OpenGL Shading Language - Built-In Functions (内置函数)
OpenGL Shading Language - Built-In Functions {内置函数}
- 1. Introduction
- 2. Common Functions
- References
OpenGL Shading Language Documentation
https://docs.vulkan.org/glsl/latest/index.html
Built-In Functions
https://docs.vulkan.org/glsl/latest/chapters/builtinfunctions.html
1. Introduction
The OpenGL Shading Language defines an assortment of built-in convenience functions for scalar and vector operations. Many of these built-in functions can be used in more than one type of shader, but some are intended to provide a direct mapping to hardware and so are available only for a specific type of shader.
OpenGL Shading Language 定义了一系列用于标量和矢量运算的内置函数。其中许多内置函数可用于多种类型的着色器，但有些旨在提供与硬件的直接映射，因此仅适用于特定类型的着色器。
Many of the functions are similar to the same named ones in common C libraries, but they support vector input as well as the more traditional scalar input.
许多函数与常见 C 库中的同名函数类似，但它们支持向量输入以及更传统的标量输入。
Applications should be encouraged to use the built-in functions rather than do the equivalent computations in their own shader code since the built-in functions are assumed to be optimal (e.g. perhaps supported directly in hardware).
应该鼓励应用程序使用内置函数，而不是在自己的着色器代码中执行等效计算，因为内置函数被认为是最佳的 (例如，可能直接在硬件中支持)。
User code can replace built-in functions with their own if they choose, by simply redeclaring and defining the same name and argument list. Because built-in functions are in a more outer scope than user built-in functions, doing this will hide all built-in functions with the same name as the redeclared function.
如果用户愿意，只需重新声明和定义相同的名称和参数列表，即可用自己的函数替换内置函数。由于内置函数的作用域比用户内置函数更外层，因此这样做会隐藏所有与重新声明的函数同名的内置函数。
When the built-in functions are specified below, where the input arguments (and corresponding output) can be float, vec2, vec3, or vec4, genFType is used as the argument.
Where the input arguments (and corresponding output) can be int, ivec2, ivec3, or ivec4, genIType is used as the argument.
Where the input arguments (and corresponding output) can be uint, uvec2, uvec3, or uvec4, genUType is used as the argument.
Where the input arguments (or corresponding output) can be bool, bvec2, bvec3, or bvec4, genBType is used as the argument.
Where the input arguments (and corresponding output) can be double, dvec2, dvec3, dvec4, genDType is used as the argument.
For any specific use of a function, the actual types substituted for genFType, genIType, genUType, or genBType have to have the same number of components for all arguments and for the return type.
对于函数的任何特定用途，替换为 genFType、genIType、genUType 或 genBType 的实际类型必须对所有参数和返回类型具有相同数量的组件。
Similarly, mat is used for any matrix basic type with single-precision components and dmat is used for any matrix basic type with double-precision components.
Built-in functions have an effective precision qualification. This qualification cannot be set explicitly and may be different from the precision qualification of the result.
Note: In general, as has been noted, precision qualification is ignored unless targeting Vulkan.
注意：一般来说，如前所述，除非针对 Vulkan，否则精度限定将被忽略。
2. Common Functions
genFType fma(genFType a, genFType b, genFType c)
genDType fma(genDType a, genDType b, genDType c)
Computes and returns a * b + c.
In uses where the return value is eventually consumed by a variable declared as precise:
-
fma()is considered a single operation, whereas the expressiona * b + cconsumed by a variable declared precise is considered two operations. -
The precision of
fma()can differ from the precision of the expressiona * b + c. -
fma()will be computed with the same precision as any otherfma()consumed by a precise variable, giving invariant results for the same input values ofa,b, andc.
Otherwise, in the absence of precise consumption, there are no special constraints on the number of operations or difference in precision between fma() and the expression a * b + c.
References
[1] Yongqiang Cheng, https://yongqiang.blog.csdn.net/