SPIR-V Extension SPV_AMD_texture_gather_bias_lod

SPV_AMD_texture_gather_bias_lod

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

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

Proposed.

Modified Date: June 22, 2017 Revision: 2

This extension is written against Revision 4 of the version 1.1 of the SPIR-V Specification.

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

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.

To enable SPV_AMD_texture_gather_bias_lod extension in SPIR-V, use

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.

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:

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.