Vertex (computer graphics)

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For other uses, see Vertex (disambiguation).

A vertex (plural vertices) in computer graphics is an object, that has certain attributes, one of which is its position. A vertex is a data structure, that describes certain attributes, among which, the position of a point in 2D or 3D space. Display objects are composed of arrays of flat surfaces (typically triangles) and vertices define the location and other attributes of the corners of the surfaces.

The attributes can represent pretty much anything, e.g. temperature, velocity or direction.

Application to object models[edit]

In computer graphics, objects are most-often represented as triangulated polyhedra. Non triangular surfaces can be converted to an array of triangles through tessellation. The vertices of triangles are associated not only with position but also with other graphical attributes used to render the object correctly. Such attributes can include color at the vertex point, reflectance of the surface at the vertex, textures of the surface at the vertex, and the normal of an approximated curved surface at the location of the vertex. These properties are used in rendering by a vertex shader or vertex pipeline.

The normal can be used to determine a surface's orientation toward a light source for flat shading using Lambert's cosine law, or the orientation of each of the vertices to mimic a curved surface with Phong shading.

Vertex attributes[edit]

Most attributes of a vertex represent vectors in the space to be rendered. Vectors can be 1 (x), 2 (x, y), or 3 (x, y, z) dimensional and can include a fourth homogeneous coordinate (w).

The following is a table of built in attributes of vertices in the OpenGL standard.

OpenGL vertex attributes[1]
GL attribute name attribute defined (data value size)
gl_Vertex Position (vec4)
gl_Normal Normal (vec4)
gl_Color Primary color of vertex (vec4)
gl_MultiTexCoord0 Texture coordinate of texture unit 0 (vec4)
gl_MultiTexCoord1 Texture coordinate of texture unit 1 (vec4)
gl_MultiTexCoord2 Texture coordinate of texture unit 2 (vec4)
gl_MultiTexCoord3 Texture coordinate of texture unit 3 (vec4)
gl_MultiTexCoord4 Texture coordinate of texture unit 4 (vec4)
gl_MultiTexCoord5 Texture coordinate of texture unit 5 (vec4)
gl_MultiTexCoord6 Texture coordinate of texture unit 6 (vec4)
gl_MultiTexCoord7 Texture coordinate of texture unit 7 (vec4)
gl_FogCoord Fog Coord (float)

See also[edit]

For how vertices are processed on 3D graphics cards, see shader.

References[edit]

  1. ^ Christen, Martin. "Clockworkcoders Tutorials: Vertex Attributes". Khronos Group. Retrieved 26 January 2009.