micropolygon

Micropolygon is a unit of geometry used in some computer graphics rendering pipelines, referring to very small polygons used to approximate curved surfaces. In micropolygon rendering, surfaces are subdivided into tiny polygons, on the order of the size of a pixel or smaller, so shading can be computed locally within each polygon. The approach reduces shading artifacts and allows more accurate shading of complex lighting as the surface is approximated by many small facets.

Rendering with micropolygons involves tessellating geometry into micro-polygons, typically triangles or quadrilaterals. Each micropolygon has shading attributes such as color, normals, and texture coordinates. The rasterizer processes each micropolygon to produce fragments within its footprint; depth testing ensures correct visibility. Because each micropolygon is small, lighting can be evaluated per polygon and interpolated across its pixels, producing smooth results on curved surfaces.

Historically, the term and technique were popularized by Pixar in the RenderMan rendering architecture during the 1980s and 1990s. The micropolygon approach enabled photorealistic rendering by separating geometry complexity from shading and by enabling per-polygon shading with fine granularity. In modern real-time graphics and newer renderers, traditional micropolygon rasterization has largely been supplanted by other approaches (e.g., finely tessellated meshes with per-pixel shading), though the concept of subdividing surfaces into small facets remains common.

Characteristics of micropolygon rendering include small polygon sizes, often around a pixel, and the use of tessellation to adapt to viewing conditions. While offering advantages in shading fidelity, it can incur higher memory and processing costs. The concept, however, influenced later shading and tessellation techniques in both offline and real-time graphics.