commit 3c20b6127e96f26e3019e6c7d2a1138f651d4af1
author Corentin Wallez <cwallez@chromium.org> Wed Oct 01 07:14:48 2025 -0700
committer Dawn LUCI CQ <dawn-scoped@luci-project-accounts.iam.gserviceaccount.com> Wed Oct 01 07:14:48 2025 -0700
tree 488771f3f6a060a6761d2adcdcda63aacea8ff59
parent 8e0def799cd5743e818502ea509be0277c895e23

[dawn][native] Store ExternalTexture in BGL BindingInfo

Store both internal bindings and external bindings in the BGL. This is
the new comment at the top of the class that explains the newly added
APIBindingIndex as well.

<copypaste>
BindGroupLayout stores the information passed in the BindGroupLayoutDescriptor
but processes it in various ways to make it more efficient to use internally
and to add internal bindings used to implement WebGPU feature that don't exist
in backend APIs.

Storing information in hashmap<BindingNumber, T> would be inefficient because
these numbers may be sparse. Instead the are compacted into vectors, and
reordered using |BindingTypeOrder| to make it efficient to iterate over all the
bindings of a same kind. Indexind the packed bindings is done with
|BindingIndex| or |APIBindingIndex| (see below for the explanation).

In other cases bindings need to be expanded because a single BGLEntry can
match multiple BGEntries when bindingArraySize > 1. To make handling more
regular, a fake BGLEntry is created for each array element such that most code
doesn't need to be aware of bindingArraySize.

We also need to have private bindings that cannot be set by the users: dynamic
binding array or ExternalTextures add additional bindings for their inner
workings which are private to Dawn. Conversely ExternalTexture is a pure
frontend object and doesn't exist in backends, so dawn::native must mostly be
unaware about it. This is where |BindingIndex| and |APIBindingIndex| are
different:

 - |APIBindingIndex| are user-facing bindings and cannot be used to access
 private bindings. It is used in code for BindGroup validation and opertations
 and when reflecting/validating WGSL bind points.
 - |BindingIndex| are Dawn-facing bindings where ExternalTexture shouldn't be
 accessed and instead can be used to access internal bindings.

Internally both |APIBindingIndex| and |BindingIndex| are used to access the
same vector, but the types are used to force uses of different BindGroupLayout
accessors that ASSERT the invariant above.
</copypaste>

ShaderModule in every backend is modified to iterate over the BGL's
BindingInfo using the BindingMap. Previously they iterated over the list
of bindings in the EntryPointMetadata. Iterating over the BGL's entries
allow using the new ExternalTextureBindingInfo that points at the
BindingIndex of its plane0/1/metadata, but requires converting from
APIBindingIndex to BindingIndex. (in future CLs the GenerateBindings can
be factored between all the backends)

The OpenGL ShaderModule is modified further to use a BindingIndex
instead of a BindingNumber in the CombinedSamplerPair.

A few additional cleanups will be done in follow-up CLs:
 - The external texture expansion map will be removed.
 - BGL::GetBindingIndex(BindingNumber) will be removed.

Bug: 42240282
Change-Id: I745d6dcaa1368be2656e09525e77edd0a34709bb
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/262196
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Auto-Submit: Corentin Wallez <cwallez@chromium.org>