The ability to write shaders that can be used on any hardware vendor's graphics card that supports the OpenGL Shading Language.Cross-platform compatibility on multiple operating systems, including Linux, macOS and Windows.It was the first major revision to OpenGL since the creation of OpenGL 1.0 in 1992. Originally introduced as an extension to OpenGL 1.4, GLSL was formally included into the OpenGL 2.0 core in 2004 by the OpenGL ARB. The OpenGL ARB created the OpenGL Shading Language to provide a more intuitive method for programming the graphics processing unit while maintaining the open standards advantage that has driven OpenGL throughout its history. Originally, this functionality was achieved by writing shaders in ARB assembly language – a complex and unintuitive task. Programmability at this level is achieved with the use of fragment and vertex shaders.

With advances in graphics cards, new features have been added to allow for increased flexibility in the rendering pipeline at the vertex and fragment level. It was created by the OpenGL ARB (OpenGL Architecture Review Board) to give developers more direct control of the graphics pipeline without having to use ARB assembly language or hardware-specific languages. OpenGL Shading Language ( GLSL) is a high-level shading language with a syntax based on the C programming language. The compiled programs are executed on the GPU. Shaders are written in OpenGL Shading Language and compiled. Video games outsource rendering calculations to the GPU over OpenGL in real-time.

Glsl opengl es 2.0 spec