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[SPIR-V] Explicitly state which layout rules require scalar block layout #7539

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s-perron merged 3 commits into from
Jul 3, 2025
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[SPIR-V] Explicitly state which layout rules require scalar block layout #7539

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[SPIR-V] Explicitly state which layout rules require scalar block layout
shawnhatori Jun 15, 2025
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move addition to new line
shawnhatori Jun 15, 2025
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Merge branch 'microsoft:main' into patch-1
shawnhatori Jun 23, 2025
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13 changes: 7 additions & 6 deletions docs/SPIR-V.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1012,17 +1012,18 @@ right now:
2. DirectX memory layout rules for uniform buffers and storage buffers:
they allow packing data on the application side that can be shared with
DirectX. They can be enabled by ``-fvk-use-dx-layout``.

NOTE: This requires ``VK_EXT_scalar_block_layout`` to be enabled on the
application side.
3. Strict OpenGL ``std140`` for uniform buffers and strict OpenGL ``std430``
for storage buffers: they allow packing data on the application side that
can be shared with OpenGL. They can be enabled by ``-fvk-use-gl-layout``.
4. Scalar layout rules introduced via `VK_EXT_scalar_block_layout`, which
basically aligns all aggregrate types according to their elements'
natural alignment. They can be enabled by ``-fvk-use-scalar-layout``.

To use scalar layout, the application side need to request
``VK_EXT_scalar_block_layout``. This is also true for using DirectX memory
layout since there is no dedicated DirectX layout extension for Vulkan
(at least for now). So we must request something more permissive.

NOTE: This requires ``VK_EXT_scalar_block_layout`` to be enabled on the
application side.

In the above, "vector-relaxed OpenGL ``std140``/``std430``" rules mean OpenGL
``std140``/``std430`` rules with the following modification for vector type
Expand All @@ -1032,7 +1033,7 @@ alignment:
2. If the above causes an `improper straddle <https://registry.khronos.org/vulkan/specs/latest/html/vkspec.html#interfaces-resources-layout>`_,
the alignment will be set to 16 bytes.

As an exmaple, for the following HLSL definition:
As an example, for the following HLSL definition:

.. code:: hlsl

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