What causes "Need skia to dump textures, sorry" in AvaloniaUI/Avalonia?

Initialize and keep a valid Skia GrContext bound to the Vulkan device so SaveTexture can use it.

AvaloniaUI/Avalonia · error · NotSupportedException

Need skia to dump textures, sorry

Error message

Need skia to dump textures, sorry

What it means

In SaveTexture, when there is no Skia GPU context (_vk.GrContext == null) and no IOSurface path available, the sample throws NotSupportedException. It means the texture-dump fallback requires Skia (GrContext) to read GPU pixels, and on non-macOS without Skia it cannot proceed.

Source

Thrown at samples/GpuInterop/VulkanDemo/VulkanImage.cs:365

                {
                    var surf = ExportIOSurface();
                    if (NativeMethods.IOSurfaceLock(surf, 0, IntPtr.Zero) != 0)
                        throw new Exception("IOSurfaceLock failed");
                    var w = (int)NativeMethods.IOSurfaceGetWidth(surf);
                    var h = (int)NativeMethods.IOSurfaceGetHeight(surf);
                    var sstride = NativeMethods.IOSurfaceGetBytesPerRow(surf);

                    var pSurface = NativeMethods.IOSurfaceGetBaseAddress(surf);
                    using var b = new Avalonia.Media.Imaging.Bitmap(PixelFormat.Bgra8888,
                        AlphaFormat.Premul, pSurface, new PixelSize(w, h),
                        new Vector(96, 96), (int)sstride);
                    b.Save(path, PngBitmapEncoderOptions.Default);

                    NativeMethods.IOSurfaceUnlock(surf, 0, IntPtr.Zero);
                    return;
                }
                else
                    throw new NotSupportedException("Need skia to dump textures, sorry");
            }

            _vk.GrContext.ResetContext();
            var _image = this;
            var imageInfo = new GRVkImageInfo()
            {
                CurrentQueueFamily = _vk.QueueFamilyIndex,
                Format = (uint)_image.Format,
                Image = _image.Handle,
                ImageLayout = (uint)_image.CurrentLayout,
                ImageTiling = (uint)_image.Tiling,
                ImageUsageFlags = (uint)_image.UsageFlags,
                LevelCount = _image.MipLevels,
                SampleCount = 1,
                Protected = false,
                Alloc = new GRVkAlloc()
                {
                    Memory = _image.MemoryHandle, Flags = 0, Offset = 0, Size = _image.MemorySize

View on GitHub (pinned to 11c5427268)

Solutions

Initialize and keep a valid Skia GrContext bound to the Vulkan device so SaveTexture can use it.
On macOS, ensure _hasIOSurface is true so the IOSurface dump path is taken instead.
Avoid calling SaveTexture when no GPU readback backend (Skia or IOSurface) is available.
Implement a plain vkCmdCopyImageToBuffer readback fallback if Skia is undesirable.

Example fix

// before
else
    throw new NotSupportedException("Need skia to dump textures, sorry");

// after (explicit, actionable)
else
    throw new NotSupportedException(
        "Texture dump requires a Skia GrContext (or an IOSurface on macOS). Initialize _vk.GrContext before calling SaveTexture.");

Defensive patterns

Strategy: validation

Validate before calling

// only attempt a dump if a readback backend exists
var canDump = _vk.GrContext is not null || (OperatingSystem.IsOSPlatform(OSPlatform.OSX) && _hasIOSurface);
if (!canDump) return;

Type guard

static bool HasReadbackBackend(VulkanImage img) => img._vk.GrContext is not null || img._hasIOSurface;

Try / catch

try { SaveTexture(path); }
catch (NotSupportedException ex) when (ex.Message.Contains("skia"))
{ _logger.LogWarning("No Skia GPU context; cannot dump texture."); }

Prevention

Initialize a Skia GrContext on Linux/Windows if you need texture dumps.
On macOS, ensure _hasIOSurface so the IOSurface path is used.
Gate SaveTexture behind a readback-backend check.

When it happens

Trigger: Calling SaveTexture when the demo has no GrContext (SkiaSharp GPU context) wired up and the platform is not macOS-with-IOSurface. The code only handles IOSurface on macOS; everything else routes through Skia, which is absent here.

Common situations: Running the Vulkan demo on Linux/Windows where the Skia GPU bridge was not initialized; GrContext disposed before dump; trimming/AOT removing Skia.

Related errors

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/70c165d439782061. Report an issue: GitHub.