Editing Shader (section)

== Design ==
Shaders are simple programs that describe the traits of either a [[Vertex (computer graphics)|vertex]] or a [[pixel]]. Vertex shaders describe the attributes (position, [[Texture mapping|texture coordinates]], colors, etc.) of a vertex, while pixel shaders describe the traits (color, [[Z-buffering|z-depth]] and [[Alpha compositing|alpha]] value) of a pixel. A vertex shader is called for each vertex in a [[Geometric primitive|primitive]] (possibly after [[Tessellation (computer graphics)|tessellation]]); thus one vertex in, one (updated) vertex out. Each vertex is then rendered as a series of pixels onto a surface (block of memory) that will eventually be sent to the screen.

Shaders replace a section of the graphics hardware typically called the Fixed Function Pipeline (FFP), so-called because it performs [[Computer graphics lighting|lighting]] and texture mapping in a hard-coded manner. Shaders provide a programmable alternative to this hard-coded approach.<ref>{{cite web|url=http://www.directx.com/shader/|title=ShaderWorks' update - DirectX Blog|date=August 13, 2003}}</ref>

The basic [[graphics pipeline]] is as follows:

* The CPU sends instructions (compiled [[shading language]] programs) and geometry data to the graphics processing unit, located on the graphics card.
* Within the vertex shader, the geometry is transformed.
* If a geometry shader is in the graphics processing unit and active, some changes of the geometries in the scene are performed.
* If a tessellation shader is in the graphics processing unit and active, the geometries in the scene can be [[Subdivision (computer graphics)|subdivided]].
* The calculated geometry is triangulated (subdivided into triangles).
* Triangles are broken down into [[fragment quads]] (one fragment quad is a 2&nbsp;×&nbsp;2 fragment primitive).
* Fragment quads are modified according to the fragment shader.
* The depth test is performed; fragments that pass will get written to the screen and might get blended into the [[frame buffer]].

The graphic pipeline uses these steps in order to transform three-dimensional (or two-dimensional) data into useful two-dimensional data for displaying. In general, this is a large pixel matrix or "[[frame buffer]]".