Fixed-function (computer graphics)
Fixed-function is a term canonically used to contrast 3D graphics APIs and earlier GPUs designed prior to the advent of shader-based 3D graphics APIs and GPU architectures.
History
Historically fixed-function APIs consisted of a set of function entry points that would approximately or directly map to dedicated logic for their named purpose in GPUs designed to support them. As shader based GPU]]s and APIs evolved fixed-function APIs were implemented by graphics driver engineers using the more general purpose shading architecture. This approach served as a segue that would continue providing the fixed-function API abstraction most developers were experienced with while allowing further development and enhancements of the newer shader-based architectures.
| 3D API | First Shader-based Version |
|---|---|
| OpenGL | 2.0 |
| OpenGL ES | 2.0 |
| DirectX | 9.0 |
Fixed Function vs Shaders
Fixed function APIs tend to be a simpler programming abstraction with a series of well-defined and specifically named graphics pipeline stages. Shader based APIs treat graphics data (vertices and pixels / texels) generically and allow a great deal of flexibility in how this data is modulated. More sophisticated rendering techniques are possible using a shader based API.