Micropolygon - AbsoluteAstronomy.com

3D computer graphics

3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...

, a micropolygon (or µ-polygon) is a polygon

Polygon

In geometry a polygon is a flat shape consisting of straight lines that are joined to form a closed chain orcircuit.A polygon is traditionally a plane figure that is bounded by a closed path, composed of a finite sequence of straight line segments...

that is very small relative to the image being rendered.
Commonly, the size of a micropolygon is close to or even less than the area of a pixel

Pixel

In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....

. Micropolygons allow a renderer to create a highly detailed image.

The concept of micropolygons was developed within the Reyes

Reyes rendering

Reyes rendering is a computer software architecture used in 3D computer graphics to render photo-realistic images. It was developed in the mid-1980s by Loren Carpenter and Robert L. Cook at Lucasfilm's Computer Graphics Research Group, which is now Pixar. It was first used in 1982 to render images...

algorithm

Algorithm

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

, in which geometric primitives are tessellated at render time into a rectangular grid of tiny, four-sided polygons. A shader

Shader

In the field of computer graphics, a shader is a computer program that is used primarily to calculate rendering effects on graphics hardware with a high degree of flexibility...

might fill each micropolygon with a single color or assign colors on a per-vertex

Vertex (geometry)

In geometry, a vertex is a special kind of point that describes the corners or intersections of geometric shapes.-Of an angle:...

basis. Shaders that operate on micropolygons can process an entire grid of them at once in SIMD

SIMD

Single instruction, multiple data , is a class of parallel computers in Flynn's taxonomy. It describes computers with multiple processing elements that perform the same operation on multiple data simultaneously...

fashion. This often leads to faster shader execution, and allows shaders to compute spatial derivatives

Derivative

In calculus, a branch of mathematics, the derivative is a measure of how a function changes as its input changes. Loosely speaking, a derivative can be thought of as how much one quantity is changing in response to changes in some other quantity; for example, the derivative of the position of a...

(e.g. for texture filtering

Reconstruction filter

In a mixed-signal system , a reconstruction filter is used to construct a smooth analogue signal from a digital input, as in the case of a digital to analogue converter or other sampled data output device....

) by comparing values at neighboring micropolygon vertices.

Furthermore, a renderer using micropolygons can support displacement mapping

Displacement mapping

Displacement mapping is an alternative computer graphics technique in contrast to bump mapping, normal mapping, and parallax mapping, using a texture- or height map to cause an effect where the actual geometric position of points over the textured surface are displaced, often along the local...

simply by perturbing micropolygon vertices during shading. This displacement is usually not limited to the local surface normal but can be given an arbitrary direction.

Further reading