Is it possible to expose the native pointer version for the ReadPixels method of the MagickImage ?

[TonyDragonlake]

Is your feature request related to a problem? Please describe

No response

Describe the solution you'd like

In my project, image data is from a camera and the sdk of it is using the native pointer. It's not possible to add the conversion from native pointer to the managed byte array due the performance requirement. So I wonder is it possible to expose the native pointer version for the Read method of the MagickImage?

Magick.NET/src/Magick.NET/MagickImage.cs

Line 7855 in e20f72b

private unsafe sealed partial class NativeMagickImage : NativeInstance

Describe alternatives you've considered

No response

Additional context

No response

[TonyDragonlake]

duplicated with #1908

[dlemstra]

Why did you create a duplicate issue?

[TonyDragonlake]

Sorry, I have closed the duplicate Issue 1908.
And it is seem that I have found a solution. I want to post my solution here so that anyone has the same request can see it.
To use the native pointer as the image source, we just need to inherit the class System.Buffers.MemoryManager<T>.

    public unsafe class NativeMemoryDelegateManager : MemoryManager<byte>
    {
        private readonly IntPtr m_ptr;
        private readonly int m_len;

        public NativeMemoryDelegateManager(IntPtr ptr, int len)
        {
            if (ptr == IntPtr.Zero)
                throw new ArgumentException("Pointer cannot be null.", nameof(ptr));
            if (len < 0)
                throw new ArgumentOutOfRangeException(nameof(len), "Length must be non-negative.");

            m_ptr = ptr;
            m_len = len;
        }

        public override Span<byte> GetSpan()
        {
            return new Span<byte>(m_ptr.ToPointer(), m_len);
        }

        public override MemoryHandle Pin(int elementIndex = 0)
        {
            if (elementIndex < 0 || elementIndex >= m_len)
                throw new ArgumentOutOfRangeException(nameof(elementIndex));
            var ptr = m_ptr + elementIndex;
            return new MemoryHandle(ptr.ToPointer());
        }

        public override void Unpin() { }
        protected override void Dispose(bool disposing) { }
    }

And then, we can use the ReadPixels method in ReadOnlySpan<byte> version;

  using var image = new MagickImage(filePath);
  var w = image.Width;
  var h = image.Height;
  var channelCount = image.ChannelCount;
  var channels = image.Channels.ToArray();

  var pBuffer = image.GetPixelsUnsafe().GetAreaPointer(0, 0, w, h);
  var length = w * h * channelCount;
  var nmm = new NativeMemoryDelegateManager(pBuffer, (int)length);
  using var image2 = new MagickImage();
  var readSettings = new PixelReadSettings(w, h, StorageType.Quantum, PixelMapping.BGR);
  // use read pixels
  image2.ReadPixels(nmm.GetSpan(), readSettings);

But if the native pointer version could be used, it would be more convenient.

[dlemstra]

I am not sure what you are trying to accomplish but thanks for sharing. The GetAreaPointer gives you access to the native pointer. And it looks like you are creating a clone of the other image, and there is already a method for that.

[TonyDragonlake]

Ah, actually, in my project, all 'images in memory' should implement the following interface:

	public interface IImageBufferHandle : IDisposable
	{
		IntPtr DangerousGetHandle();
		bool AllowDangerousSetHandle { get; }
		bool DangerousSetHandle(IntPtr handle);
		bool ResizeBuffer(uint pixelWidth, uint pixelHeight, uint bitPerPixel);
		uint BufferSize { get; }
		uint BufferStride { get; }
		uint PixelWidth { get; }
		uint PixelHeight { get; }
		uint BitPerPixel { get; }
	}

One of the 'images in memory' is a wrapper for the camera's native memory buffer.

	public sealed class CameraImageBufferHandle : SafeHandleZeroOrMinusOneIsInvalid, IImageBufferHandle 
	{
		// implementation
	}

Then, I need to save the image, but I only have the native pointer.
I don't want any unnecessary memory-copy.
That's why I need a method like ReadPixels(IntPtr data, IPixelReadSettings<QuantumType> settings).

=======================================================================

If it's convenient, I would also like to ask another question:
What is the lifecycle of the native pointer returned by GetAreaPointer method? How can I dispose it manually?

[dlemstra]

You should not dispose that native pointer. The GetAreaPointer method returns you a pointer to the internal memory of a MagickImage. The only way to dispose that pointer would be disposing the IPixelCollection and the image.

[TonyDragonlake]

Thanks for your answer.
By the way, I found that ReadOnlySpan version of the ReadPixels method is not supported for the net6 or 7 apps. Is there any other way to use the ReadPixels method without unnecessary memory copying from native to managed byte array?

[dlemstra]

Both .NET 6 and 7 are out of support and you should really upgrade to net8.0. And I don't understand what you are asking? Your NativeMemoryDelegateManager already does what you want but uses a Span instead of a ReadOnlySpan?