api(ImageBuf): IB::localpixels_as_[writable_]byte_image_span

[lgritz]

Utilities to ask the IB for the local pixels as an untyped span of bytes. This is a "safe" alternative to localpixels(), which just returned a single pointer, instead returning an image_span that understands the sizes and strides of the buffer.

[lgritz]

Note: the bleeding edge test failure is not from this PR, it's due to a new commit in main of pybind11 that is causing things to crash. I have reported it.

[lgritz]

Any comments?

[EmilDohne]

[consider] It may be clearer to indicate that the return of this can be inferred from ImageBuf::storage. So for example:

Return an .. if ImageBuf::storage() is Storage::MEMORY`, otherwise ...

Apokogies if I botched that ayntax but hopefully the intention comes across

[lgritz]

I think I'm going to keep it as-is, because the storage test is actually a little more complicated than that. There are multiple storage() types that have addressable pixels, and multiple (at some point in the future, if not now) that do not. So I think keeping vague "if they are fully in RAM" is the distinction I'm trying to make.

[Copilot]

Pull request overview

This PR adds new utility methods to the ImageBuf class that provide safer access to local pixel data by returning image_span objects instead of raw pointers. This allows callers to work with pixel memory while maintaining information about buffer sizes and strides.

Changes:

• Added two new methods to return local pixels as byte image spans: one for read-only access and one for writable access
• The writable variant includes a check to return an empty span for read-only ImageBuf instances

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/libOpenImageIO/imagebuf.cpp	Implementation of the two new methods that return image spans wrapping the internal buffer
src/include/OpenImageIO/imagebuf.h	Public API declarations with documentation for the new localpixels_as_byte_image_span methods

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[Copilot]

The method is declared as const but returns a writable image_span<std::byte>, which allows modification of the underlying buffer. This violates const-correctness. Consider removing the const qualifier from this method, as it provides mutable access to the ImageBuf's data.

Suggested change

	ImageBuf::localpixels_as_writable_byte_image_span() const
	ImageBuf::localpixels_as_writable_byte_image_span()