GLSLANG Spec 4.0 - OpenGL

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4 Variables and Types The order of execution of a tessellation control shader invocation relative to the other invocations for the same input patch is undefined unless the built-in function barrier() is used. This provides some control over relative execution order. When a shader invocation calls barrier(), its execution pauses until all other invocations have reached the same point of execution. Output variable assignments performed by any invocation executed prior to calling barrier() will be visible to any other invocation after the call to barrier() returns. Because tessellation control shader invocations execute in undefined order between barriers, the values of per-vertex or per-patch output variables will sometimes be undefined. Consider the beginning and end of shader execution and each call to barrier() as synchronization points. The value of an output variable will be undefined in any of the three following cases: 1. At the beginning of execution. 2. At each synchronization point, unless • the value was well-defined after the previous synchronization point and was not written by any invocation since, or • the value was written by exactly one shader invocation since the previous synchronization point, or • the value was written by multiple shader invocations since the previous synchronization point, and the last write performed by all such invocations wrote the same value. 3. When read by a shader invocation, if • the value was undefined at the previous synchronization point and has not been writen by the same shader invocation since, or • the output variable is written to by any other shader invocation between the previous and next synchronization points, even if that assignment occurs in code following the read. Fragment outputs output per-fragment data and are declared using the out storage qualifier. It is an error to use centroid out, sample out, or patch out in a fragment shader. Fragment outputs can only be float, floating-point vectors, signed or unsigned integers or integer vectors, or arrays of any these. Matrices and structures cannot be output. Fragment outputs are declared as in the following examples: out vec4 FragmentColor; out uint Luminosity; 4.3.7 Interface Blocks Input, output, and uniform variable declarations can be grouped into named interface blocks to provide coarser granularity backing than is achievable with individual declarations. They can have an optional instance name, used in the shader to reference their members. An output block of one programmable stage is backed by a corresponding input block in the subsequent programmable stage. A uniform block is backed by the application with a buffer object. It is illegal to have an input block in a vertex shader or an output block in a fragment shader; these uses are reserved for future use. An interface block is started by an in, out, or uniform keyword, followed by a block name, followed by an open curly brace ( { ) as follows: interface-block : layout-qualifier opt interface-qualifier block-name { member-list } instance-name opt ; 38
4 Variables and Types layout-qualifier : layout ( layout-qualifier-id-list ) interface-qualifier : in out uniform layout-qualifier-id-list comma separated list of layout-qualifier-id member-list : member-declaration member-declaration member-list member-declaration : layout-qualifier opt qualifiers opt type declarators ; instance-name : identifier identifier [ ] identifier [ integral-constant-expression ] Each of the above elements is discussed below, with the exception of layout qualifiers (layout-qualifier), which are defined in the next section. First, an example, uniform Transform { mat4 ModelViewMatrix; mat4 ModelViewProjectionMatrix; uniform mat3 NormalMatrix; float Deformation; }; // allowed restatement of qualifier The above establishes a uniform block named “Transform” with four uniforms grouped inside it. Types and declarators are the same as for other input, output, and uniform variable declarations outside blocks, with these exceptions: • initializers are not allowed • sampler types are not allowed • structure definitions cannot be nested inside a block Otherwise, built-in types, previously declared structures, and arrays of these are allowed as the type of a declarator in the same manner they are allowed outside a block. 39
Page 1 and 2: The OpenGL ® Shading Language Lang
Page 3 and 4: Table of Contents 1 Introduction...
Page 5: 6.1.2 Subroutines..................
Page 8 and 9: 1 Introduction 1.1 Acknowledgments
Page 10 and 11: 1 Introduction 1.3 Overview This do
Page 12 and 13: 2 Overview of OpenGL Shading Tessel
Page 14 and 15: 3 Basics 3.3 Preprocessor There is
Page 16 and 17: 3 Basics Preprocessor expressions w
Page 18 and 19: 3 Basics By default, compilers of t
Page 20 and 21: 3 Basics centroid flat smooth noper
Page 22 and 23: 3 Basics nondigit: one of _ a b c d
Page 24 and 25: 4 Variables and Types All variables
Page 26 and 27: 4 Variables and Types Floating Poin
Page 28 and 29: 4 Variables and Types 4.1.3 Integer
Page 30 and 31: 4 Variables and Types 4.1.4 Floats
Page 32 and 33: 4 Variables and Types 4.1.8 Structu
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Page 36 and 37: 4 Variables and Types There are no
Page 38 and 39: 4 Variables and Types 4.3 Storage Q
Page 40 and 41: 4 Variables and Types 4.3.4 Inputs
Page 42 and 43: 4 Variables and Types Fragment inpu
Page 46 and 47: 4 Variables and Types If no optiona
Page 48 and 49: 4 Variables and Types When using Op
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Page 52 and 53: 4 Variables and Types By default, g
Page 54 and 55: 4 Variables and Types layout-qualif
Page 56 and 57: 4 Variables and Types None of these
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Page 60 and 61: 4 Variables and Types For example:
Page 62 and 63: 4 Variables and Types • The textu
Page 64 and 65: 4 Variables and Types Some examples
Page 66 and 67: 5 Operators and Expressions 5.2 Arr
Page 68 and 69: 5 Operators and Expressions Some us
Page 70 and 71: 5 Operators and Expressions The arg
Page 72 and 73: 5 Operators and Expressions 5.6 Mat
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Page 76 and 77: 5 Operators and Expressions • The
Page 78 and 79: 5 Operators and Expressions And mat
Page 80 and 81: 6 Statements and Structure iteratio
Page 82 and 83: 6 Statements and Structure f(vec4,
Page 84 and 85: 6 Statements and Structure 6.1.2 Su
Page 86 and 87: 6 Statements and Structure 6.3 Iter
Page 88 and 89: 7 Built-in Variables 7.1 Built-In L
Page 90 and 91: 7 Built-in Variables In the fragmen
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7 Built-in Variables The values in
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7 Built-in Variables in float gl_Fo
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7 Built-in Variables // // Depth ra
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7 Built-in Variables // // compatib
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8 Built-in Functions The OpenGL Sha
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8 Built-in Functions Syntax genType
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8 Built-in Functions 8.3 Common Fun
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8 Built-in Functions 8.4 Floating-P
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8 Built-in Functions 8.5 Geometric
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8 Built-in Functions 8.6 Matrix Fun
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8 Built-in Functions 8.7 Vector Rel
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8 Built-in Functions 8.8 Integer Fu
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8 Built-in Functions 8.9 Texture Fu
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8 Built-in Functions float ComputeA
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8 Built-in Functions Syntax gvec4 t
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8 Built-in Functions Syntax (deprec
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8 Built-in Functions 6. Derivatives
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8 Built-in Functions • The spatia
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8 Built-in Functions Multiple outpu
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9 Shading Language Grammar TBD: sub
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9 Shading Language Grammar function
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9 Shading Language Grammar inclusiv
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9 Shading Language Grammar paramete
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9 Shading Language Grammar IN OUT C
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9 Shading Language Grammar SAMPLER2
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9 Shading Language Grammar compound
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GLSLANG Spec 4.0 - OpenGL

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