perVertex

Pervertex, often written as per-vertex or pervertex, is a term used in computer graphics to describe data, operations, or shading that are associated with individual vertices of a polygonal mesh. In a typical 3D mesh, vertices define points in space, and per-vertex data is defined at these points and then interpolated across the surface of each polygon during rendering. Common per-vertex data includes position, normal vectors, vertex colors, texture coordinates, and, for skinning, bone weights and indices.

In rendering pipelines, a vertex shader processes each vertex and outputs attributes that will be interpolated across the primitive to produce per-fragment data. Historically, per-vertex shading followed by interpolation is known as Gouraud shading, where colors are computed at vertices and blended across the triangle. In modern pipelines, per-fragment (per-pixel) shading is often used instead, where lighting calculations rely on attributes that may be interpolated but ultimately evaluated per fragment, typically using interpolated normals.

Per-vertex data is stored in vertex buffers as part of the mesh's geometry. File formats such as OBJ, FBX, and glTF encode per-vertex attributes like position, normal, and texture coordinates and may also include skinning data. During rasterization, attributes are interpolated across the surface, with perspective-correct interpolation ensuring that texture coordinates and other attributes remain visually accurate when transformed to screen space.

Limitations of per-vertex data include the need for higher vertex counts to capture fine geometric and shading detail, since coarse meshes require more interpolation to approximate sharp features. Per-vertex information remains foundational in many real-time applications and in pipelines where vertex-centric processing is central.