better docs, drop PixelExtensions, fix tests

src/ImageSharp/PixelFormats/Utils/PixelConverter.cs

@@ -12,7 +12,9 @@ namespace SixLabors.ImageSharp.PixelFormats.Utils
     /// <remarks>
     /// Implementations are based on ideas in:
     /// https://github.com/dotnet/coreclr/blob/master/src/System.Private.CoreLib/shared/System/Buffers/Binary/Reader.cs#L84
-    /// The JIT should be able to detect and optimize ROL and ROR patterns.
+    /// The JIT can detect and optimize rotation idioms ROTL (Rotate Left)
+    /// and ROTR (Rotate Right) emitting efficient CPU instructions:
+    /// https://github.com/dotnet/coreclr/pull/1830
     /// </remarks>
     internal static class PixelConverter
     {
@@ -25,7 +27,7 @@ namespace SixLabors.ImageSharp.PixelFormats.Utils
             public static uint ToArgb32(uint packedRgba)
             {
                 // packedRgba          = [aa bb gg rr]
-                // ROL(8, packedRgba)  = [bb gg rr aa]
+                // ROTL(8, packedRgba) = [bb gg rr aa]
                 return (packedRgba << 8) | (packedRgba >> 24);
             }
 
@@ -38,7 +40,7 @@ namespace SixLabors.ImageSharp.PixelFormats.Utils
                 // packedRgba          = [aa bb gg rr]
                 // tmp1                = [aa 00 gg 00]
                 // tmp2                = [00 bb 00 rr]
-                // tmp3=ROL(16, tmp2)  = [00 rr 00 bb]
+                // tmp3=ROTL(16, tmp2)  = [00 rr 00 bb]
                 // tmp1 + tmp3         = [aa rr gg bb]
                 uint tmp1 = packedRgba & 0xFF00FF00;
                 uint tmp2 = packedRgba & 0x00FF00FF;
@@ -56,7 +58,7 @@ namespace SixLabors.ImageSharp.PixelFormats.Utils
             public static uint ToRgba32(uint packedArgb)
             {
                 // packedArgb          = [bb gg rr aa]
-                // ROR(8, packedArgb)  = [aa bb gg rr]
+                // ROTR(8, packedArgb) = [aa bb gg rr]
                 return (packedArgb >> 8) | (packedArgb << 24);
             }
 
@@ -94,7 +96,7 @@ namespace SixLabors.ImageSharp.PixelFormats.Utils
                 // packedRgba          = [aa rr gg bb]
                 // tmp1                = [aa 00 gg 00]
                 // tmp2                = [00 rr 00 bb]
-                // tmp3=ROL(16, tmp2)  = [00 bb 00 rr]
+                // tmp3=ROTL(16, tmp2) = [00 bb 00 rr]
                 // tmp1 + tmp3         = [aa bb gg rr]
                 uint tmp1 = packedBgra & 0xFF00FF00;
                 uint tmp2 = packedBgra & 0x00FF00FF;

src/ImageSharp/PixelFormats/Utils/PixelExtensions.cs

@@ -1,22 +0,0 @@
-// Copyright (c) Six Labors and contributors.
-// Licensed under the Apache License, Version 2.0.
-
-namespace SixLabors.ImageSharp.PixelFormats.Utils
-{
-    /// <summary>
-    /// Low-performance extension methods to help conversion syntax, suitable for testing purposes.
-    /// </summary>
-    internal static class PixelExtensions
-    {
-        /// <summary>
-        /// Returns the result of <see cref="IPixel.ToRgba32"/> as a new <see cref="Rgba32"/> instance.
-        /// </summary>
-        public static Rgba32 ToRgba32<TPixel>(this TPixel pixel)
-            where TPixel : struct, IPixel<TPixel>
-        {
-            Rgba32 result = default;
-            pixel.ToRgba32(ref result);
-            return result;
-        }
-    }
-}

tests/ImageSharp.Tests/Drawing/FillLinearGradientBrushTests.cs

@@ -328,7 +328,9 @@ namespace SixLabors.ImageSharp.Tests.Drawing
                 TPixel color = colors[stopColorCodes[i % colors.Length]];
                 float position = stopPositions[i];
                 colorStops[i] = new ColorStop<TPixel>(position, color);
-                coloringVariant.AppendFormat(CultureInfo.InvariantCulture, "{0}@{1};", color.ToRgba32().ToHex(), position);
+                Rgba32 rgba = default;
+                color.ToRgba32(ref rgba);
+                coloringVariant.AppendFormat(CultureInfo.InvariantCulture, "{0}@{1};", rgba.ToHex(), position);
             }
 
             FormattableString variant = $"({startX},{startY})_TO_({endX},{endY})__[{coloringVariant}]";

tests/ImageSharp.Tests/PixelFormats/Alpha8Tests.cs

@@ -90,7 +90,8 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
             var input = new Alpha8(128);
             var expected = new Rgba32(0, 0, 0, 128);
 
-            var actual = input.ToRgba32();
+            Rgba32 actual = default;
+            input.ToRgba32(ref actual);
             Assert.Equal(expected, actual);
         }
     }

tests/ImageSharp.Tests/PixelFormats/Gray16Tests.cs

@@ -117,7 +117,8 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
             var gray = new Gray16(input);
 
             // Act
-            var actual = gray.ToRgba32();
+            Rgba32 actual = default;
+            gray.ToRgba32(ref actual);
 
             // Assert
             Assert.Equal(expected, actual.R);

tests/ImageSharp.Tests/PixelFormats/Gray8Tests.cs

@@ -115,10 +115,11 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
             var gray = new Gray8(input);
 
             // Act
-            var actual = gray.ToRgba32();
+            Rgba32 actual = default;
+            gray.ToRgba32(ref actual);
 
             // Assert
-            Assert.Equal(input, actual.R);
+            Assert.Equal(input, actual.R); 
             Assert.Equal(input, actual.G);
             Assert.Equal(input, actual.B);
             Assert.Equal(byte.MaxValue, actual.A);

tests/ImageSharp.Tests/PixelFormats/Rgb24Tests.cs

@@ -104,7 +104,8 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
         public void ToRgba32()
         {
             var rgb = new Rgb24(1, 2, 3);
-            var rgba = rgb.ToRgba32();
+            Rgba32 rgba = default;
+            rgb.ToRgba32(ref rgba);
 
             Assert.Equal(new Rgba32(1, 2, 3, 255), rgba);
         }

tests/ImageSharp.Tests/PixelFormats/Rgb48Tests.cs

@@ -52,7 +52,8 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
             var expected = new Rgba32(20, 38, 76, 255);
 
             // act
-            var actual = rgba48.ToRgba32();
+            Rgba32 actual = default;
+            rgba48.ToRgba32(ref actual);
 
             // assert
             Assert.Equal(expected, actual);

tests/ImageSharp.Tests/PixelFormats/Rgba1010102Tests.cs

@@ -79,7 +79,8 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
             var expected = new Rgba32(25, 0, 128, 0);
 
             // act
-            var actual = rgba.ToRgba32();
+            Rgba32 actual = default;
+            rgba.ToRgba32(ref actual);
 
             // assert
             Assert.Equal(expected, actual);

tests/ImageSharp.Tests/PixelFormats/Rgba64Tests.cs

@@ -86,7 +86,7 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
             var expected = new Rgba32(20, 38, 76, 115);
 
             // act
-            actual = rgba64.ToRgba32();
+            rgba64.ToRgba32(ref actual);
 
             // assert
             Assert.Equal(expected, actual);

tests/ImageSharp.Tests/PixelFormats/Short2Tests.cs

@@ -88,7 +88,7 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
             var expected = new Rgba32(128, 127, 0, 255);
 
             // act
-            actual = short2.ToRgba32();
+            short2.ToRgba32(ref actual);
 
             // assert
             Assert.Equal(expected, actual);
@@ -104,7 +104,7 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
 
             // act 
             short2.FromRgba32(expected);
-            actual = short2.ToRgba32();
+            short2.ToRgba32(ref actual);
 
             // assert
             Assert.Equal(expected, actual);

tests/ImageSharp.Tests/PixelFormats/Short4Tests.cs

@@ -92,7 +92,7 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
             var expected = new Rgba32(172, 177, 243, 128);
 
             // act
-            actual = shortValue.ToRgba32();
+            shortValue.ToRgba32(ref actual);
 
             // assert
             Assert.Equal(expected, actual);
@@ -108,7 +108,7 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
 
             // act 
             short4.FromRgba32(expected);
-            actual = short4.ToRgba32();
+            short4.ToRgba32(ref actual);
 
             // assert
             Assert.Equal(expected, actual);
@@ -124,7 +124,9 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
 
             // act 
             short4.FromBgra32(expected);
-            actual.FromRgba32(short4.ToRgba32());
+            Rgba32 temp = default;
+            short4.ToRgba32(ref temp);
+            actual.FromRgba32(temp);
 
             // assert
             Assert.Equal(expected, actual);
@@ -140,7 +142,9 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats
 
             // act 
             short4.FromArgb32(expected);
-            actual.FromRgba32(short4.ToRgba32());
+            Rgba32 temp = default;
+            short4.ToRgba32(ref temp);
+            actual.FromRgba32(temp);
 
             // assert
             Assert.Equal(expected, actual);

tests/ImageSharp.Tests/PixelFormats/UnPackedPixelTests.cs

@@ -84,8 +84,10 @@ namespace SixLabors.ImageSharp.Tests.Colors
             var color = new Rgba32(24, 48, 96, 192);
             var colorVector = new RgbaVector(24 / 255F, 48 / 255F, 96 / 255F, 192 / 255F);
 
-            var rgba = color.ToRgba32();
+            Rgba32 rgba = default;
-            var rgbaVector = colorVector.ToRgba32();
+            Rgba32 rgbaVector = default;
+            color.ToRgba32(ref rgba);
+            colorVector.ToRgba32(ref rgbaVector);
 
             Assert.Equal(rgba, rgbaVector);
         }

tests/ImageSharp.Tests/Quantization/QuantizedImageTests.cs

@@ -106,9 +106,10 @@ namespace SixLabors.ImageSharp.Tests
         {
             // Transparent pixels are much more likely to be found at the end of a palette
             int index = -1;
+            Rgba32 trans = default;
             for (int i = quantized.Palette.Length - 1; i >= 0; i--)
             {
-                var trans = quantized.Palette[i].ToRgba32();
+                quantized.Palette[i].ToRgba32(ref trans);
 
                 if (trans.Equals(default))
                 {

tests/ImageSharp.Tests/TestUtilities/TestUtils.cs

@@ -80,8 +80,11 @@ namespace SixLabors.ImageSharp.Tests
                     }
                     else
                     {
-                        rgb1 = ca.ToRgba32().Rgb;
+                        Rgba32 rgba = default;
-                        rgb2 = cb.ToRgba32().Rgb;
+                        ca.ToRgba32(ref rgba);
+                        rgb1 = rgba.Rgb;
+                        cb.ToRgba32(ref rgba);
+                        rgb2 = rgba.Rgb;
 
                         if (!rgb1.Equals(rgb2))
                         {

tests/ImageSharp.Tests/TestUtilities/Tests/TestImageProviderTests.cs

@@ -275,11 +275,12 @@ namespace SixLabors.ImageSharp.Tests
             Assert.Equal(20, img.Height);
 
             Buffer2D<TPixel> pixels = img.GetRootFramePixelBuffer();
+            Rgba32 rgba = default;
             for (int y = 0; y < pixels.Height; y++)
             {
                 for (int x = 0; x < pixels.Width; x++)
                 {
-                    var rgba = pixels[x, y].ToRgba32();
+                    pixels[x, y].ToRgba32(ref rgba);
 
                     Assert.Equal(255, rgba.R);
                     Assert.Equal(100, rgba.G);