[FEATURE] - Support use of ReadOnly/Span in APIs

[Clockwork-Muse]

Describe the feature
I'm writing a program that receives images from a connected device. As part of that, I'm using the new System.IO.Pipelines, which gives me some combination of;

• ReadOnly/Span
• ReadOnly/Memory
• ReadOnlySequence

Unfortunately, it's not possible to get the underlying byte array that these types use for actual backing memory (if any such exists), meaning that in order to call, say, imdecode I'm required to copy to an array for the decoding to happen.

It would be helpful if instead most of the available APIs supported passing Span types.

An additional side option here is, if OpenCV allows access, to wrap the native memory allocated by OpenCV itself, and implement the MemoryManager API.

[sn4k3]

Take a look at EmguExtensions.cs search for Span

[Clockwork-Muse]

@sn4k3 - I'm trying to call imdecode, and I start with a Span, not need one as the result of a call (at the moment).

[sn4k3]

@sn4k3 - I'm trying to call imdecode, and I start with a Span, not need one as the result of a call (at the moment).

Ok for that is required the implementation in the method.
But if you have a span you should also have the array and passing it without the need of copy your span to a new buffer?

[emgucv]

Are you trying to call Imdecode on a Span?

The Imdecode function expect a pointer to byte. I don't think you can get a pointer from Span based on the documentation:
https://learn.microsoft.com/en-us/dotnet/api/system.span-1?view=net-8.0

If you can't get a pointer from a Span, you will need to copy it to a buffer that can give you a pointer.

[Clockwork-Muse]

But if you have a span you should also have the array and passing it without the need of copy your span to a new buffer?

That might not be the case - my original code was using MemoryPool<byte> and IMemoryOwner<byte> as the more "modern" setup (as opposed to ArrayPool<byte>), so I didn't have access to the underlying array.

Are you trying to call Imdecode on a Span?

The Imdecode function expect a pointer to byte.

On a Span/ReadOnlySpan, yes.
(Or rather - I start from a ReadOnlySequence, but none of the native imdecode overloads would be able to work with an iterable set of buffers, so not expecting it to be usable here)

You can get a pointer via use of the fixed statement:

unsafe
{
    int[] numbers = [10, 20, 30, 40, 50];
    Span<int> interior = numbers.AsSpan()[1..^1];
    fixed (int* p = interior)
    {
        for (int i = 0; i < interior.Length; i++)
        {
            Console.Write(p[i]);  
        }
        // output: 203040
    }
}