skia / external / github.com / KhronosGroup / OpenGL-Registry / refs/heads/11723-workgroup / . / extensions / EXT / EXT_shader_implicit_conversions.txt

Name | |

EXT_shader_implicit_conversions | |

Name Strings | |

GL_EXT_shader_implicit_conversions | |

Contact | |

Jon Leech (oddhack 'at' sonic.net) | |

Daniel Koch, NVIDIA (dkoch 'at' nvidia.com) | |

Contributors | |

Slawomir Grajewski, Intel | |

Contributors to ARB_gpu_shader5 | |

Notice | |

Copyright (c) 2010-2013 The Khronos Group Inc. Copyright terms at | |

http://www.khronos.org/registry/speccopyright.html | |

Portions Copyright (c) 2013-2014 NVIDIA Corporation. | |

Status | |

Complete. | |

Version | |

Last Modified Date: April 1, 2014 | |

Revision: 6 | |

Number | |

OpenGL ES Extension #179 | |

Dependencies | |

OpenGL ES 3.1 and OpenGL ES Shading Language 3.10 are required. | |

This specification is written against the OpenGL ES 3.10 Shading | |

Language (March 17, 2014) Specification. | |

Overview | |

This extension provides support for implicitly converting signed integer | |

types to unsigned types, as well as more general implicit conversion and | |

function overloading infrastructure to support new data types introduced by | |

other extensions. | |

Modifications to The OpenGL ES Shading Language Specification, Version 3.10 | |

Including the following line in a shader can be used to control the | |

language features described in this extension: | |

#extension GL_EXT_shader_implicit_conversions : <behavior> | |

where <behavior> is as specified in section 3.4. | |

A new preprocessor #define is added to the OpenGL ES Shading Language: | |

#define GL_EXT_shader_implicit_conversions 1 | |

Add new section 4.1.10 following section 4.1.9 "Arrays": | |

4.1.10 Implicit Conversions | |

In some situations, an expression and its type will be implicitly | |

converted to a different type. The following table shows all allowed | |

implicit conversions: | |

Can be implicitly | |

Type of expression converted to | |

--------------------- ----------------- | |

int uint, float | |

ivec2 uvec2, vec2 | |

ivec3 uvec3, vec3 | |

ivec4 uvec4, vec4 | |

uint float | |

uvec2 vec2 | |

uvec3 vec3 | |

uvec4 vec4 | |

No implicit conversions are provided to convert from unsigned to signed | |

integer types or from floating-point to integer types. There are no | |

implicit array or structure conversions. | |

When an implicit conversion is done, it is not a re-interpretation of | |

the expression's bit pattern, but a conversion of its value to an | |

equivalent value in the new type. For example, the integer value -5 will | |

be converted to the floating-point value -5.0. Integer values having | |

more bits of precision than a single-precision floating-point mantissa | |

will lose precision when converted to float. | |

When performing implicit conversion for binary operators, there may be | |

multiple data types to which the two operands can be converted. For | |

example, when adding an int value to a uint value, both values can be | |

implicitly converted to uint and float. In such cases, a floating-point | |

type is chosen if either operand has a floating-point type. Otherwise, | |

an unsigned integer type is chosen if either operand has an unsigned | |

integer type. Otherwise, a signed integer type is chosen. If operands | |

can be implicitly converted to multiple data types deriving from the | |

same base data type, the type with the smallest component size is used. | |

The conversions in the table above are done only as indicated by other | |

sections of this specification. | |

Modify Section 5.9 "Expressions", p. 81: | |

(modify the specified items in the bulleted list as follows, adding | |

support for implicit conversion between signed and unsigned types) | |

Expressions in the shading language are built from the following: | |

* The arithmetic binary operators add (+), subtract (-), multiply (*), | |

and divide (/) operate on integer an floating-point scalars, vectors, | |

and matrices. If the fundamental types in the operands do not match, | |

then the conversions from section 4.1.10 "Implicit Conversions" are | |

applied to create matching types. All arithmetic binary operators ... | |

* The operator modulus (%) operates on signed or unsigned integer | |

scalars or integer vectors. If the fundamental types of the operands | |

do not match, the conversions from Section &4.1.10 "Implicit | |

Conversions" are applied to produce matching types. The operands | |

cannot be vectors of differing size ... | |

* The relational operators greater than (>), less than (<), greater than | |

or equal (>=), and less than or equal (<=) operate only on scalar | |

integer and scalar floating-point expressions. The result is scalar | |

Boolean. Either the operands' types must match, or the conversions | |

from section 4.1.10 "Implicit Conversions" will be applied to obtain | |

matching types. To do component-wise relational comparisons ... | |

* The equality operators equal (==), and not equal (!=) operate on all | |

types. They result in a scalar Boolean. If the operand types do not | |

match, then there must be a conversion from section 4.1.10 "Implicit | |

Conversions" applied to one operand that can make them match, in which | |

case this conversion is done. For vectors, matrices, structures, ... | |

* The ternary selection operator (?:). It operates on three expressions | |

(exp1 ? exp2 : exp3). This operator evaluates the first expression, | |

which must result in a scalar Boolean. If the result is true, it | |

selects to evaluate the second expression, otherwise it selects to | |

evaluate the third expression. Only one of the second and third | |

expressions is evaluated. The second and third expressions can be any | |

type, as long their types match, or there is a conversion in section | |

4.1.10 "Implicit Conversions" that can be applied to one of the | |

expressions to make their types match. This resulting matching type is | |

the type of the entire expression. | |

Modify Section 6.1, Function Definitions, p. 88 | |

(modify description of overloading) | |

Function names can be overloaded. The same function name can be used for | |

multiple functions, as long as the parameter types differ. If a function | |

name is declared twice with the same parameter types, then the return | |

types and all qualifiers must also match, and it is the same function | |

being declared. For example, | |

vec4 f(in vec4 x, out vec4 y); // (A) | |

vec4 f(in vec4 x, out uvec4 y); // (B) okay, different argument type | |

vec4 f(in ivec4 x, out uvec4 y); // (C) okay, different argument type | |

int f(in vec4 x, out ivec4 y); // error, only return type differs | |

vec4 f(in vec4 x, in vec4 y); // error, only qualifier differs | |

vec4 f(const in vec4 x, out vec4 y); // error, only qualifier differs | |

When function calls are resolved, an exact type match for all the | |

arguments is sought. If an exact match is found, all other functions are | |

ignored, and the exact match is used. If no exact match is found, then | |

the implicit conversions in section 4.1.10 (Implicit Conversions) will | |

be applied to find a match. Mismatched types on input parameters ("in" | |

or default) must have a conversion from the calling argument type to the | |

formal parameter type. Mismatched types on output parameters ("out") | |

must have a conversion from the formal parameter type to the calling | |

argument type. | |

If implicit conversions can be used to find more than one matching | |

function, a single best-matching function is sought. To determine a best | |

match, the conversions between calling argument and formal parameter | |

types are compared for each function argument and pair of matching | |

functions. After these comparisons are performed, each pair of matching | |

functions are compared. A function definition A is considered a better | |

match than function definition B if: | |

* for at least one function argument, the conversion for that argument | |

in A is better than the corresponding conversion in B; and | |

* there is no function argument for which the conversion in B is | |

better than the corresponding conversion in A. | |

If a single function definition is considered a better match than every | |

other matching function definition, it will be used. Otherwise, a | |

compile-time semantic error for an ambiguous overloaded function call | |

occurs. | |

To determine whether the conversion for a single argument in one match | |

is better than that for another match, the rule that an exact match is | |

better than a match involving any implicit conversion is used. | |

If this rule does not apply to a particular pair of conversions, | |

neither conversion is considered better than the other. | |

For the function prototypes (A), (B), and (C) above, the following | |

examples show how the rules apply to different sets of calling argument | |

types: | |

f(vec4, vec4); // exact match of vec4 f(in vec4 x, out vec4 y) | |

f(vec4, uvec4); // exact match of vec4 f(in vec4 x, out ivec4 y) | |

f(ivec4, vec4); // NOT matched. All three match by implicit | |

// conversion. (C) is better than (A) and (B) | |

// on the first argument. (A) is better than | |

// (B) and (C). | |

User-defined functions can have multiple ... | |

New Implementation Dependent State | |

None. | |

Issues | |

Note: These issues apply specifically to the definition of the | |

EXT_shader_implicit_conversions specification, which is based on the | |

OpenGL extension ARB_gpu_shader5 as updated in OpenGL 4.x. Resolved issues | |

from ARB_gpu_shader5 have been removed, but some remain applicable to this | |

extension. ARB_gpu_shader5 can be found in the OpenGL Registry. | |

(1) What functionality was removed relative to ARB_gpu_shader5? | |

- everything unrelated to implicit conversions and function overloading. | |

- Interactions with features not supported by the underlying | |

ES 3.1 API and Shading Language, including: | |

* interactions with ARB_gpu_shader_fp64 and NV_gpu_shader, including | |

support for double-precision in implicit conversions and function | |

overload resolution | |

* shading language function overloading rules involving the type | |

double | |

(2) What functionality was changed and added relative to | |

ARB_gpu_shader5? | |

None. | |

(3) Are the function overloading rules and examples correct? | |

RESOLVED. Rules 2 and 3 as given in the GLSL 4.40 specification do not | |

apply to ESSL, because there are no double types. There is a bug in the | |

example | |

f(vec4, ivec4); // matched to vec4 f(in vec4 x, out vec4 y) | |

// (A) better than (B) for 2nd argument | |

// argument (rule 2), same on first argument. | |

both because this example is incorrect WRT the overloading rules | |

starting with GLSL 4.00.4, and because the overloading rules in ESSL are | |

simpler. This example has been removed (see bug 11178). | |

Revision History | |

Revision 1, 2013/11/20 (Daniel Koch) | |

- Initial version extracted from EXT_gpu_shader5 rev 2. | |

Revision 2, 2013/11/21 (Jon Leech) | |

- Resolve function overloading issue 7, per bug 11178. | |

Revision 3, 2013/12/18 (Daniel Koch) | |

- minor cleanup | |

Revision 4, 2014/03/10 (Jon Leech) | |

- Rebase on OpenGL ES 3.1 and change suffix to EXT. | |

Revision 5, 2014/03/26 (Jon Leech) | |

- Sync with released ES 3.1 specs. | |

Revision 6, 2014/04/01 (Daniel Koch) | |

- update contributors |