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Ashading language is a graphicsprogramming language made for programmingshader effects on thegraphics processing unit (unlike other programming languages, which send instructions to thecentral processing unit instead). Because of this, shading languages are usually more 'low level' languages and usually consist of specialdata types like "vector", "matrix", "color" and "normal".[citation needed]
Shading languages used inoffline rendering tend to be close tonatural language, so that no special knowledge of programming is required. Offline rendering aims to produce maximum-quality images, at the cost of greater time and compute than real-time rendering.[citation needed]
TheRenderMan Shading Language[1] (RSL or SL, for short), defined in theRenderMan Interface Specification, is a common shading language for production-quality rendering. It is also one of the first shading languages ever implemented.[citation needed]
It defines six major shader types:[citation needed]
Houdini VEX (Vector Expressions) shading language (often abbreviated to "VEX") is closely modeled after RenderMan. However, its integration into a complete 3D package means that the shader writer can access the information inside the shader, a feature that is not usually available in a rendering context. The language differences between RSL and VEX are mainly syntactic, in addition to differences regarding the names of severalshadeop names.[2]
Gelato's[3] shading language, likeHoudini's VEX, is closely modeled after RenderMan. The differences between Gelato Shading Language and RSL are mainly syntactical — Gelato uses semicolons instead of commas to separate arguments in function definitions and a fewshadeops have different names and parameters.[citation needed]
Open Shading Language (OSL) was developed bySony Pictures Imageworks for use in itsAutodesk Arnold Renderer. It is also used byBlender's Cycles render engine. OSL's surface and volume shaders define how surfaces or volumes scatter light in a way that allows for importance sampling; thus, it is well suited forphysically-based renderers that supportray tracing andglobal illumination.[citation needed]
Shading languages forreal-time rendering are now widespread. They provide both higher hardware abstraction and a more flexible programming model than previous paradigms, which hardcoded transformation and shading equations. They deliver more control and richer content with less overhead.[citation needed]
Shaders that are designed to be executed directly on theGPU became useful for high-throughput general processing because of theirstream programming model; this led to the development ofcompute shaders running on similar hardware (see also:GPGPU).[citation needed]
Historically, a few such languages dominated the market;[citation needed] they are described below.
TheOpenGL Architecture Review Board established theARB assembly language in 2002 as a standard low-level instruction set for programmable graphics processors.[4]
High-levelOpenGL shading languages often compile to ARB assembly for loading and execution. Unlike high-level shading languages, ARB assembly does not support control flow or branching. However, it continues to be used when cross-GPU portability is required.[citation needed]
Also known asGLSL orglslang, this standardized shading language is meant to be used withOpenGL.[5]
The language unifiesvertex andfragment processing in a single instruction set, allowing conditional loops andbranches. GLSL was preceded by theARB assembly language.[6]
TheCg language, developed byNvidia,[7] was designed for easy and efficient production pipeline integration. It features API independence and comes with many free tools[1] to improve asset management. Development of Cg was stopped in 2012, and the language is now deprecated.[citation needed]
The shader assembly language in Direct3D 8 and 9 is the main programming language forvertex andpixel shaders inShader Model 1.0/1.1, 2.0, and 3.0. It is a direct representation of the intermediate shader bytecode which is passed to the graphics driver for execution.[citation needed]
The shader assembly language cannot be directly used to program unified Shader Model 4.0, 4.1, 5.0, and 5.1, although it retains its function as a representation of the intermediate bytecode for debug purposes.[8]
TheHigh-Level Shading Language (HLSL) is a C-style shader language forDirectX 9 and higher and Xbox game consoles. It is related to Nvidia's Cg, but is only supported by DirectX and Xbox. HLSL programs are compiled into bytecode equivalent of DirectX shader assembly language.[citation needed]
HLSL was introduced as an optional alternative to the shader assembly language in Direct3D 9, but became a requirement in Direct3d 10 and higher, where the shader assembly language is deprecated.[citation needed]
Adobe Systems addedPixel Bender as part of theAdobe Flash 10 API. Pixel Bender could only process pixel but not 3D-vertex data. Flash 11 introduced an entirely new 3D API calledStage3D, which uses its own shading language calledAdobe Graphics Assembly Language (AGAL), which offers full 3D acceleration support.[9][10] GPU acceleration for Pixel Bender was removed in Flash 11.8.[11][12]
AGAL is a low-level but platform-independent shading language, which can be compiled, for example,to theARB assembly language[citation needed] orGLSL.
Sony announcedPlayStation Shader Language (PSSL) as a shading language similar to Cg/HLSL, but specific to thePlayStation 4. PSSL is said to be largely compatible with the HLSL shader language from DirectX 12, but with additional features for the PS4 and PS5 platforms.[13]
Apple has created a low-levelgraphics API, calledMetal, which runs on mostMacs made since 2012,iPhones since the5S, andiPads since theiPad Air. Metal has its own shading language called Metal Shading Language (MSL), which is based onC++14 and implemented usingclang andLLVM. MSL unifies vertex, fragment and compute processing.[14]
WebGPU Shading Language (WGSL) is the shader language forWebGPU. That is, an application using the WebGPU API uses WGSL to express the programs, known as shaders, that run on the GPU.[15]
To port shaders from one shading language to another, a few approaches are used:[16]
