Fix AV1 still decode lifecycle

HEIF_IMPLEMENTATION_PLAN.md

@@ -95,10 +95,9 @@ This assessment is based on the current source after the upstream ImageSharp mer
 
 ### AV1 decoder
 
-- `Av1Decoder.ReadTile()` checks `tileReader` in the branch where it is known to be null, so the first tile cannot reach reconstruction.
-- Decoder state is allocated or replaced at multiple points, making parsed tile state, reconstructed frame state, and ownership unclear.
+- The single-still `Av1Decoder` path now parses tile state before allocating and reconstructing one frame, and it disposes the reconstruction planes after pixel conversion. Reference-frame, `show_existing_frame`, and multi-frame ownership remain incomplete.
 - The reconstruction pipeline disables loop filtering, CDEF, super-resolution, loop restoration, and padding with constant flags. These are normative stages when signaled, not optional quality improvements.
-- Loop restoration, filter intra prediction, palette paths, `show_existing_frame`, reference/CDF state, and other syntax paths contain `NotImplementedException` or equivalent unsupported branches.
+- Loop restoration, palette paths, `show_existing_frame`, reference/CDF state, and other syntax paths contain `NotImplementedException` or equivalent unsupported branches.
 - The frame buffer now establishes two-byte native sample storage, logical plane rows, and sample-unit block strides for 10/12-bit frames. The active prediction and block reconstruction path is still limited to 8-bit samples and must be connected to the existing high-bit-depth inverse-transform core.
 - `Av1YuvConverter` now consumes the signaled range, supported H.273 matrix coefficients, subsampling, and chroma sample position for 8, 10, and 12-bit output and uses one allocator-backed RGB row. Constant-luminance and chromaticity-derived matrices, ICtCp, and encoder-side subsampling remain incomplete.
 - The inverse-transform path allocates arrays in a per-transform hot path.
@@ -122,7 +121,7 @@ This assessment is based on the current source after the upstream ImageSharp mer
 
 - The repository contains HEIC, HIF, and AVIF assets, but only the legacy JPEG HIF path reaches a full reference-image comparison.
 - HEVC fixtures are identified but not decoded, and there are no HEVC algorithm tests.
-- The strongest AV1 integration test only verifies that the first tile produces non-zero luma data.
+- The strongest AV1 integration test now drives the single-still decoder through tile parsing, reconstruction, and pixel conversion, but only verifies non-zero output rather than independent reference pixels.
 - Several full-image, inverse-transform, entropy, and frame-header cases are disabled or commented out.
 - Existing bitstream, predictor, transform, and entropy unit tests are useful foundations, but many compare two in-tree implementations with the same assumptions.
 - There is no decode matrix covering bit depth, subsampling, range, matrix coefficients, alpha, grids, transformations, metadata, truncated data, or resource limits.

src/ImageSharp/Formats/Heif/Av1/Av1Decoder.cs

@@ -14,7 +14,6 @@ internal class Av1Decoder : IAv1TileReader
     private readonly ObuReader obuReader;
     private readonly Configuration configuration;
     private Av1TileReader? tileReader;
-    private Av1FrameDecoder? frameDecoder;
 
     public Av1Decoder(Configuration configuration)
     {
@@ -28,8 +27,6 @@ internal class Av1Decoder : IAv1TileReader
 
     public Av1FrameInfo? FrameInfo { get; private set; }
 
-    public Av1FrameBuffer<byte>? FrameBuffer { get; private set; }
-
     public Image<TPixel> Decode<TPixel>(Span<byte> buffer)
         where TPixel : unmanaged, IPixel<TPixel>
     {
@@ -40,14 +37,33 @@ internal class Av1Decoder : IAv1TileReader
         Guard.NotNull(this.FrameHeader, nameof(this.FrameHeader));
 
         this.FrameInfo = this.tileReader.FrameInfo;
-        this.FrameBuffer = new(this.configuration, this.SequenceHeader, this.SequenceHeader.ColorConfig.GetColorFormat(), false);
-        this.frameDecoder = new(this.SequenceHeader, this.FrameHeader, this.FrameInfo, this.FrameBuffer);
-        this.frameDecoder.DecodeFrame();
+        using Av1FrameBuffer<byte> frameBuffer = new(
+            this.configuration,
+            this.SequenceHeader,
+            this.SequenceHeader.ColorConfig.GetColorFormat(),
+            false);
+
+        Av1FrameDecoder frameDecoder = new(this.SequenceHeader, this.FrameHeader, this.FrameInfo, frameBuffer);
+        frameDecoder.DecodeFrame();
+
+        Image<TPixel>? resultImage = null;
+        try
+        {
+            resultImage = new Image<TPixel>(
+                this.configuration,
+                this.FrameHeader.FrameSize.FrameWidth,
+                this.FrameHeader.FrameSize.FrameHeight,
+                null);
 
-        Image<TPixel> resultImage = new(this.FrameHeader.FrameSize.FrameWidth, this.FrameHeader.FrameSize.FrameHeight);
-        ImageFrame<TPixel> resultFrame = resultImage.Frames.RootFrame;
-        Av1YuvConverter.ConvertToRgb(this.configuration, this.FrameBuffer, resultFrame);
-        return resultImage;
+            ImageFrame<TPixel> resultFrame = resultImage.Frames.RootFrame;
+            Av1YuvConverter.ConvertToRgb(this.configuration, frameBuffer, resultFrame);
+            return resultImage;
+        }
+        catch
+        {
+            resultImage?.Dispose();
+            throw;
+        }
     }
 
     public void ReadTile(Span<byte> tileData, int tileNum)
@@ -56,13 +72,9 @@ internal class Av1Decoder : IAv1TileReader
         {
             this.SequenceHeader = this.obuReader.SequenceHeader;
             this.FrameHeader = this.obuReader.FrameHeader;
-            Guard.NotNull(this.tileReader, nameof(this.tileReader));
             Guard.NotNull(this.SequenceHeader, nameof(this.SequenceHeader));
             Guard.NotNull(this.FrameHeader, nameof(this.FrameHeader));
-            this.FrameInfo = new(this.SequenceHeader);
-            this.FrameBuffer = new(this.configuration, this.SequenceHeader, this.SequenceHeader.ColorConfig.GetColorFormat(), false);
-            this.frameDecoder = new(this.SequenceHeader, this.FrameHeader, this.FrameInfo, this.FrameBuffer);
-            this.tileReader = new Av1TileReader(this.configuration, this.SequenceHeader, this.FrameHeader, this.frameDecoder);
+            this.tileReader = new Av1TileReader(this.configuration, this.SequenceHeader, this.FrameHeader);
         }
 
         this.tileReader.ReadTile(tileData, tileNum);

src/ImageSharp/Formats/Heif/Av1/Tiling/Av1TileReader.cs

@@ -33,14 +33,13 @@ internal class Av1TileReader : IAv1TileReader
     private readonly int[] firstTransformOffset = new int[2];
     private readonly int[] coefficientIndex = [];
     private readonly Configuration configuration;
-    private readonly IAv1FrameDecoder frameDecoder;
+    private readonly IAv1FrameDecoder? frameDecoder;
 
-    public Av1TileReader(Configuration configuration, ObuSequenceHeader sequenceHeader, ObuFrameHeader frameHeader, IAv1FrameDecoder frameDecoder)
+    public Av1TileReader(Configuration configuration, ObuSequenceHeader sequenceHeader, ObuFrameHeader frameHeader)
     {
         this.FrameHeader = frameHeader;
         this.configuration = configuration;
         this.SequenceHeader = sequenceHeader;
-        this.frameDecoder = frameDecoder;
 
         // init_main_frame_ctxt
         this.FrameInfo = new(this.SequenceHeader);
@@ -66,6 +65,10 @@ internal class Av1TileReader : IAv1TileReader
         this.coefficientIndex = new int[Av1Constants.MaxPlanes];
     }
 
+    public Av1TileReader(Configuration configuration, ObuSequenceHeader sequenceHeader, ObuFrameHeader frameHeader, IAv1FrameDecoder frameDecoder)
+        : this(configuration, sequenceHeader, frameHeader)
+        => this.frameDecoder = frameDecoder;
+
     public ObuFrameHeader FrameHeader { get; }
 
     public ObuSequenceHeader SequenceHeader { get; }
@@ -126,7 +129,7 @@ internal class Av1TileReader : IAv1TileReader
                 this.ParsePartition(ref reader, modeInfoPosition, superBlockSize, superblockInfo, tileInfo);
 
                 // decoding of the superblock
-                this.frameDecoder.DecodeSuperblock(modeInfoPosition, superblockInfo, tileInfo);
+                this.frameDecoder?.DecodeSuperblock(modeInfoPosition, superblockInfo, tileInfo);
             }
         }
     }

tests/ImageSharp.Tests/Formats/Heif/Av1/Av1TilingTests.cs

@@ -6,12 +6,27 @@ using SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 using SixLabors.ImageSharp.Formats.Heif.Av1.Pipeline;
 using SixLabors.ImageSharp.Formats.Heif.Av1.Tiling;
 using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Tests.Formats.Heif.Av1;
 
 [Trait("Format", "Avif")]
 public class Av1TilingTests
 {
+    [Fact]
+    public void DecoderReadsFirstTile()
+    {
+        string filePath = Path.Combine(TestEnvironment.InputImagesDirectoryFullPath, TestImages.Heif.Orange4x4);
+        byte[] content = File.ReadAllBytes(filePath);
+        Av1Decoder decoder = new(Configuration.Default);
+
+        using Image<Rgba32> image = decoder.Decode<Rgba32>(content.AsSpan(0x010E, 0x001D));
+
+        Assert.Equal(4, image.Width);
+        Assert.Equal(4, image.Height);
+        Assert.True(image.Frames.RootFrame.PixelBuffer.DangerousGetSingleSpan().ContainsAnyExcept(default(Rgba32)));
+    }
+
     [Theory]
     [InlineData(TestImages.Heif.Orange4x4, 0x010E, 0x001d, 21, 1)]
     public void DecodePixelsFirstTile(string filename, int dataOffset, int dataSize, int tileOffset, int superblockCount)