Improved performance of GifDecoder.

src/ImageSharp/Formats/Gif/GifDecoderCore.cs

@@ -356,8 +356,6 @@ namespace ImageSharp.Formats
             int interlaceY = 0; // The current interlaced line
 
             using (PixelAccessor<TColor> pixelAccessor = image.Lock())
-            {
-                using (PixelArea<TColor> pixelRow = new PixelArea<TColor>(imageWidth, ComponentOrder.XYZW))
             {
                 for (int y = descriptor.Top; y < descriptor.Top + descriptor.Height; y++)
                 {
@@ -396,10 +394,7 @@ namespace ImageSharp.Formats
                         writeY = y;
                     }
 
-                        pixelAccessor.CopyTo(pixelRow, writeY, descriptor.Left);
+                    for (int x = descriptor.Left; x < descriptor.Left + descriptor.Width; x++)
-
-                        byte* pixelBase = pixelRow.PixelBase;
-                        for (int x = 0; x < descriptor.Width; x++)
                     {
                         int index = indices[i];
 
@@ -408,23 +403,13 @@ namespace ImageSharp.Formats
                             this.graphicsControlExtension.TransparencyIndex != index)
                         {
                             int indexOffset = index * 3;
-                                *(pixelBase + 0) = colorTable[indexOffset];
-                                *(pixelBase + 1) = colorTable[indexOffset + 1];
-                                *(pixelBase + 2) = colorTable[indexOffset + 2];
-                                *(pixelBase + 3) = 255;
 
-                                // TODO: This is actually 200us faster in benchmarking.
+                            TColor pixel = default(TColor);
-                                // int indexOffset = index * 3;
+                            pixel.PackFromBytes(colorTable[indexOffset], colorTable[indexOffset + 1], colorTable[indexOffset + 2], 255);
-                                // TColor pixel = default(TColor);
+                            pixelAccessor[x, writeY] = pixel;
-                                // pixel.PackFromBytes(colorTable[indexOffset], colorTable[indexOffset + 1], colorTable[indexOffset + 2], 255);
-                                // currentPixels[x, writeY] = pixel;
                         }
 
                         i++;
-                            pixelBase += 4;
-                        }
-
-                        pixelAccessor.CopyFrom(pixelRow, writeY, descriptor.Left);
                     }
                 }
             }