NullReferenceException in Avalonia.Skia when creating a new Bitmap

[SKeehnen]

Describe the bug

With Avalonia 11.1.0-beta2 and 11.1.0-rc1 I get the following error when creating a new Bitmap:

Exception thrown: 'System.NullReferenceException' in Avalonia.Skia.dll: 'Object reference not set to an instance of an object.'
Stack trace:
 >   at Avalonia.Skia.ImmutableBitmap..ctor(PixelSize size, Vector dpi, Int32 stride, PixelFormat format, AlphaFormat alphaFormat, IntPtr data)

This worked without problems in 11.1.0-beta1 and earlier.

To Reproduce

I'm using the following callback function to create an image from a buffer:

public void AfterFrameDraw(nint buffer_data, int frame_num, int width, int height, int bufferWidth, int bufferHeight)
{
    try
    {
        if (isDisposing || width == 0 || height == 0 || bufferWidth == 0 || bufferHeight == 0)
            return;

        if (width == bufferWidth && height == bufferHeight && (width != this.Bounds.Width || height != this.Bounds.Height) && this.Bounds.Width > 0 && this.Bounds.Height > 0)
        {
            width = (int) this.Bounds.Width;
            height = (int) this.Bounds.Height;
        }

        // Mapviewer buffer is a 32-bit RGBA image
        int bufferChannels = 4; // RGBA

        // Get byte array from unmanaged data pointer
        byte[] byteArray = new byte[bufferHeight * bufferWidth * bufferChannels];
        Marshal.Copy(buffer_data, byteArray, 0, bufferHeight * bufferWidth * bufferChannels);

        int bytesPerPixel = 4; // For a 32-bit RGBA image
        byte[] data = new byte[height * width * bytesPerPixel];

        // Calculate the effective width and height to be copied
        int cropWidth = Math.Min(width, bufferWidth);
        int cropHeight = Math.Min(height, bufferHeight);

        Parallel.For(0, cropHeight, k =>
        {
            int srcOffset = ((cropHeight - k - 1) * bufferWidth) * bytesPerPixel;
            int destOffset = k * cropWidth * bytesPerPixel;
            Buffer.BlockCopy(
                byteArray, srcOffset,
                data, destOffset,
                cropWidth * bytesPerPixel);
        });

        Avalonia.Media.Imaging.Bitmap? bmImage = null;

        unsafe
        {
            fixed (byte* p = data)
            {
                IntPtr ptr = (IntPtr) p;

                bmImage = new Avalonia.Media.Imaging.Bitmap(Avalonia.Platform.PixelFormat.Rgba8888, Avalonia.Platform.AlphaFormat.Premul,
                ptr,
                new Avalonia.PixelSize(cropWidth, cropHeight),
                new Avalonia.Vector(96, 96),
                bufferChannels);
            }
        }

        MainThreadHelper.BeginInvokeOnMainThread(() =>
        {
            this.Source = bmImage;
        });

    }
    catch (Exception ex)
    {
        // Handle the exception (logging, etc.)
    }
}

The exception happens at

bmImage = new Avalonia.Media.Imaging.Bitmap(Avalonia.Platform.PixelFormat.Rgba8888, Avalonia.Platform.AlphaFormat.Premul,
                ptr,
                new Avalonia.PixelSize(cropWidth, cropHeight),
                new Avalonia.Vector(96, 96),
                bufferChannels);

Expected behavior

This should just work like it did in 11.1.0-beta1 and earlier.

Avalonia version

11.1.0-beta2, 11.1.0-rc1

OS

Linux

Additional context

No response

[MrJul]

The stride parameter you're providing here (the last one in Bitmap's constructor) is incorrect.
It should probably be cropWidth * bufferChannels.

Before #15520, this parameter was incorrectly ignored so it worked for the wrong reason :)

That being said, we shouldn't throw a NullReferenceException here. Instead, Avalonia should check whether the internal InstallPixels call failed, and throw an ArgumentException for invalid data instead.

[SKeehnen]

Yes that works, thanks @MrJul! Indeed the NullReferenceException had me fooled there. ArgumentException would be the right one.