Merge pull request #1662 from SixLabors/bp/tiffavoidsinglespan

TiffEncoder: Avoid buffer2D.GetSingleSpan() and use GetPixelRowSpan instead

src/ImageSharp/Formats/Tiff/Compression/Compressors/T4BitCompressor.cs

@@ -213,7 +213,9 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Compressors
             this.compressedDataBuffer = this.Allocator.Allocate<byte>(maxNeededBytes);
         }
 
-        /// <summary>Writes a image compressed with CCITT T4 to the stream.</summary>
+        /// <summary>
+        /// Writes a image compressed with CCITT T4 to the stream.
+        /// </summary>
         /// <param name="pixelsAsGray">The pixels as 8-bit gray array.</param>
         /// <param name="height">The strip height.</param>
         public override void CompressStrip(Span<byte> pixelsAsGray, int height)

src/ImageSharp/Formats/Tiff/Writers/TiffBaseColorWriter{TPixel}.cs

@@ -79,10 +79,6 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Writers
             this.Dispose(true);
         }
 
-        protected static Span<T> GetStripPixels<T>(Buffer2D<T> buffer2D, int y, int height)
-            where T : struct
-            => buffer2D.GetSingleSpan().Slice(y * buffer2D.Width, height * buffer2D.Width);
-
         protected abstract void EncodeStrip(int y, int height, TiffBaseCompressor compressor);
 
         /// <summary>

src/ImageSharp/Formats/Tiff/Writers/TiffBiColorWriter{TPixel}.cs

@@ -36,38 +36,50 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Writers
         /// <inheritdoc/>
         protected override void EncodeStrip(int y, int height, TiffBaseCompressor compressor)
         {
-            this.pixelsAsGray ??= this.MemoryAllocator.Allocate<byte>(height * this.Image.Width);
-
-            Span<byte> pixelAsGraySpan = this.pixelsAsGray.Slice(0, height * this.Image.Width);
-
-            Span<TPixel> pixelsBlackWhite = GetStripPixels(this.imageBlackWhite.GetRootFramePixelBuffer(), y, height);
-
-            PixelOperations<TPixel>.Instance.ToL8Bytes(this.Configuration, pixelsBlackWhite, pixelAsGraySpan, pixelsBlackWhite.Length);
+            int width = this.Image.Width;
 
             if (compressor.Method == TiffCompression.CcittGroup3Fax || compressor.Method == TiffCompression.Ccitt1D)
             {
                 // Special case for T4BitCompressor.
-                compressor.CompressStrip(pixelAsGraySpan, height);
+                int stripPixels = width * height;
+                this.pixelsAsGray ??= this.MemoryAllocator.Allocate<byte>(stripPixels);
+                Span<byte> pixelAsGraySpan = this.pixelsAsGray.GetSpan();
+                int lastRow = y + height;
+                int grayRowIdx = 0;
+                for (int row = y; row < lastRow; row++)
+                {
+                    Span<TPixel> pixelsBlackWhiteRow = this.imageBlackWhite.GetPixelRowSpan(row);
+                    Span<byte> pixelAsGrayRow = pixelAsGraySpan.Slice(grayRowIdx * width, width);
+                    PixelOperations<TPixel>.Instance.ToL8Bytes(this.Configuration, pixelsBlackWhiteRow, pixelAsGrayRow, width);
+                    grayRowIdx++;
+                }
+
+                compressor.CompressStrip(pixelAsGraySpan.Slice(0, stripPixels), height);
             }
             else
             {
                 // Write uncompressed image.
                 int bytesPerStrip = this.BytesPerRow * height;
                 this.bitStrip ??= this.MemoryAllocator.AllocateManagedByteBuffer(bytesPerStrip);
+                this.pixelsAsGray ??= this.MemoryAllocator.Allocate<byte>(width);
+                Span<byte> pixelAsGraySpan = this.pixelsAsGray.GetSpan();
 
                 Span<byte> rows = this.bitStrip.Slice(0, bytesPerStrip);
                 rows.Clear();
 
-                int grayPixelIndex = 0;
-                for (int s = 0; s < height; s++)
+                int outputRowIdx = 0;
+                int lastRow = y + height;
+                for (int row = y; row < lastRow; row++)
                 {
                     int bitIndex = 0;
                     int byteIndex = 0;
-                    Span<byte> outputRow = rows.Slice(s * this.BytesPerRow);
+                    Span<byte> outputRow = rows.Slice(outputRowIdx * this.BytesPerRow);
+                    Span<TPixel> pixelsBlackWhiteRow = this.imageBlackWhite.GetPixelRowSpan(row);
+                    PixelOperations<TPixel>.Instance.ToL8Bytes(this.Configuration, pixelsBlackWhiteRow, pixelAsGraySpan, width);
                     for (int x = 0; x < this.Image.Width; x++)
                     {
                         int shift = 7 - bitIndex;
-                        if (pixelAsGraySpan[grayPixelIndex++] == 255)
+                        if (pixelAsGraySpan[x] == 255)
                         {
                             outputRow[byteIndex] |= (byte)(1 << shift);
                         }
@@ -79,6 +91,8 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Writers
                             bitIndex = 0;
                         }
                     }
+
+                    outputRowIdx++;
                 }
 
                 compressor.CompressStrip(rows, height);

src/ImageSharp/Formats/Tiff/Writers/TiffCompositeColorWriter{TPixel}.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
 using SixLabors.ImageSharp.Formats.Tiff.Compression;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
@@ -30,12 +31,22 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Writers
 
             this.rowBuffer.Clear();
 
-            Span<byte> rowSpan = this.rowBuffer.GetSpan().Slice(0, this.BytesPerRow * height);
+            Span<byte> outputRowSpan = this.rowBuffer.GetSpan().Slice(0, this.BytesPerRow * height);
 
-            Span<TPixel> pixels = GetStripPixels(this.Image.PixelBuffer, y, height);
+            int width = this.Image.Width;
+            using IMemoryOwner<TPixel> stripPixelBuffer = this.MemoryAllocator.Allocate<TPixel>(height * width);
+            Span<TPixel> stripPixels = stripPixelBuffer.GetSpan();
+            int lastRow = y + height;
+            int stripPixelsRowIdx = 0;
+            for (int row = y; row < lastRow; row++)
+            {
+                Span<TPixel> stripPixelsRow = this.Image.PixelBuffer.GetRowSpan(row);
+                stripPixelsRow.CopyTo(stripPixels.Slice(stripPixelsRowIdx * width, width));
+                stripPixelsRowIdx++;
+            }
 
-            this.EncodePixels(pixels, rowSpan);
-            compressor.CompressStrip(rowSpan, height);
+            this.EncodePixels(stripPixels, outputRowSpan);
+            compressor.CompressStrip(outputRowSpan, height);
         }
 
         protected abstract void EncodePixels(Span<TPixel> pixels, Span<byte> buffer);

src/ImageSharp/Formats/Tiff/Writers/TiffPaletteWriter{TPixel}.cs

@@ -5,7 +5,6 @@ using System;
 using System.Buffers;
 using System.Runtime.InteropServices;
 
-using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Formats.Tiff.Compression;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
@@ -21,6 +20,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Writers
         private readonly int colorPaletteSize;
         private readonly int colorPaletteBytes;
         private readonly IndexedImageFrame<TPixel> quantizedImage;
+        private IMemoryOwner<byte> indexedPixelsBuffer;
 
         public TiffPaletteWriter(
             ImageFrame<TPixel> image,
@@ -55,22 +55,24 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Writers
         /// <inheritdoc />
         protected override void EncodeStrip(int y, int height, TiffBaseCompressor compressor)
         {
-            Span<byte> indexedPixels = GetStripPixels(((IPixelSource)this.quantizedImage).PixelBuffer, y, height);
+            int width = this.Image.Width;
+
             if (this.BitsPerPixel == 4)
             {
-                int width = this.Image.Width;
                 int halfWidth = width >> 1;
                 int excess = (width & 1) * height; // (width % 2) * height
                 int rows4BitBufferLength = (halfWidth * height) + excess;
-                using IMemoryOwner<byte> rows4bitBuffer = this.MemoryAllocator.Allocate<byte>(rows4BitBufferLength);
-                Span<byte> rows4bit = rows4bitBuffer.GetSpan();
-                int idxPixels = 0;
+                this.indexedPixelsBuffer ??= this.MemoryAllocator.Allocate<byte>(rows4BitBufferLength);
+                Span<byte> rows4bit = this.indexedPixelsBuffer.GetSpan();
                 int idx4bitRows = 0;
-                for (int row = 0; row < height; row++)
+                int lastRow = y + height;
+                for (int row = y; row < lastRow; row++)
                 {
+                    ReadOnlySpan<byte> indexedPixelRow = this.quantizedImage.GetPixelRowSpan(row);
+                    int idxPixels = 0;
                     for (int x = 0; x < halfWidth; x++)
                     {
-                        rows4bit[idx4bitRows] = (byte)((indexedPixels[idxPixels] << 4) | (indexedPixels[idxPixels + 1] & 0xF));
+                        rows4bit[idx4bitRows] = (byte)((indexedPixelRow[idxPixels] << 4) | (indexedPixelRow[idxPixels + 1] & 0xF));
                         idxPixels += 2;
                         idx4bitRows++;
                     }
@@ -78,7 +80,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Writers
                     // Make sure rows are byte-aligned.
                     if (width % 2 != 0)
                     {
-                        rows4bit[idx4bitRows++] = (byte)(indexedPixels[idxPixels++] << 4);
+                        rows4bit[idx4bitRows++] = (byte)(indexedPixelRow[idxPixels] << 4);
                     }
                 }
 
@@ -86,12 +88,28 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Writers
             }
             else
             {
-                compressor.CompressStrip(indexedPixels, height);
+                int stripPixels = width * height;
+                this.indexedPixelsBuffer ??= this.MemoryAllocator.AllocateManagedByteBuffer(stripPixels);
+                Span<byte> indexedPixels = this.indexedPixelsBuffer.GetSpan();
+                int lastRow = y + height;
+                int indexedPixelsRowIdx = 0;
+                for (int row = y; row < lastRow; row++)
+                {
+                    ReadOnlySpan<byte> indexedPixelRow = this.quantizedImage.GetPixelRowSpan(row);
+                    indexedPixelRow.CopyTo(indexedPixels.Slice(indexedPixelsRowIdx * width, width));
+                    indexedPixelsRowIdx++;
+                }
+
+                compressor.CompressStrip(indexedPixels.Slice(0, stripPixels), height);
             }
         }
 
         /// <inheritdoc />
-        protected override void Dispose(bool disposing) => this.quantizedImage?.Dispose();
+        protected override void Dispose(bool disposing)
+        {
+            this.quantizedImage?.Dispose(); 
+            this.indexedPixelsBuffer?.Dispose();
+        }
 
         private void AddColorMapTag()
         {