Converting code from System.Drawing to Imagesharp

[Symbai]

I'm using the following constructor in System.Drawing to load an image from IntPtr (Scan0). How can I achieve this using Imagesharp?

Bitmap newBitmap = new Bitmap(width, height, stride, PixelFormat.Format32bppArgb, (IntPtr)scan0);

[antonfirsov]

Image.LoadPixelData with a ReadOnlySpan of pixels (made from scan0):

ImageSharp/src/ImageSharp/Image.LoadPixelData.cs

Line 38 in 2b85b55

public static Image<TPixel> LoadPixelData<TPixel>(ReadOnlySpan<TPixel> data, int width, int height)

Format32bppArgb matches our Rgba32 AFAIK. Edit: Sorry it's gonna be Bgra32

[Symbai]

How do I make a readonlyspan of pixels from scan0 since its a pointer and I don't know how much I should read from it.

[antonfirsov]

You need this constructor to read width * height of Bgra32-s. If you are new to Span<T> and ReadOnlySpan<T>, I recommend to have a quick look at the following intros:
https://www.codemag.com/Article/1807051/Introducing-.NET-Core-2.1-Flagship-Types-Span-T-and-Memory-T
https://docs.microsoft.com/en-us/archive/msdn-magazine/2018/january/csharp-all-about-span-exploring-a-new-net-mainstay

Your code should be something like this, assuming scan0 is a pointer:

var span = new ReadOnlySpan<Bgra32>(scan0, width * height);
using var image = Image.LoadPixelData<Bgra32>(span, width, height);

Note that LoadPixelData does not support stride with extra padding, all pixel rows in the memory area pointed by scan0 should be exactly of length width * height * sizeof(Bgra32) for the above code to work.