GLSL Spec

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8 Built-in Functions 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. The built-in functions basically fall into three categories: • They expose some necessary hardware functionality in a convenient way such as accessing a texture map. There is no way in the language for these functions to be emulated by a shader. • They represent a trivial operation (clamp, mix, etc.) that is very simple for the user to write, but they are very common and may have direct hardware support. It is a very hard problem for the compiler to map expressions to complex assembler instructions. • They represent an operation graphics hardware is likely to accelerate at some point. The trigonometry functions fall into this category. 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. 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). User code can replace built-in functions with their own if they choose, by simply re-declaring 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 re-declared function. When the built-in functions are specified below, where the input arguments (and corresponding output) can be float, vec2, vec3, or vec4, genType 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 genType, genIType, genUType, or genBType have to have the same number of components for all arguments and for the return type. 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. 114
8 Built-in Functions 8.1 Angle and Trigonometry Functions Function parameters specified as angle are assumed to be in units of radians. In no case will any of these functions result in a divide by zero error. If the divisor of a ratio is 0, then results will be undefined. These all operate component-wise. The description is per component. Syntax genType radians (genType degrees) Description Converts degrees to radians, i.e., 180 ⋅degrees genType degrees (genType radians) Converts radians to degrees, i.e., 180 ⋅radians genType sin (genType angle) The standard trigonometric sine function. genType cos (genType angle) The standard trigonometric cosine function. genType tan (genType angle) The standard trigonometric tangent. genType asin (genType x) genType acos (genType x) genType atan (genType y, genType x) genType atan (genType y_over_x) Arc sine. Returns an angle whose sine is x. The range of values returned by this function is [ − 2 , 2 ] Results are undefined if ∣x∣1. Arc cosine. Returns an angle whose cosine is x. The range of values returned by this function is [0, π]. Results are undefined if ∣x∣1. Arc tangent. Returns an angle whose tangent is y/x. The signs of x and y are used to determine what quadrant the angle is in. The range of values returned by this function is [−, ]. Results are undefined if x and y are both 0. Arc tangent. Returns an angle whose tangent is y_over_x. The range of values returned by this function is [ − 2 , 2 ] . 115
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The OpenGL ® Shading Language Lang
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Table of Contents 1 Introduction...
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5.4 Constructors...................
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1 Introduction This document specif
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1 Introduction • Change from ASCI
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1 Introduction 1.4 Error Handling C
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2 Overview of OpenGL Shading writte
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3 Basics string being string 0. Lin
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3 Basics The defined operator can b
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3 Basics By default, compilers of t
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3 Basics 3.5 Tokens The language is
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3 Basics goto inline noinline publi
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4 Variables and Types All variables
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4 Variables and Types Floating Poin
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4 Variables and Types Type usampler
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4 Variables and Types 4.1.4 Floats
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4 Variables and Types 4.1.7.1 Sampl
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4 Variables and Types expression th
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4 Variables and Types 4.1.10 Implic
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4 Variables and Types A list of ini
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4 Variables and Types Within a decl
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4 Variables and Types uniform varia
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4 Variables and Types of any these.
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4 Variables and Types Redeclaration
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4 Variables and Types binding point
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4 Variables and Types Binding point
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GLSL Spec

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