update write block in huffman encoder, add test

src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanScanEncoder.cs

@@ -263,7 +263,6 @@ public void EncodeDcScan(Component component, CancellationToken cancellationToke
                     ref Unsafe.Add(ref blockRef, k),
                     ref dcHuffmanTable);
 
-
                 if (this.IsStreamFlushNeeded)
                 {
                     this.FlushToStream();
@@ -492,6 +491,7 @@ private void WriteAcBlock(
             }
         }
 
+        // if mcu block contains trailing zeros - we must write end of block (EOB) value indicating that current block is over
         if (runLength > 0)
         {
             this.EmitHuff(acHuffTable, 0x00);
@@ -505,44 +505,7 @@ private void WriteBlock(
         ref HuffmanLut acTable)
     {
         this.WriteDc(component, ref block, ref dcTable);
-
-        // Emit the AC components.
-        int[] acHuffTable = acTable.Values;
-
-        nint lastValuableIndex = block.GetLastNonZeroIndex();
-
-        int runLength = 0;
-        ref short blockRef = ref Unsafe.As<Block8x8, short>(ref block);
-        for (nint zig = 1; zig <= lastValuableIndex; zig++)
-        {
-            const int zeroRun1 = 1 << 4;
-            const int zeroRun16 = 16 << 4;
-
-            int ac = Unsafe.Add(ref blockRef, zig);
-            if (ac == 0)
-            {
-                runLength += zeroRun1;
-            }
-            else
-            {
-                while (runLength >= zeroRun16)
-                {
-                    this.EmitHuff(acHuffTable, 0xf0);
-                    runLength -= zeroRun16;
-                }
-
-                this.EmitHuffRLE(acHuffTable, runLength, ac);
-                runLength = 0;
-            }
-        }
-
-        // if mcu block contains trailing zeros - we must write end of block (EOB) value indicating that current block is over
-        // this can be done for any number of trailing zeros, even when all 63 ac values are zero
-        // (Block8x8F.Size - 1) == 63 - last index of the mcu elements
-        if (lastValuableIndex != Block8x8F.Size - 1)
-        {
-            this.EmitHuff(acHuffTable, 0x00);
-        }
+        this.WriteAcBlock(ref block, 1, 64, ref acTable);
     }
 
     /// <summary>

tests/ImageSharp.Tests/Formats/Jpg/JpegEncoderTests.cs

@@ -14,13 +14,6 @@ public partial class JpegEncoderTests
 {
     private static JpegEncoder JpegEncoder => new();
 
-    private static readonly TheoryData<int> TestQualities = new()
-    {
-        40,
-        80,
-        100,
-    };
-
     public static readonly TheoryData<JpegEncodingColor, int, float> NonSubsampledEncodingSetups = new()
     {
         { JpegEncodingColor.Rgb, 100, 0.0238f / 100 },
@@ -160,6 +153,31 @@ public void EncodeBaseline_WorksWithDiscontiguousBuffers<TPixel>(TestImageProvid
         TestJpegEncoderCore(provider, colorType, 100, comparer);
     }
 
+    [Theory]
+    [WithFile(TestImages.Png.CalliphoraPartial, nameof(NonSubsampledEncodingSetups), PixelTypes.Rgb24)]
+    [WithFile(TestImages.Png.CalliphoraPartial, nameof(SubsampledEncodingSetups), PixelTypes.Rgb24)]
+    [WithFile(TestImages.Png.BikeGrayscale, nameof(LuminanceEncodingSetups), PixelTypes.L8)]
+    [WithFile(TestImages.Jpeg.Baseline.Cmyk, nameof(CmykEncodingSetups), PixelTypes.Rgb24)]
+    [WithFile(TestImages.Jpeg.Baseline.Ycck, nameof(YcckEncodingSetups), PixelTypes.Rgb24)]
+    public void EncodeProgressive_DefaultNumberOfScans<TPixel>(TestImageProvider<TPixel> provider, JpegEncodingColor colorType, int quality, float tolerance)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage();
+
+        JpegEncoder encoder = new()
+        {
+            Quality = quality,
+            ColorType = colorType,
+            Progressive = true
+        };
+        string info = $"{colorType}-Q{quality}";
+
+        ImageComparer comparer = new TolerantImageComparer(tolerance);
+
+        // Does DebugSave & load reference CompareToReferenceInput():
+        image.VerifyEncoder(provider, "jpeg", info, encoder, comparer, referenceImageExtension: "jpg");
+    }
+
     [Theory]
     [InlineData(JpegEncodingColor.YCbCrRatio420)]
     [InlineData(JpegEncodingColor.YCbCrRatio444)]