get knocked, rubbed and scraped first. Adding wear there is one of the quickest ways to make a surface look used and to show off its form, because a thin bright line catches the eye along every bevel.

It is also easy to overdo: a prop outlined in uniform silver scratches is a common beginner mistake.

#How edge wear is generated

Most edge wear starts as a mask: white where wear shows, black where it does not. The mask then blends a worn material (bare metal, raw wood) over the finished one.

The key input is curvature: a map that is light on convex edges, dark in concave corners and mid-grey on flat areas. Blender's Pointiness output describes the same idea per vertex: "Lighter values indicate convex angles, darker values indicate concave angles", which "allows you to do effects like dirt maps and wear-off effects" (Blender Manual: Geometry Node).

Painter's Metal Edge Wear generator shows the full set of inputs. It needs baked position, curvature, ambient occlusion and world-space normal maps, and exposes, among others (Substance 3D Painter documentation: Metal Edge Wear):

• Wear Level and Wear Contrast: how much wear, and how hard its border is.
• Curvature Weight: how much the edges drive the result. Adobe warns that "a very low Curvature weight can remove all edge wear, leaving only the grunge."
• Ambient Occlusion Masking: keeps occluded areas from receiving wear, since recessed edges are protected.
• Grunge Amount and Grunge Scale: the noise that breaks the mask up.
• Curvature Type: Standard (sharp), Sobel (slightly blurrier) or Smooth (blurred at several levels, which can lose detail).

A clean bake is therefore needed, because curvature artefacts become wear in the wrong places (see fixing baking artefacts).

#Four places to create edge wear

1. In the texture, from a generator. The common route for uniquely textured props, often as part of a smart material.
2. Painted by hand, on top of or instead of a generator, where the story puts it: handles, steps, the corner a door keeps hitting. See sculpting damage and wear for sculpted chips.
3. Baked into a trim sheet, so every asset that uses the trim inherits the wear along its bevels. See trim sheets.
4. In the shader at runtime, from vertex colour, a mask or curvature computed on the fly, which lets the same mesh be clean in one place and worn in another. See vertex painting and blending and material layers and Substrate.

Runtime edge detection is possible too. In a Polycount thread, Obscura shared an Unreal material function that finds edges "in realtime" on meshes with bevelled edges and face-weighted normals, removing the need to bake curvature, but noted it "suffers from strong aliasing at distance" (Polycount: FWVN edge wear material function for dynamic…).

#Related terms

smart materials · sculpting damage and wear · unique texturing · trim sheets · ambient occlusion · baking · vertex painting and blending · geodecals

#Further reading and watching