texcoord

Texcoord, short for texture coordinate, refers to the coordinates used to sample a texture when rendering a surface. Most commonly, a texcoord consists of two components, (u, v), defined in the texture’s coordinate space and typically in the range [0, 1]. These coordinates map points on a surface to points in a texture image, enabling the texture to appear on the geometry.

Texcoords are usually supplied per vertex as part of the vertex data. During rasterization, values are interpolated across the primitive to produce a per-fragment texcoord. This interpolation is generally perspective-correct to preserve texture alignment on surface curvatures. The resulting texcoord is then used by the shading pipeline to fetch texel data from a texture via a sampling operation.

Textures can be more than simple 2D images. 3D textures use three coordinates (u, v, w) for volumetric sampling, while cube maps use a directional vector to sample one of six square faces. In practice, texcoords are often stored as vertex attributes, passed through the shader, and used with texture sampling functions in the shading language.

Wrapping and filtering control how texcoords outside the standard range are handled and how texture data is interpolated. Wrap modes include repeat, mirrored repeat, clamp to edge, and clamp to border. Filtering options range from nearest and linear to mipmapping and anisotropic filtering, affecting how texels contribute to sampled color, especially at small or distant texcoords or with minified textures.

In shader code, texcoords are fed into texture samplers to obtain color data for rendering. Different graphics APIs and shading systems provide various naming conventions and semantics for handling texcoords, but the underlying concept remains consistent: mapping surface coordinates to texture samples to determine final pixel color.