AvaloniaUI/Avalonia · error · ArgumentException

Size should be >= (1,1)

Error message

Size should be >= (1,1)

What it means

WriteableBitmap.CreatePlatformImpl throws ArgumentException(nameof(size)) when size.Width <= 0 || size.Height <= 0. A bitmap must have at least one pixel in each dimension. This guard runs in every constructor path and DecodeToHeight, so a decoded stream that yields zero dimensions also surfaces here.

Source

Thrown at src/Avalonia.Base/Media/Imaging/WriteableBitmap.cs:127

        /// <summary>
        /// Loads a Bitmap from a stream and decodes at the desired height. Aspect ratio is maintained.
        /// This is more efficient than loading and then resizing.
        /// </summary>
        /// <param name="stream">The stream to read the bitmap from. This can be any supported image format.</param>
        /// <param name="height">The desired height of the resulting bitmap.</param>
        /// <param name="interpolationMode">The <see cref="BitmapInterpolationMode"/> to use should any scaling be required.</param>
        /// <returns>An instance of the <see cref="WriteableBitmap"/> class.</returns>
        public new static WriteableBitmap DecodeToHeight(Stream stream, int height, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
        {
            var ri = GetFactory();

            return new WriteableBitmap(ri.LoadWriteableBitmapToHeight(stream, height, interpolationMode));
        }

        private static (IBitmapImpl, BitmapMemory?) CreatePlatformImpl(PixelSize size, in Vector dpi, PixelFormat? format, AlphaFormat? alphaFormat)
        {
            if (size.Width <= 0 || size.Height <= 0)
                throw new ArgumentException("Size should be >= (1,1)", nameof(size));
            
            var ri = GetFactory();

            PixelFormat finalFormat = format ?? ri.DefaultPixelFormat;
            AlphaFormat finalAlphaFormat = alphaFormat ?? ri.DefaultAlphaFormat;

            if (ri.IsSupportedBitmapPixelFormat(finalFormat))
                return (ri.CreateWriteableBitmap(size, dpi, finalFormat, finalAlphaFormat), null);

            if (!PixelFormatReader.SupportsFormat(finalFormat))
                throw new NotSupportedException($"Pixel format {finalFormat} is not supported");

            finalAlphaFormat = finalFormat.HasAlpha ? finalAlphaFormat : Platform.AlphaFormat.Opaque;

            var impl = ri.CreateWriteableBitmap(size, dpi, PixelFormat.Rgba8888, finalAlphaFormat);
            return (impl, new BitmapMemory(finalFormat, finalAlphaFormat, size));
        }

View on GitHub (pinned to 11c5427268)

Solutions

1. Ensure width and height are >= 1 before constructing.
2. Validate the stream decodes to a non-zero size (decode to a Bitmap first to inspect PixelSize).
3. Guard callers that derive size from external input against zero/negative values.

Example fix

// before
var wb = new WriteableBitmap(new PixelSize(0, 0), dpi, PixelFormat.Bgra8888);

// after
if (size.Width < 1 || size.Height < 1)
    throw new ArgumentException("Bitmap size must be at least 1x1.", nameof(size));
var wb = new WriteableBitmap(new PixelSize(Math.Max(1,size.Width), Math.Max(1,size.Height)), dpi, PixelFormat.Bgra8888);

if (size.Width < 1 || size.Height < 1)
    throw new ArgumentException("Size must be >= (1,1).", nameof(size));
var wb = new WriteableBitmap(size, dpi, PixelFormat.Bgra8888);

When it happens

Trigger: Constructing a WriteableBitmap with PixelSize(0,0) or negative dimensions; calling DecodeToHeight on a corrupt/empty stream that decodes to a zero-size image.

Common situations: Passing a UI Size or a default PixelSize; decoding a truncated or unsupported image file; computing dimensions from DPI/scale and rounding to zero.

Related errors

• stride
• {nameof(KeySpline)} must have X coordinates >= 0.0 and <= 1.
• Invalid KeySpline X1 value. Must be >= 0.0 and <= 1.0.
• Invalid KeySpline X2 value. Must be >= 0.0 and <= 1.0.
• Invalid application identifier

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/611bb641f0444c04. Report an issue: GitHub.