Fix correct bindings for bindless resource model [SPIRV and GLSL] (#7131)

Fix correct bindings for bindless resource model [spirv and glsl]

fixes: #6952

Problem:
* Currently all bindless objects are placed in the same set (fine) and same binding (incorrect behavior for vulkan). This is incorrect since as per [spec](https://registry.khronos.org/vulkan/specs/latest/man/html/VkDescriptorType.html), only 1 resource type may be written to each index inside a set (these rules are loosened with VK_EXT_mutable_descriptor_type)
* This means currently generated bindings do not work in practice if we (for example) use `Sampler2D.Handle` and `Texture1D.Handle` in a shader since we would place 2 incompatible objects in the same binding-index and set.

Solution:
* `__getDynamicResourceHeap` was modified to allow bindings to chosen dynamically for a descriptor
* use `IOpaqueDescriptor` to check compile-time information of resource types so that we can identify different resources
* Using this information of `IOpaqueDescriptor`, we modify `defaultGetDescriptorFromHandle` to provide a binding model (1 resource per binding-index) which produces legal spirv/glsl.
* To support `VK_EXT_mutable_descriptor_type` the function `defaultGetDescriptorFromHandle` has a set of options (`BindlessDescriptorOptions`) for a user to pick-from to support their binding model. Capabilities are not used here for flexibility purposes (specifically old shaders mixed with modern vulkan extensions).

Other changes:
* Added `TexelBuffer` DescriptorKind to aid in generating correct bindings

* format code

* Add to docs bindless changes, make AccelerationStructure use its handle directly, adjust tests accordingly

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

1 files changed, 47 insertions, 2 deletions

diff --git a/docs/user-guide/03-convenience-features.md b/docs/user-guide/03-convenience-features.md
index 1e9a79882..2c2eb6f42 100644
--- a/docs/user-guide/03-convenience-features.md
+++ b/docs/user-guide/03-convenience-features.md
@@ -604,6 +604,24 @@ When targeting SPIRV, Slang will introduce a global array of descriptors and fet
 The descriptor set ID of the global descriptor array can be configured with the `-bindless-space-index`
 (or `CompilerOptionName::BindlessSpaceIndex` when using the API) option.
 
+Default behavior assigns the following binding-indicies to each descriptor type:
+```slang
+enum DefaultVkBindlessBindings : uint
+{
+    Sampler = 0, /// SAMPLER
+    CombinedTextureSampler = 1, /// COMBINED_IMAGE_SAMPLER
+    Texture_Read = 2, /// SAMPLED_IMAGE
+    Texture_ReadWrite = 3, /// STORAGE_IMAGE
+    TexelBuffer_Read = 4, /// UNIFORM_TEXEL_BUFFER
+    TexelBuffer_ReadWrite = 5, /// STORAGE_TEXEL_BUFFER
+    Buffer_Read = 6, /// UNIFORM_BUFFER
+    Buffer_ReadWrite = 7, /// STORAGE_BUFFER
+    Unknown = 8, /// Other
+}
+``` 
+
+`ACCELERATION_STRUCTURE` is excluded from the list of types since slang by default uses the provided handle to a `RaytracingAccelerationStructure` as a GPU address into the respective `RaytracingAccelerationStructure`, casting the 64bit handle into the type.
+
 > #### Note
 > The default implementation for SPIRV may change in the future if SPIRV is extended to provide what is
 > equivalent to D3D's `ResourceDescriptorHeap` construct.
@@ -653,8 +671,32 @@ interface IOpaqueDescriptor
 The user can call `defaultGetDescriptorFromHandle` function from their implementation of
 `getDescriptorFromHandle` to dispatch to the default behavior.
 
-The `kind` and `descriptorAccess` constants allows user code to fetch from different locations
-depending on the type and access of the resource being requested. The `DescriptorKind` and
+Additionally, `defaultGetDescriptorFromHandle` has the parameter `constexpr BindlessDescriptorOptions bindlessOptions`. This parameter provides some alternative presets for how bindless indexes are assigned (currently only relevant to SPIRV):
+ ```slang
+public enum BindlessDescriptorOptions
+{
+    None = 0, /// Bind assuming regular binding model rules.
+    VkMutable = 1, /// Bind assuming `VK_EXT_mutable_descriptor_type` without mutable `AccelerationStructure` binding support.
+}
+ ```
+
+`VkMutable` provides the following bindings for descriptor types:
+```slang
+enum VkMutableBindlessBindings : uint
+{
+    Sampler = 0, /// SAMPLER
+    CombinedTextureSampler = 1, /// COMBINED_IMAGE_SAMPLER
+    Texture_Read = 2, /// SAMPLED_IMAGE
+    Texture_ReadWrite = 2, /// STORAGE_IMAGE
+    TexelBuffer_Read = 2, /// UNIFORM_TEXEL_BUFFER
+    TexelBuffer_ReadWrite = 2, /// STORAGE_TEXEL_BUFFER
+    Buffer_Read = 2, /// UNIFORM_BUFFER
+    Buffer_ReadWrite = 2, /// STORAGE_BUFFER,
+    Unknown = 3, /// Other
+}
+```
+
+The `kind` and `descriptorAccess` constants allows user code to fetch resources from different locations depending on the type and access of the resource being requested. The `DescriptorKind` and
 `DescriptorAccess` enums are defined as:
 
 ```slang
@@ -666,6 +708,7 @@ enum DescriptorKind
     Buffer, /// A buffer descriptor.
     Sampler, /// A sampler state descriptor.
     AccelerationStructure, /// A ray tracing acceleration structure descriptor.
+    TexelBuffer /// A texel buffer descriptor.
 }
 
 enum DescriptorAccess
@@ -692,6 +735,8 @@ void test(DescriptorHandle<Texture2D> t)
 If the resource pointer value is not uniform and `nonuniform` is not called, the result may be
 undefined.
 
+
+
 Extensions
 --------------------
 Slang allows defining additional methods for a type outside its initial definition. For example, suppose we already have a type defined: