UV unwrapping hard-surface objects for games

UV Unwrapping Hard-Surface Objects for Games

Hard-surface UV—task with clear rules and predictable complexities. Cube—simpler than organic, gun barrel—already interesting, spaceship with interior details—several working days just on unwrapping. Principal difference from organic: hard-surface has natural seams along structural element edges, both advantage and trap simultaneously.

Trap is that "obvious" seams along all edges give hundreds of tiny islands packing poorly with low texel density. Good hard-surface unwrap—balance between island count, texel density, seam hiding, and baking correctness.

Hard-surface unwrapping technical complexities

Cylindrical surfaces. Tubes, barrels, handles—cylinder unwraps through one seam along least visible generatrix. Sounds simple until gun handle appears with overlays, decorative grooves and holes. Each hole needs separate handling: either separate island for end faces or seam along hole edges. No automatic solution handles this correctly—manual analysis only.

Planar faces with non-standard angle. Panels, inclined faces, diagonal planes—if applying Project From View without alignment, get trapezoidal islands instead rectangular. For baking and trim sheet texture creation critical: rectangular island packs efficiently, trapezoidal—doesn't.

Overlapping geometry (bolts, rivets, fastening details). For small details repeating many times overlap UV intentionally used for UV space savings. Works only under strict conditions: details identical, baker lighting won't leave visible differences. If even one rivet turned toward light source differently—overlap gives incorrect bake on that detail.

Trim sheets and tiling textures. For architectural elements and technical surfaces trim sheet pipeline often used: narrow texture with detail set (edges, grooves, panels) tiling along surfaces. Trim sheet UV unwrapped differently than standard atlas: important not only texel density but precise island alignment along atlas vertical axis.

Hard-surface object unwrapping process

Model analysis. Determine: what goes to bake (normal map), what becomes tiling texture, what—atlas. For complex assets these categories mix.

Seam placement. Choose edges for seams by priorities: invisible from game camera faces—first priority, interior surfaces—second, structural edges on back sides—third. For weapons: muzzle end, handle bottom edge, interior trigger surface.

Tool. Rizom UV for everything. Maya UV Toolkit—if model already in Maya pipeline and no sense exporting. Blender UV Editor—for simple assets or if model in Blender.

In Rizom UV for hard-surface key tool—Auto Seam with subsequent manual editing plus Straighten UV for aligning straight edges. Rectangular panels should give rectangular islands—requires additional step after Unfold.

Packing. For hard-surface island orientation especially important. Rectangular islands aligned by axes pack significantly better than rotated. UVPackmaster in Blender or built-in Rizom UV packer give good results with proper settings.

Texel density. For weapons and hero props: 512 px/m minimum for 2048 texture. For environment hard-surface (walls, machinery): 256–512 px/m depending on camera distance. Different parts of one asset can have different texel density—normal if justified by zone priority.

Engine-specific considerations

Unreal Engine. Static meshes require second UV channel (channel index 1) for lightmap. Lightmap UV—separate unwrap without overlap, with extra padding (minimum 2px per 64px lightmap resolution, 4px per 128px). Can't be done automatically for hero objects—baked lighting artifacts guaranteed.

Unity. Similar story with Generate Lightmap UVs in import settings. For high-quality static assets—manual lightmap UV in channel 2 (Unity 0-indexed: channel 1).

Timeline guidelines

Cost calculated individually. Lightmap UV channel included in work as separate task specification.