[llvm] [DirectX] Documenting Root Signature Binary representation (PR #131011)

[via llvm-commits]

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@@ -400,3 +400,258 @@ SFI0 Part
 The SFI0 part encodes a 64-bit unsigned integer bitmask of the feature flags.
 This denotes which optional features the shader requires. The flag values are
 defined in `llvm/include/llvm/BinaryFormat/DXContainerConstants.def <https://github.com/llvm/llvm-project/blob/main/llvm/include/llvm/BinaryFormat/DXContainerConstants.def>`_.
+
+Root Signature (RTS0) Part
+--------------------------
+.. _RTS0:
+
+The Root Signature defines the interface between the shader and the pipeline, 
+specifying which resources are bound to the shader and how they are accessed. 
+This structure serves as a contract between the application and the GPU, 
+establishing a layout for resource binding that both the shader compiler and 
+the runtime can understand.
+
+The Root Signature consists of a header followed by a collection of root parameters 
+and static samplers. The structure uses a versioned design with offset-based references 
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joaosaffran wrote:

That is the usual pattern I've followed, but it is not necessarily always the case. Root Parameters and static samplers definitions are located using an offset with relation to the start of the RTS0 part. That mean that there is no strict order between parameters and static samplers. The only rule is that they should be after the root signature header.

https://github.com/llvm/llvm-project/pull/131011