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@@ -590,31 +590,39 @@ Firstly, under certain `SigPoints <https://github.com/Microsoft/DirectXShaderCom
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some system-value (SV) semantic strings will be translated into SPIR-V
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``BuiltIn`` decorations:
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-+----------------------+----------+--------------------------+-----------------------+
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-| HLSL Semantic | SigPoint | SPIR-V ``BuiltIn`` | SPIR-V Execution Mode |
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-+======================+==========+==========================+=======================+
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-| | VSOut | ``Position`` | N/A |
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-| SV_Position +----------+--------------------------+-----------------------+
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-| | PSIn | ``FragCoord`` | N/A |
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-+----------------------+----------+--------------------------+-----------------------+
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-| SV_VertexID | VSIn | ``VertexIndex`` | N/A |
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-+----------------------+----------+--------------------------+-----------------------+
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-| SV_InstanceID | VSIn | ``InstanceIndex`` | N/A |
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-+----------------------+----------+--------------------------+-----------------------+
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-| SV_Depth | PSOut | ``FragDepth`` | N/A |
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-+----------------------+----------+--------------------------+-----------------------+
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-| SV_DepthGreaterEqual | PSOut | ``FragDepth`` | ``DepthGreater`` |
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-+----------------------+----------+--------------------------+-----------------------+
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-| SV_DepthLessEqual | PSOut | ``FragDepth`` | ``DepthLess`` |
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-+----------------------+----------+--------------------------+-----------------------+
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-| SV_DispatchThreadID | CSIn | ``GlobalInvocationId`` | N/A |
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-+----------------------+----------+--------------------------+-----------------------+
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-| SV_GroupID | CSIn | ``WorkgroupId`` | N/A |
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-+----------------------+----------+--------------------------+-----------------------+
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-| SV_GroupThreadID | CSIn | ``LocalInvocationId`` | N/A |
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-+----------------------+----------+--------------------------+-----------------------+
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-| SV_GroupIndex | CSIn | ``LocalInvocationIndex`` | N/A |
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-+----------------------+----------+--------------------------+-----------------------+
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++-------------------------+-------------+--------------------------+-----------------------+
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+| HLSL Semantic | SigPoint | SPIR-V ``BuiltIn`` | SPIR-V Execution Mode |
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++=========================+=============+==========================+=======================+
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+| | VSOut | ``Position`` | N/A |
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+| SV_Position +-------------+--------------------------+-----------------------+
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+| | PSIn | ``FragCoord`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_VertexID | VSIn | ``VertexIndex`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_InstanceID | VSIn | ``InstanceIndex`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_Depth | PSOut | ``FragDepth`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_DepthGreaterEqual | PSOut | ``FragDepth`` | ``DepthGreater`` |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_DepthLessEqual | PSOut | ``FragDepth`` | ``DepthLess`` |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_DispatchThreadID | CSIn | ``GlobalInvocationId`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_GroupID | CSIn | ``WorkgroupId`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_GroupThreadID | CSIn | ``LocalInvocationId`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_GroupIndex | CSIn | ``LocalInvocationIndex`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_OutputControlPointID | HSIn | ``InvocationId`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_PrimitiveID | HSIn / PCIn | ``PrimitiveId`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_TessFactor | PCOut | ``TessLevelOuter`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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+| SV_InsideTessFactor | PCOut | ``TessLevelInner`` | N/A |
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++-------------------------+-------------+--------------------------+-----------------------+
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[TODO] add other SV semantic strings in the above
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@@ -1640,3 +1648,88 @@ element is the height, and the third is the elements.
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++++++++++++++++++++++++++++++++++++++++
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The ``OpImageQuerySize`` instruction is used to get a uint3. The first element is the width, the second
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element is the height, and the third element is the depth.
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+
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+
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+HLSL Hull Shaders
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+=================
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+
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+Hull shaders corresponds to Tessellation Control Shaders (TCS) in Vulkan.
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+This section describes how Hull shaders are translated to SPIR-V for Vulkan.
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+
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+Hull Entry Point Attributes
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+---------------------------
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+The following HLSL attributes are attached to the main entry point of hull shaders
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+and are translated to SPIR-V execution modes according to the table below:
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+
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++-------------------------+---------------------+--------------------------+
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+| HLSL Attribute | value | SPIR-V Execution Mode |
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++=========================+=====================+==========================+
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+| | ``quad`` | ``Quads`` |
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+| +---------------------+--------------------------+
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+| ``domain`` | ``tri`` | ``Triangles`` |
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+| +---------------------+--------------------------+
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+| | ``isoline`` | ``Isoline`` |
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++-------------------------+---------------------+--------------------------+
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+| | ``integer`` | ``SpacingEqual`` |
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+| +---------------------+--------------------------+
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+| | ``fractional_even`` | ``SpacingFractionalEven``|
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+| ``partitioning`` +---------------------+--------------------------+
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+| | ``fractional_odd`` | ``SpacingFractionalOdd`` |
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+| +---------------------+--------------------------+
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+| | ``pow2`` | N/A |
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++-------------------------+---------------------+--------------------------+
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+| | ``point`` | ``PointMode`` |
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+| +---------------------+--------------------------+
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+| | ``line`` | N/A |
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+| ``outputtopology`` +---------------------+--------------------------+
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+| | ``triangle_cw`` | ``VertexOrderCw`` |
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+| +---------------------+--------------------------+
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+| | ``triangle_ccw`` | ``VertexOrderCcw`` |
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++-------------------------+---------------------+--------------------------+
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+|``outputcontrolpoints`` | ``n`` | ``OutputVertices n`` |
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++-------------------------+---------------------+--------------------------+
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+
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+The ``patchconstfunc`` attribute does not have a direct equivalent in SPIR-V.
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+It specifies the name of the Patch Constant Function. This function is run only
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+once per patch. This is further described below.
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+
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+InputPatch and OutputPatch
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+--------------------------
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+Both of ``InputPatch<T, N>`` and ``OutputPatch<T, N>`` are translated to an array
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+of constant size ``N`` where each element is of type ``T``.
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+
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+InputPatch can be passed to the Hull shader main entry function as well as the
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+patch constant function. This would include information about each of the ``N``
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+vertices that are input to the tessellation control shader.
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+
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+OutputPatch is an array containing ``N`` elements (where ``N`` is the number of
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+output vertices). Each element of the array contains information about an
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+output vertex. OutputPatch may also be passed to the patch constant function.
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+
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+The SPIR-V ``InvocationID`` (``SV_OutputControlPointID`` in HLSL) is used to index
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+into the InputPatch and OutputPatch arrays to read/write information for the given
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+vertex.
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+
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+The hull main entry function in HLSL returns only one value (say, of type ``T``), but
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+that function is in fact executed once for each control point. The Vulkan spec requires that
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+"Tessellation control shader per-vertex output variables and blocks, and tessellation control,
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+tessellation evaluation, and geometry shader per-vertex input variables and blocks are required
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+to be declared as arrays, with each element representing input or output values for a single vertex
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+of a multi-vertex primitive". Therefore, we need to create a stage output variable that is an array
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+with elements of type ``T``. The number of elements of the array is equal to the number of
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+output control points. Each final output control point is written into the corresponding element in
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+the array using SV_OutputControlPointID as the index.
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+
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+Patch Constant Function
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+-----------------------
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+As mentioned above, the patch constant function is to be invoked only once per patch.
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+As a result, in the SPIR-V module, the `entry function wrapper`_ will first invoke the
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+main entry function, and then use an ``OpControlBarrier`` to wait for all vertex
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+processing to finish. After the barrier, *only* the first thread (with InvocationID of 0)
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+will invoke the patch constant function.
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+
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+The information resulting from the patch constant function will also be returned
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+as stage output variables. The output struct of the patch constant function must include
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+``SV_TessFactor`` and ``SV_InsideTessFactor`` fields which will translate to
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+``TessLevelOuter`` and ``TessLevelInner`` builtin variables, respectively. And the rest
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+will be flattened and translated into normal stage output variables, one for each field.
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Ehsan