Minor performance refactorings.

Moved the division out of the loop, division is expensive.

src/ImageSharp.Drawing/Processing/Drawing/Processors/FillRegionProcessor.cs

@@ -100,6 +100,8 @@ namespace SixLabors.ImageSharp.Processing.Drawing.Processors
                 using (BasicArrayBuffer<float> scanline = source.MemoryManager.AllocateFake<float>(scanlineWidth))
                 {
                     bool scanlineDirty = true;
+                    float subpixelFraction = 1f / subpixelCount;
+                    float subpixelFractionPoint = subpixelFraction / subpixelCount;
                     for (int y = minY; y < maxY; y++)
                     {
                         if (scanlineDirty)
@@ -113,9 +115,8 @@ namespace SixLabors.ImageSharp.Processing.Drawing.Processors
                             scanlineDirty = false;
                         }
 
-                        float subpixelFraction = 1f / subpixelCount;
+                        float yPlusOne = y + 1;
-                        float subpixelFractionPoint = subpixelFraction / subpixelCount;
+                        for (float subPixel = (float)y; subPixel < yPlusOne; subPixel += subpixelFraction)
-                        for (float subPixel = (float)y; subPixel < y + 1; subPixel += subpixelFraction)
                         {
                             int pointsFound = region.Scan(subPixel + offset, buffer.Array, 0);
                             if (pointsFound == 0)
@@ -197,8 +198,7 @@ namespace SixLabors.ImageSharp.Processing.Drawing.Processors
 
         private static void QuickSort(Span<float> data)
         {
-            int hi = Math.Min(data.Length - 1, data.Length - 1);
+            QuickSort(data, 0, data.Length - 1);
-            QuickSort(data, 0, hi);
         }
 
         private static void QuickSort(Span<float> data, int lo, int hi)

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -321,9 +321,6 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <returns>The <see cref="T:byte[]"/></returns>
         private IManagedByteBuffer GetOptimalFilteredScanline()
         {
-            Span<byte> scanSpan = this.rawScanline.Span;
-            Span<byte> prevSpan = this.previousScanline.Span;
-
             // Palette images don't compress well with adaptive filtering.
             if (this.pngColorType == PngColorType.Palette || this.bitDepth < 8)
             {
@@ -331,6 +328,9 @@ namespace SixLabors.ImageSharp.Formats.Png
                 return this.result;
             }
 
+            Span<byte> scanSpan = this.rawScanline.Span;
+            Span<byte> prevSpan = this.previousScanline.Span;
+
             // This order, while different to the enumerated order is more likely to produce a smaller sum
             // early on which shaves a couple of milliseconds off the processing time.
             UpFilter.Encode(scanSpan, prevSpan, this.up.Span, out int currentSum);