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[0018] Update cbuffer representation #273

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[0018] Update cbuffer representation #273

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c8fccdb
[0018] Update cbuffer representation
s-perron May 7, 2025
fc0f4de
Fix typo
s-perron May 28, 2025
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37 changes: 24 additions & 13 deletions proposals/0018-spirv-resource-representation.md
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Original file line number Diff line number Diff line change
Expand Up @@ -66,7 +66,7 @@ type. For now, the counter variable will not be handled. We will create a target
type `spirv.VulkanBuffer` to represent a storage or uniform buffer:

```
target("spirv.VulkanBuffer", ElementType, StorageClass, IsWriteable, IsROV)
target("spirv.VulkanBuffer", ElementType, StorageClass, IsWriteable)
```

`ElementType` is the type for the storage buffer array, and `StorageClass` is
Expand Down Expand Up @@ -149,13 +149,13 @@ it is used.

The handle for structured buffers will be

| HLSL Resource Type | Handle Type |
|--------------------------------------|----------------------------------------------------|
| StructuredBuffer<T> | spirv.VulkanBuffer(T, StorageBuffer, false, false) |
| RWStructuredBuffer<T> | spirv.VulkanBuffer(T, StorageBuffer, true, false) |
| RasterizerOrderedStructuredBuffer<T> | spirv.VulkanBuffer(T, StorageBuffer, true, true) |
| AppendStructuredBuffer<T> | spirv.VulkanBuffer(T, StorageBuffer, true, false) |
| ConsumeStructuredBuffer<T> | spirv.VulkanBuffer(T, StorageBuffer, true, false) |
| HLSL Resource Type | Handle Type |
|--------------------------------------|---------------------------------------------|
| StructuredBuffer<T> | spirv.VulkanBuffer(T, StorageBuffer, false) |
| RWStructuredBuffer<T> | spirv.VulkanBuffer(T, StorageBuffer, true) |
| RasterizerOrderedStructuredBuffer<T> | TODO |
| AppendStructuredBuffer<T> | spirv.VulkanBuffer(T, StorageBuffer, true) |
| ConsumeStructuredBuffer<T> | spirv.VulkanBuffer(T, StorageBuffer, true) |

### Texture buffers

Expand All @@ -164,17 +164,28 @@ perspective, this makes it the same as a `StructureBuffer`, and will be
represented the same way:

```
spirv.VulkanBuffer(T, StorageBuffer, false, false)
spirv.VulkanBuffer(T, StorageBuffer, false)
```

### Constant buffers

In SPIR-V, constant buffers are implemented as uniform buffers. The only
difference between a uniform buffer and storage buffer is the storage class.
Uniform buffers use the `Uniform` storage class. The handle type will be:
Our design for constant buffers will be in line with
proposal [0016 constant buffers](0016-constant-buffers.md).
As in that proposal, we will use `spirv.LayoutType` for the struct in the
buffer. We use the layout type
because we cannot reorder or add new members to the layout type to allow the
standard offset calculations for structs to work. That will break the `hlsl.cbs`
metadata.

TODO: Still unclear how to lay out the members of `T` that are structs.

The `spirv.Layout` will then be wrapped in a `spirv.VulkanBuffer` type to
represent a uniform buffer:

The handle type will be:

```
spirv.VulkanBuffer(T, Uniform, false, false)
spirv.VulkanBuffer(spirv.LayoutType(T, sizeof(T), Offsets...), Uniform, false)
```

### Samplers
Expand Down