Name Strings

SPV_AMD_texture_gather_bias_lod

Contact

See Issues list in the Khronos SPIRV-Headers repository: https://github.com/KhronosGroup/SPIRV-Headers

Contributors

  • Dominik Witczak, AMD

  • Daniel Rakos, AMD

  • Graham Sellers, AMD

  • Matthäus G. Chajdas, AMD

  • Qun Lin, AMD

  • Rex Xu, AMD

  • Timothy Lottes, AMD

Notice

Copyright (c) 2016 The Khronos Group Inc. Copyright terms at http://www.khronos.org/registry/speccopyright.html

Status

Proposed.

Version

Modified Date: June 22, 2017 Revision: 2

Dependencies

This extension is written against Revision 4 of the version 1.10 of the SPIR-V Specification.

The extension is written against Revision 1 of the OpenGL extension AMD_texture_gather_bias_lod.

Overview

This extension is written to provide the functionality of the AMD_texture_gather_bias_lod, OpenGL Shading Language Specification extension, for SPIR-V.

This extension lets applications specify bias of implicit level of detail and explicit control of level of detail for texture gather operations.

Extension Name

To enable SPV_AMD_texture_gather_bias_lod extension in SPIR-V, use

OpExtension "SPV_AMD_texture_gather_bias_lod"

Summary

This extension lets applications specify a bias applied to the implicit level of detail, or the explicit level of detail to use for texture gather operations.

Token Number Assignments

CapabilityImageGatherBiasLodAMD

5009

Modifications to the SPIR-V Specification, Version 1.10

Modify Section 3.14, Image Operands

(Replace the following language, as included in the "Image Operands" section of the table for the "Bias" Image Operand:)

Only valid with implicit-lod instructions.

(with:)

Only valid with implicit-lod instructions, OpImageGather, or OpImageSparseGather.


(Replace the following language, as included in the "Image Operands" section of the table for the "Lod" Image Operand):

Only valid with implicit-lod instructions.

(with:)

Only valid with explicit-lod instructions, OpImageGather, or OpImageSparseGather.

Modify Section 3.31, Capability

Append the following Capability to the table:

Capability Depends On Enabled by Extension

ImageGatherBiasLodAMD

Uses texture gather with either bias added to the implicit level-of-detail or explicit level-of-detail.

Shader

SPV_AMD_texture_gather_bias_lod

Validation Rules

None.

Issues

1) What level-of-detail do texture gather functions use, if the extension is defined?

RESOLVED: If SPV_AMD_texture_gather_bias_lod extension is enabled, all texture gather functions (ie. the ones which do not take the extra bias argument and the ones that do) fetch texels from implicit LOD in fragment shader stage. In all other shader stages, base level is used instead.

If the extension is disabled, all texture gather functions always fetch texels from the base mip level.

Revision History

Rev Date Author Changes

2

June 22, 2017

Dominik Witczak

Typo fix (OpCapabilityImageGatherBiasLodAMD ⇒ CapabilityImageGatherBiasLodAMD)

1

February 21, 2017

Dominik Witczak

Initial revision based on AMD_texture_gather_bias_lod