// Copyright (c) 2015-2016 The Khronos Group Inc.
// Copyright notice at https://www.khronos.org/registry/speccopyright.html

[appendix]
[[spirvenv]]
= Vulkan Environment for SPIR-V

Shaders for Vulkan are defined by the <<Khronos SPIR-V Specification>> as
well as the <<Khronos SPIR-V Extended Instructions for GLSL Specification>>.
This appendix defines additional SPIR-V requirements applying to Vulkan
shaders.

== Required Versions and Formats

A Vulkan 1.0 implementation must: support the 1.0 version of SPIR-V and
the 1.0 version of the SPIR-V Extended Instructions for GLSL.

A SPIR-V module passed into flink:vkCreateShaderModule is interpreted as
a series of 32-bit words in host endianness, with literal strings packed
as described in section 2.2 of the SPIR-V Specification. The first few words
of the SPIR-V module must: be a magic number and a SPIR-V version number, as
described in section 2.3 of the SPIR-V Specification.


[[spirvenv-capabilities]]
== Capabilities

Implementations must: support the following capability operands declared by
code:OpCapability:

  - code:Matrix
  - code:Shader
  - code:InputAttachment
  - code:Sampled1D
  - code:Image1D
  - code:SampledBuffer
  - code:ImageBuffer
  - code:ImageQuery
  - code:DerivativeControl

Implementations may: support features that are not required: by the
Specification, as described in the <<features-features,Features>> chapter.
If such a feature is supported, then any capability operand(s) corresponding
to that feature must: also be supported.

[[spirvenv-capabilities-table]]
.SPIR-V Capabilities which are not required:, and corresponding feature names
[options="header"]
|====
| SPIR-V OpCapability                     | Vulkan feature name
| code:Geometry                           | <<features-features-geometryShader,geometryShader>>
| code:Tessellation                       | <<features-features-tessellationShader,tessellationShader>>
| code:Float64                            | <<features-features-shaderFloat64,shaderFloat64>>
| code:Int64                              | <<features-features-shaderInt64,shaderInt64>>
| code:Int16                              | <<features-features-shaderInt16,shaderInt16>>
| code:TessellationPointSize              | <<features-features-shaderTessellationAndGeometryPointSize,shaderTessellationAndGeometryPointSize>>
| code:GeometryPointSize                  | <<features-features-shaderTessellationAndGeometryPointSize,shaderTessellationAndGeometryPointSize>>
| code:ImageGatherExtended                | <<features-features-shaderImageGatherExtended,shaderImageGatherExtended>>
| code:StorageImageMultisample            | <<features-features-shaderStorageImageMultisample,shaderStorageImageMultisample>>
| code:UniformBufferArrayDynamicIndexing  | <<features-features-shaderUniformBufferArrayDynamicIndexing,shaderUniformBufferArrayDynamicIndexing>>
| code:SampledImageArrayDynamicIndexing   | <<features-features-shaderSampledImageArrayDynamicIndexing,shaderSampledImageArrayDynamicIndexing>>
| code:StorageBufferArrayDynamicIndexing  | <<features-features-shaderStorageBufferArrayDynamicIndexing,shaderStorageBufferArrayDynamicIndexing>>
| code:StorageImageArrayDynamicIndexing   | <<features-features-shaderStorageImageArrayDynamicIndexing,shaderStorageImageArrayDynamicIndexing>>
| code:ClipDistance                       | <<features-features-shaderClipDistance,shaderClipDistance>>
| code:CullDistance                       | <<features-features-shaderCullDistance,shaderCullDistance>>
| code:ImageCubeArray                     | <<features-features-imageCubeArray,imageCubeArray>>
| code:SampleRateShading                  | <<features-features-sampleRateShading,sampleRateShading>>
| code:SparseResidency                    | <<features-features-shaderResourceResidency,shaderResourceResidency>>
| code:MinLod                             | <<features-features-shaderResourceMinLod,shaderResourceMinLod>>
| code:SampledCubeArray                   | <<features-features-imageCubeArray,imageCubeArray>>
| code:ImageMSArray                       | <<features-features-shaderStorageImageMultisample,shaderStorageImageMultisample>>
| code:StorageImageExtendedFormats        | <<features-features-shaderStorageImageExtendedFormats,shaderStorageImageExtendedFormats>>
| code:InterpolationFunction              | <<features-features-sampleRateShading,sampleRateShading>>
| code:StorageImageReadWithoutFormat      | <<features-features-shaderStorageImageReadWithoutFormat,shaderStorageImageReadWithoutFormat>>
| code:StorageImageWriteWithoutFormat     | <<features-features-shaderStorageImageWriteWithoutFormat,shaderStorageImageWriteWithoutFormat>>
| code:MultiViewport                      | <<features-features-multiViewport,multiViewport>>
|====

The application mustnot: pass a SPIR-V module containing any of the
following to flink:vkCreateShaderModule:

  - any OpCapability not listed above,
  - an unsupported capability, or
  - a capability which corresponds to a Vulkan feature which has not been
    enabled.


[[spirvenv-module-validation]]
== Validation Rules within a Module

A SPIR-V module passed to flink:vkCreateShaderModule must: conform to the
following rules:

  * Every entry point must: have no return value and accept no arguments.
  * The *Logical* addressing model must: be selected.
  * *Scope* for execution must: be limited to:
  ** *Workgroup*
  ** *Subgroup*
  * *Scope* for memory must: be limited to:
  ** *Device*
  ** *Workgroup*
  ** *Invocation*
  * The code:OriginLowerLeft execution mode mustnot: be used; fragment entry
    points must: declare code:OriginUpperLeft.
  * The code:PixelCenterInteger execution mode mustnot: be used. Pixels are
    always centered at half-integer coordinates.
  * Images
  ** code:OpTypeImage must: declare a scalar 32-bit float or 32-bit integer
     type for the ``Sampled Type''. (code:RelaxedPrecision can: be applied
     to a sampling instruction and to the variable holding the result of a
     sampling instruction.)
  ** code:OpSampledImage must: only consume an ``Image'' operand whose type
     has its ``Sampled'' operand set to 1.
  ** The ``(u, v)'' coordinates used for a code:SubpassData must: be the <id>
     of a constant vector (0, 0), or if a layer coordinate is used, must: be
     a vector that was formed with constant 0 for the ``u'' and ``v''
     components.
  ** The ``Depth'' operand of code:OpTypeImage is ignored.
  * Decorations
  ** The code:GLSLShared and code:GLSLPacked decorations mustnot: be used.
  ** The code:Flat, code:NoPerspective, code:Sample, and code:Centroid
     decorations mustnot: be used on variables with storage class other than
     code:Input or on variables used in the interface of non-fragment shader
     entry points.
  ** The code:Patch decoration mustnot: be used on variables in the
     interface of a vertex, geometry, or fragment shader stage's entry
     point.
  * code:OpTypeRuntimeArray must: only be used for the last member of an
    code:OpTypeStruct in the code:Uniform storage class.
  * Linkage: See <<interfaces,Shader Interfaces>> for additional linking and
    validation rules.
  * Compute Shaders
  ** For each compute shader entry point, either a code:LocalSize execution mode
     or an object decorated with the code:WorkgroupSize decoration must: be
     specified.


[[spirvenv-precision-operation]]
== Precision and Operation of SPIR-V Instructions

The following rules apply to both single and double-precision floating point
instructions:

  - Positive and negative infinities and positive and negative zeros are
    generated as dictated by <<IEEE 754>>, but subject to the precisions
    allowed in the following table.
  - Dividing a non-zero by a zero results in the appropriately signed <<IEEE
    754>> infinity.
  - Any denormalized value input into a shader or potentially generated by
    any instruction in a shader may: be flushed to 0.
  - The rounding mode cannot: be set and is undefined.
  - NaNs may: not be generated. Instructions that operate on a NaN may: not
    result in a NaN.
  - Support for signaling NaNs is optional: and exceptions are never raised.

The precision of double-precision instructions is at least that of single
precision. For single precision (32 bit) instructions, precisions are
required: to be at least as follows, unless decorated with RelaxedPrecision:

.Precision of core SPIR-V Instructions
[options="header"]
|====
| Instruction                                               | Precision
| code:OpFAdd                                               | Correctly rounded.
| code:OpFSub                                               | Correctly rounded.
| code:OpFMul                                               | Correctly rounded.
| code:OpFOrdEqual, code:OpFUnordEqual                      | Correct result.
| code:OpFOrdLessThan, code:OpFUnordLessThan                | Correct result.
| code:OpFOrdGreaterThan, code:OpFUnordGreaterThan          | Correct result.
| code:OpFOrdLessThanEqual, code:OpFUnordLessThanEqual      | Correct result.
| code:OpFOrdGreaterThanEqual, code:OpFUnordGreaterThanEqual| Correct result.
| code:OpFDiv                                               | 2.5 ULP for b in the range [2^-126^, 2^126^].
| conversions between types                                 | Correctly rounded.
|====

Precision of GLSL.std.450 Instructions
[options="header"]
|====
|Instruction                 | Precision
| code:fma()                 | Inherited from code:OpFMul followed by code:OpFAdd.
| code:exp(x),  code:exp2(x) | latexmath:[$(3 + 2 \times \|x\|)$] ULP.
| code:log(),  code:log2()   | 3 ULP outside the range [0.5, 2.0]. Absolute error < 2^-21^ inside the range [0.5, 2.0].
| code:pow(x, y)             | Inherited from code:exp2(y × code:log2(x)).
| code:sqrt()                | Inherited from 1.0 / code:inversesqrt().
| code:inversesqrt()         | 2 ULP.
|====

GLSL.std.450 extended instructions specifically defined in terms of the
above instructions inherit the above errors. GLSL.std.450 extended
instructions not listed above and not defined in terms of the above have
undefined precision. These include, for example, the trigonometric functions
and determinant.

For the code:OpSRem and code:OpSMod instructions, if either operand is
negative the result is undefined.

[NOTE]
.Note
====
While the code:OpSRem and code:OpSMod instructions are supported by the
Vulkan environment, they require non-negative values and thus do not
enable additional functionality beyond what code:OpUMod provides.
====


[[spirvenv-image-formats]]
Compatibility Between SPIR-V Image Formats And Vulkan Formats
-------------------------------------------------------------

[cols="2*", options="header"]
|===
|SPIR-V Image Format    |Vulkan Format
|code:Rgba32f           |ename:VK_FORMAT_R32G32B32A32_SFLOAT
|code:Rgba16f           |ename:VK_FORMAT_R16G16B16A16_SFLOAT
|code:R32f              |ename:VK_FORMAT_R32_SFLOAT
|code:Rgba8             |ename:VK_FORMAT_R8G8B8A8_UNORM
|code:Rgba8Snorm        |ename:VK_FORMAT_R8G8B8A8_SNORM
|code:Rg32f             |ename:VK_FORMAT_R32G32_SFLOAT
|code:Rg16f             |ename:VK_FORMAT_R16G16_SFLOAT
|code:R11fG11fB10f      |ename:VK_FORMAT_B10G11R11_UFLOAT_PACK32
|code:R16f              |ename:VK_FORMAT_R16_SFLOAT
|code:Rgba16            |ename:VK_FORMAT_R16G16B16A16_UNORM
|code:Rgb10A2           |ename:VK_FORMAT_A2B10G10R10_UNORM_PACK32
|code:Rg16              |ename:VK_FORMAT_R16G16_UNORM
|code:Rg8               |ename:VK_FORMAT_R8G8_UNORM
|code:R16               |ename:VK_FORMAT_R16_UNORM
|code:R8                |ename:VK_FORMAT_R8_UNORM
|code:Rgba16Snorm       |ename:VK_FORMAT_R16G16B16A16_SNORM
|code:Rg16Snorm         |ename:VK_FORMAT_R16G16_SNORM
|code:Rg8Snorm          |ename:VK_FORMAT_R8G8_SNORM
|code:R16Snorm          |ename:VK_FORMAT_R16_SNORM
|code:R8Snorm           |ename:VK_FORMAT_R8_SNORM
|code:Rgba32i           |ename:VK_FORMAT_R32G32B32A32_SINT
|code:Rgba16i           |ename:VK_FORMAT_R16G16B16A16_SINT
|code:Rgba8i            |ename:VK_FORMAT_R8G8B8A8_SINT
|code:R32i              |ename:VK_FORMAT_R32_SINT
|code:Rg32i             |ename:VK_FORMAT_R32G32_SINT
|code:Rg16i             |ename:VK_FORMAT_R16G16_SINT
|code:Rg8i              |ename:VK_FORMAT_R8G8_SINT
|code:R16i              |ename:VK_FORMAT_R16_SINT
|code:R8i               |ename:VK_FORMAT_R8_SINT
|code:Rgba32ui          |ename:VK_FORMAT_R32G32B32A32_UINT
|code:Rgba16ui          |ename:VK_FORMAT_R16G16B16A16_UINT
|code:Rgba8ui           |ename:VK_FORMAT_R8G8B8A8_UINT
|code:R32ui             |ename:VK_FORMAT_R32_UINT
|code:Rgb10a2ui         |ename:VK_FORMAT_A2B10G10R10_UINT_PACK32
|code:Rg32ui            |ename:VK_FORMAT_R32G32_UINT
|code:Rg16ui            |ename:VK_FORMAT_R16G16_UINT
|code:Rg8ui             |ename:VK_FORMAT_R8G8_UINT
|code:R16ui             |ename:VK_FORMAT_R16_UINT
|code:R8ui              |ename:VK_FORMAT_R8_UINT
|===