A reconstructed mesh describes a shape correctly and is built badly. Retopology keeps the shape and replaces the construction.
What is wrong with a raw generated mesh
- Density with no purpose. Hundreds of thousands of triangles distributed by the reconstruction algorithm rather than by where detail actually is. A flat panel gets the same density as a face.
- Irregular topology. Triangles of wildly varying size and shape, with no edge flow following the form.
- No deformation behaviour. Bending a limb needs edge loops running around it. Machine-made topology has none, so a rigged character creases and collapses at the joints.
- Unpredictable subdivision. Smoothing a mesh with irregular topology amplifies the irregularity rather than the form.
What retopology produces
An even quad or triangle mesh at a target density, following the surface. The silhouette is preserved; the wireframe underneath is entirely different.
Choosing a level of detail
- Low. Background props, distant objects, mobile targets, anything where the silhouette is all that survives at viewing distance.
- Medium. The general-purpose choice. Hero props, interactive objects, anything a player gets close to.
- High. Characters that deform, surfaces with fine sculpted detail worth preserving, anything destined for further sculpting.
Choosing too low costs you the silhouette. Choosing too high costs you performance and gives an animator more geometry than a deformation needs.
Quads or triangles
- Quads for anything that will be subdivided, sculpted further, or deformed by a skeleton. Modelling tools and subdivision algorithms both assume quads.
- Triangles for anything going straight into a game engine. Engines triangulate on import anyway, so a quad mesh is a convenience for you rather than for the renderer.
What retopology does not do
It does not add detail. Rebuilding a low-detail mesh at a high polygon count gives you a high-poly mesh of a low-detail shape. Detail comes from the source, or from a normal map baked off a denser version.
It also does not preserve UVs. The mesh is new, so its layout is new — retopology is followed by UV unwrapping, in that order.