Correct readonly-semantics for QuantizedFrame

src/ImageSharp/Advanced/AotCompilerTools.cs

@@ -104,7 +104,7 @@ namespace SixLabors.ImageSharp.Advanced
         private static void AotCompileWuQuantizer<TPixel>()
             where TPixel : struct, IPixel<TPixel>
         {
-            var test = new WuFrameQuantizer<TPixel>(new WuQuantizer(false));
+            var test = new WuFrameQuantizer<TPixel>(Configuration.Default.MemoryAllocator, new WuQuantizer(false));
             test.QuantizeFrame(new ImageFrame<TPixel>(Configuration.Default, 1, 1));
             test.AotGetPalette();
         }

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -164,7 +164,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
                         using (QuantizedFrame<TPixel> paletteQuantized = palleteFrameQuantizer.QuantizeFrame(frame))
                         {
                             this.WriteImageData(paletteQuantized, stream);
-                        }    
+                        }
                     }
                 }
             }

src/ImageSharp/Formats/Gif/LzwEncoder.cs

@@ -180,7 +180,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
         /// </summary>
         /// <param name="indexedPixels">The span of indexed pixels.</param>
         /// <param name="stream">The stream to write to.</param>
-        public void Encode(Span<byte> indexedPixels, Stream stream)
+        public void Encode(ReadOnlySpan<byte> indexedPixels, Stream stream)
         {
             // Write "initial code size" byte
             stream.WriteByte((byte)this.initialCodeSize);
@@ -251,7 +251,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
         /// <param name="indexedPixels">The span of indexed pixels.</param>
         /// <param name="intialBits">The initial bits.</param>
         /// <param name="stream">The stream to write to.</param>
-        private void Compress(Span<byte> indexedPixels, int intialBits, Stream stream)
+        private void Compress(ReadOnlySpan<byte> indexedPixels, int intialBits, Stream stream)
         {
             int fcode;
             int c;
@@ -375,7 +375,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
         /// The <see cref="int"/>
         /// </returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private int NextPixel(Span<byte> indexedPixels)
+        private int NextPixel(ReadOnlySpan<byte> indexedPixels)
         {
             return indexedPixels[this.position++] & 0xFF;
         }

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -676,7 +676,7 @@ namespace SixLabors.ImageSharp.Formats.Png
             {
                 ref byte colorTableRef = ref MemoryMarshal.GetReference(colorTable.GetSpan());
                 ref byte alphaTableRef = ref MemoryMarshal.GetReference(alphaTable.GetSpan());
-                Span<byte> quantizedSpan = quantized.GetPixelSpan();
+                ReadOnlySpan<byte> quantizedSpan = quantized.GetPixelSpan();
 
                 Rgba32 rgba = default;
 

src/ImageSharp/Processing/Processors/Quantization/FrameQuantizer{TPixel}.cs

@@ -85,7 +85,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         }
 
         /// <inheritdoc/>
-        public virtual QuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image)
+        public QuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image)
         {
             Guard.NotNull(image, nameof(image));
 
@@ -112,17 +112,18 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
 
             var quantizedFrame = new QuantizedFrame<TPixel>(image.MemoryAllocator, width, height, palette);
 
+            Span<byte> pixelSpan = quantizedFrame.GetWritablePixelSpan();
             if (this.Dither)
             {
                 // We clone the image as we don't want to alter the original via dithering.
                 using (ImageFrame<TPixel> clone = image.Clone())
                 {
-                    this.SecondPass(clone, quantizedFrame.GetPixelSpan(), palette.Span, width, height);
+                    this.SecondPass(clone, pixelSpan, palette.Span, width, height);
                 }
             }
             else
             {
-                this.SecondPass(image, quantizedFrame.GetPixelSpan(), palette.Span, width, height);
+                this.SecondPass(image, pixelSpan, palette.Span, width, height);
             }
 
             return quantizedFrame;

src/ImageSharp/Processing/Processors/Quantization/QuantizeProcessor{TPixel}.cs

@@ -45,7 +45,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                     ReadOnlySpan<byte> quantizedPixelSpan = quantized.GetPixelSpan();
 
                     ReadOnlySpan<TPixel> paletteSpan = quantized.Palette.Span;
-                    
+
                     int yy = y * source.Width;
 
                     for (int x = 0; x < source.Width; x++)

src/ImageSharp/Processing/Processors/Quantization/QuantizedFrame{TPixel}.cs

@@ -27,7 +27,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// <param name="width">The image width.</param>
         /// <param name="height">The image height.</param>
         /// <param name="palette">The color palette.</param>
-        public QuantizedFrame(MemoryAllocator memoryAllocator, int width, int height, ReadOnlyMemory<TPixel> palette)
+        internal QuantizedFrame(MemoryAllocator memoryAllocator, int width, int height, ReadOnlyMemory<TPixel> palette)
         {
             Guard.MustBeGreaterThan(width, 0, nameof(width));
             Guard.MustBeGreaterThan(height, 0, nameof(height));
@@ -58,7 +58,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// </summary>
         /// <returns>The <see cref="Span{T}"/></returns>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public Span<byte> GetPixelSpan() => this.pixels.GetSpan();
+        public ReadOnlySpan<byte> GetPixelSpan() => this.pixels.GetSpan();
 
         /// <summary>
         /// Gets the representation of the pixels as a <see cref="Span{T}"/> of contiguous memory
@@ -67,7 +67,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// <param name="rowIndex">The row.</param>
         /// <returns>The <see cref="Span{T}"/></returns>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public Span<byte> GetRowSpan(int rowIndex) => this.GetPixelSpan().Slice(rowIndex * this.Width, this.Width);
+        public ReadOnlySpan<byte> GetRowSpan(int rowIndex) => this.GetPixelSpan().Slice(rowIndex * this.Width, this.Width);
 
         /// <inheritdoc/>
         public void Dispose()
@@ -76,5 +76,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             this.pixels = null;
             this.Palette = null;
         }
+
+        /// <summary>
+        /// Get the non-readonly span of pixel data so <see cref="FrameQuantizer{TPixel}"/> can fill it.
+        /// </summary>
+        internal Span<byte> GetWritablePixelSpan() => this.pixels.GetSpan();
     }
 }

src/ImageSharp/Processing/Processors/Quantization/WuFrameQuantizer{TPixel}.cs

@@ -120,33 +120,31 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// <summary>
         /// Initializes a new instance of the <see cref="WuFrameQuantizer{TPixel}"/> class.
         /// </summary>
+        /// <param name="memoryAllocator">The <see cref="MemoryAllocator"/>.</param>
         /// <param name="quantizer">The wu quantizer</param>
         /// <remarks>
         /// The Wu quantizer is a two pass algorithm. The initial pass sets up the 3-D color histogram,
         /// the second pass quantizes a color based on the position in the histogram.
         /// </remarks>
-        public WuFrameQuantizer(WuQuantizer quantizer)
-            : this(quantizer, quantizer.MaxColors)
+        public WuFrameQuantizer(MemoryAllocator memoryAllocator, WuQuantizer quantizer)
+            : this(memoryAllocator, quantizer, quantizer.MaxColors)
         {
         }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="WuFrameQuantizer{TPixel}"/> class.
         /// </summary>
+        /// <param name="memoryAllocator">The <see cref="MemoryAllocator"/>.</param>
         /// <param name="quantizer">The wu quantizer.</param>
         /// <param name="maxColors">The maximum number of colors to hold in the color palette.</param>
         /// <remarks>
         /// The Wu quantizer is a two pass algorithm. The initial pass sets up the 3-D color histogram,
         /// the second pass quantizes a color based on the position in the histogram.
         /// </remarks>
-        public WuFrameQuantizer(WuQuantizer quantizer, int maxColors)
-            : base(quantizer, false) => this.colors = maxColors;
-
-        /// <inheritdoc/>
-        public override QuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image)
+        public WuFrameQuantizer(MemoryAllocator memoryAllocator, WuQuantizer quantizer, int maxColors)
+            : base(quantizer, false)
         {
-            Guard.NotNull(image, nameof(image));
-            MemoryAllocator memoryAllocator = image.MemoryAllocator;
+            Guard.NotNull(memoryAllocator, nameof(memoryAllocator));
 
             this.vwt = memoryAllocator.Allocate<long>(TableLength, AllocationOptions.Clean);
             this.vmr = memoryAllocator.Allocate<long>(TableLength, AllocationOptions.Clean);
@@ -156,7 +154,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             this.m2 = memoryAllocator.Allocate<double>(TableLength, AllocationOptions.Clean);
             this.tag = memoryAllocator.Allocate<byte>(TableLength, AllocationOptions.Clean);
 
-            return base.QuantizeFrame(image);
+            this.colors = maxColors;
         }
 
         /// <inheritdoc/>
@@ -169,6 +167,14 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             this.vma?.Dispose();
             this.m2?.Dispose();
             this.tag?.Dispose();
+
+            this.vwt = null;
+            this.vmr = null;
+            this.vmg = null;
+            this.vmb = null;
+            this.vma = null;
+            this.m2 = null;
+            this.tag = null;
         }
 
         internal ReadOnlyMemory<TPixel> AotGetPalette() => this.GetPalette();

src/ImageSharp/Processing/Processors/Quantization/WuQuantizer.cs

@@ -72,14 +72,18 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// <inheritdoc />
         public IFrameQuantizer<TPixel> CreateFrameQuantizer<TPixel>(Configuration configuration)
             where TPixel : struct, IPixel<TPixel>
-            => new WuFrameQuantizer<TPixel>(this);
+        {
+            Guard.NotNull(configuration, nameof(configuration));
+            return new WuFrameQuantizer<TPixel>(configuration.MemoryAllocator, this);
+        }
 
         /// <inheritdoc/>
         public IFrameQuantizer<TPixel> CreateFrameQuantizer<TPixel>(Configuration configuration, int maxColors)
             where TPixel : struct, IPixel<TPixel>
         {
+            Guard.NotNull(configuration, nameof(configuration));
             maxColors = maxColors.Clamp(QuantizerConstants.MinColors, QuantizerConstants.MaxColors);
-            return new WuFrameQuantizer<TPixel>(this, maxColors);
+            return new WuFrameQuantizer<TPixel>(configuration.MemoryAllocator, this, maxColors);
         }
 
         private static IErrorDiffuser GetDiffuser(bool dither) => dither ? KnownDiffusers.FloydSteinberg : null;