Eliminate AV1 scalar predictor allocations

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1DcFillPredictor.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// <summary>
 /// Predicts an 8-bit AV1 block with the sample-domain midpoint when neither top nor left neighbors are available.
 /// </summary>
-internal class Av1DcFillPredictor : IAv1Predictor
+internal readonly struct Av1DcFillPredictor : IAv1Predictor
 {
     /// <summary>
     /// The number of samples written to each destination row.
@@ -22,7 +22,7 @@ internal class Av1DcFillPredictor : IAv1Predictor
     private readonly uint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DcFillPredictor"/> class for explicit block dimensions.
+    /// Initializes a new instance of the <see cref="Av1DcFillPredictor"/> struct for explicit block dimensions.
     /// </summary>
     /// <param name="blockSize">The predicted block dimensions in samples.</param>
     public Av1DcFillPredictor(Size blockSize)
@@ -32,7 +32,7 @@ internal class Av1DcFillPredictor : IAv1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DcFillPredictor"/> class for a transform size.
+    /// Initializes a new instance of the <see cref="Av1DcFillPredictor"/> struct for a transform size.
     /// </summary>
     /// <param name="transformSize">The transform size whose dimensions define the predicted block.</param>
     public Av1DcFillPredictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1DcLeftPredictor.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// <summary>
 /// Predicts an 8-bit AV1 block from the rounded average of its available left neighboring samples.
 /// </summary>
-internal class Av1DcLeftPredictor : IAv1Predictor
+internal readonly struct Av1DcLeftPredictor : IAv1Predictor
 {
     /// <summary>
     /// The number of samples written to each destination row.
@@ -22,7 +22,7 @@ internal class Av1DcLeftPredictor : IAv1Predictor
     private readonly uint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DcLeftPredictor"/> class for explicit block dimensions.
+    /// Initializes a new instance of the <see cref="Av1DcLeftPredictor"/> struct for explicit block dimensions.
     /// </summary>
     /// <param name="blockSize">The predicted block dimensions in samples.</param>
     public Av1DcLeftPredictor(Size blockSize)
@@ -32,7 +32,7 @@ internal class Av1DcLeftPredictor : IAv1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DcLeftPredictor"/> class for a transform size.
+    /// Initializes a new instance of the <see cref="Av1DcLeftPredictor"/> struct for a transform size.
     /// </summary>
     /// <param name="transformSize">The transform size whose dimensions define the predicted block.</param>
     public Av1DcLeftPredictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1DcPredictor.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// <summary>
 /// Predicts an 8-bit AV1 block from the rounded average of its top and left neighboring samples.
 /// </summary>
-internal class Av1DcPredictor : IAv1Predictor
+internal readonly struct Av1DcPredictor : IAv1Predictor
 {
     /// <summary>
     /// The number of top samples averaged and samples written to each destination row.
@@ -22,7 +22,7 @@ internal class Av1DcPredictor : IAv1Predictor
     private readonly nuint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DcPredictor"/> class for explicit block dimensions.
+    /// Initializes a new instance of the <see cref="Av1DcPredictor"/> struct for explicit block dimensions.
     /// </summary>
     /// <param name="blockSize">The predicted block dimensions in samples.</param>
     public Av1DcPredictor(Size blockSize)
@@ -32,7 +32,7 @@ internal class Av1DcPredictor : IAv1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DcPredictor"/> class for a transform size.
+    /// Initializes a new instance of the <see cref="Av1DcPredictor"/> struct for a transform size.
     /// </summary>
     /// <param name="transformSize">The transform size whose dimensions define the predicted block.</param>
     public Av1DcPredictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1DcTopPredictor.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// <summary>
 /// Predicts an 8-bit AV1 block from the rounded average of its available top neighboring samples.
 /// </summary>
-internal class Av1DcTopPredictor : IAv1Predictor
+internal readonly struct Av1DcTopPredictor : IAv1Predictor
 {
     /// <summary>
     /// The number of top samples averaged and samples written to each destination row.
@@ -22,7 +22,7 @@ internal class Av1DcTopPredictor : IAv1Predictor
     private readonly uint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DcTopPredictor"/> class for explicit block dimensions.
+    /// Initializes a new instance of the <see cref="Av1DcTopPredictor"/> struct for explicit block dimensions.
     /// </summary>
     /// <param name="blockSize">The predicted block dimensions in samples.</param>
     public Av1DcTopPredictor(Size blockSize)
@@ -32,7 +32,7 @@ internal class Av1DcTopPredictor : IAv1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DcTopPredictor"/> class for a transform size.
+    /// Initializes a new instance of the <see cref="Av1DcTopPredictor"/> struct for a transform size.
     /// </summary>
     /// <param name="transformSize">The transform size whose dimensions define the predicted block.</param>
     public Av1DcTopPredictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1DirectionalZone1Predictor.cs

@@ -13,7 +13,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// Zone 1 projects the top reference samples into the block for prediction angles less than 90 degrees.
 /// The scalar prediction follows the directional prediction process in section 7.11.2.4 of the AV1 specification.
 /// </remarks>
-internal class Av1DirectionalZone1Predictor
+internal readonly struct Av1DirectionalZone1Predictor
 {
     /// <summary>
     /// The width of the prediction block in samples.
@@ -26,7 +26,7 @@ internal class Av1DirectionalZone1Predictor
     private readonly nuint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DirectionalZone1Predictor"/> class for the specified block dimensions.
+    /// Initializes a new instance of the <see cref="Av1DirectionalZone1Predictor"/> struct for the specified block dimensions.
     /// </summary>
     /// <param name="blockSize">The dimensions of the prediction block.</param>
     public Av1DirectionalZone1Predictor(Size blockSize)
@@ -36,7 +36,7 @@ internal class Av1DirectionalZone1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DirectionalZone1Predictor"/> class for the specified transform size.
+    /// Initializes a new instance of the <see cref="Av1DirectionalZone1Predictor"/> struct for the specified transform size.
     /// </summary>
     /// <param name="transformSize">The transform size that determines the prediction block dimensions.</param>
     public Av1DirectionalZone1Predictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1DirectionalZone2Predictor.cs

@@ -15,7 +15,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// Zone 2 projects both top and left reference samples into the block for prediction angles between 90 and 180 degrees.
 /// The scalar prediction follows the directional prediction process in section 7.11.2.4 of the AV1 specification.
 /// </remarks>
-internal class Av1DirectionalZone2Predictor
+internal readonly struct Av1DirectionalZone2Predictor
 {
     /// <summary>
     /// The width of the prediction block in samples.
@@ -28,7 +28,7 @@ internal class Av1DirectionalZone2Predictor
     private readonly nuint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DirectionalZone2Predictor"/> class for the specified block dimensions.
+    /// Initializes a new instance of the <see cref="Av1DirectionalZone2Predictor"/> struct for the specified block dimensions.
     /// </summary>
     /// <param name="blockSize">The dimensions of the prediction block.</param>
     public Av1DirectionalZone2Predictor(Size blockSize)
@@ -38,7 +38,7 @@ internal class Av1DirectionalZone2Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DirectionalZone2Predictor"/> class for the specified transform size.
+    /// Initializes a new instance of the <see cref="Av1DirectionalZone2Predictor"/> struct for the specified transform size.
     /// </summary>
     /// <param name="transformSize">The transform size that determines the prediction block dimensions.</param>
     public Av1DirectionalZone2Predictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1DirectionalZone3Predictor.cs

@@ -14,7 +14,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// Zone 3 projects the left reference samples into the block for prediction angles greater than 180 degrees.
 /// The scalar prediction follows the directional prediction process in section 7.11.2.4 of the AV1 specification.
 /// </remarks>
-internal class Av1DirectionalZone3Predictor
+internal readonly struct Av1DirectionalZone3Predictor
 {
     /// <summary>
     /// The width of the prediction block in samples.
@@ -27,7 +27,7 @@ internal class Av1DirectionalZone3Predictor
     private readonly nuint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DirectionalZone3Predictor"/> class for the specified block dimensions.
+    /// Initializes a new instance of the <see cref="Av1DirectionalZone3Predictor"/> struct for the specified block dimensions.
     /// </summary>
     /// <param name="blockSize">The dimensions of the prediction block.</param>
     public Av1DirectionalZone3Predictor(Size blockSize)
@@ -37,7 +37,7 @@ internal class Av1DirectionalZone3Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1DirectionalZone3Predictor"/> class for the specified transform size.
+    /// Initializes a new instance of the <see cref="Av1DirectionalZone3Predictor"/> struct for the specified transform size.
     /// </summary>
     /// <param name="transformSize">The transform size that determines the prediction block dimensions.</param>
     public Av1DirectionalZone3Predictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1HorizontalPredictor.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// <summary>
 /// Predicts an 8-bit AV1 block by extending each left neighboring sample across its destination row.
 /// </summary>
-internal class Av1HorizontalPredictor : IAv1Predictor
+internal readonly struct Av1HorizontalPredictor : IAv1Predictor
 {
     /// <summary>
     /// The number of samples written to each destination row.
@@ -22,7 +22,7 @@ internal class Av1HorizontalPredictor : IAv1Predictor
     private readonly nuint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1HorizontalPredictor"/> class for explicit block dimensions.
+    /// Initializes a new instance of the <see cref="Av1HorizontalPredictor"/> struct for explicit block dimensions.
     /// </summary>
     /// <param name="blockSize">The predicted block dimensions in samples.</param>
     public Av1HorizontalPredictor(Size blockSize)
@@ -32,7 +32,7 @@ internal class Av1HorizontalPredictor : IAv1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1HorizontalPredictor"/> class for a transform size.
+    /// Initializes a new instance of the <see cref="Av1HorizontalPredictor"/> struct for a transform size.
     /// </summary>
     /// <param name="transformSize">The transform size whose dimensions define the predicted block.</param>
     public Av1HorizontalPredictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1PaethPredictor.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// <summary>
 /// Predicts an 8-bit AV1 block by selecting the top, left, or top-left neighbor with the smallest local gradient.
 /// </summary>
-internal class Av1PaethPredictor : IAv1Predictor
+internal readonly struct Av1PaethPredictor : IAv1Predictor
 {
     /// <summary>
     /// The number of top samples consumed and samples written to each destination row.
@@ -22,7 +22,7 @@ internal class Av1PaethPredictor : IAv1Predictor
     private readonly uint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1PaethPredictor"/> class for explicit block dimensions.
+    /// Initializes a new instance of the <see cref="Av1PaethPredictor"/> struct for explicit block dimensions.
     /// </summary>
     /// <param name="blockSize">The predicted block dimensions in samples.</param>
     public Av1PaethPredictor(Size blockSize)
@@ -32,7 +32,7 @@ internal class Av1PaethPredictor : IAv1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1PaethPredictor"/> class for a transform size.
+    /// Initializes a new instance of the <see cref="Av1PaethPredictor"/> struct for a transform size.
     /// </summary>
     /// <param name="transformSize">The transform size whose dimensions define the predicted block.</param>
     public Av1PaethPredictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1SmoothHorizontalPredictor.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// <summary>
 /// Predicts an 8-bit AV1 block by smoothly blending each left neighbor toward the top-right reference sample.
 /// </summary>
-internal class Av1SmoothHorizontalPredictor : IAv1Predictor
+internal readonly struct Av1SmoothHorizontalPredictor : IAv1Predictor
 {
     /// <summary>
     /// The number of interpolation weights and samples written to each destination row.
@@ -22,7 +22,7 @@ internal class Av1SmoothHorizontalPredictor : IAv1Predictor
     private readonly nuint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1SmoothHorizontalPredictor"/> class for explicit block dimensions.
+    /// Initializes a new instance of the <see cref="Av1SmoothHorizontalPredictor"/> struct for explicit block dimensions.
     /// </summary>
     /// <param name="blockSize">The predicted block dimensions in samples.</param>
     public Av1SmoothHorizontalPredictor(Size blockSize)
@@ -32,7 +32,7 @@ internal class Av1SmoothHorizontalPredictor : IAv1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1SmoothHorizontalPredictor"/> class for a transform size.
+    /// Initializes a new instance of the <see cref="Av1SmoothHorizontalPredictor"/> struct for a transform size.
     /// </summary>
     /// <param name="transformSize">The transform size whose dimensions define the predicted block.</param>
     public Av1SmoothHorizontalPredictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1SmoothPredictor.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// <summary>
 /// Predicts an 8-bit AV1 block by blending top-to-bottom and left-to-right smooth interpolation surfaces.
 /// </summary>
-internal class Av1SmoothPredictor : IAv1Predictor
+internal readonly struct Av1SmoothPredictor : IAv1Predictor
 {
     // Weights are quadratic from '1' to '1 / BlockSize', scaled by
     // 2^sm_weight_log2_scale.
@@ -61,7 +61,7 @@ internal class Av1SmoothPredictor : IAv1Predictor
     private readonly nuint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1SmoothPredictor"/> class for explicit block dimensions.
+    /// Initializes a new instance of the <see cref="Av1SmoothPredictor"/> struct for explicit block dimensions.
     /// </summary>
     /// <param name="blockSize">The predicted block dimensions in samples.</param>
     public Av1SmoothPredictor(Size blockSize)
@@ -71,7 +71,7 @@ internal class Av1SmoothPredictor : IAv1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1SmoothPredictor"/> class for a transform size.
+    /// Initializes a new instance of the <see cref="Av1SmoothPredictor"/> struct for a transform size.
     /// </summary>
     /// <param name="transformSize">The transform size whose dimensions define the predicted block.</param>
     public Av1SmoothPredictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1SmoothVerticalPredictor.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// <summary>
 /// Predicts an 8-bit AV1 block by smoothly blending each top neighbor toward the bottom-left reference sample.
 /// </summary>
-internal class Av1SmoothVerticalPredictor : IAv1Predictor
+internal readonly struct Av1SmoothVerticalPredictor : IAv1Predictor
 {
     /// <summary>
     /// The number of top samples consumed and samples written to each destination row.
@@ -22,7 +22,7 @@ internal class Av1SmoothVerticalPredictor : IAv1Predictor
     private readonly nuint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1SmoothVerticalPredictor"/> class for explicit block dimensions.
+    /// Initializes a new instance of the <see cref="Av1SmoothVerticalPredictor"/> struct for explicit block dimensions.
     /// </summary>
     /// <param name="blockSize">The predicted block dimensions in samples.</param>
     public Av1SmoothVerticalPredictor(Size blockSize)
@@ -32,7 +32,7 @@ internal class Av1SmoothVerticalPredictor : IAv1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1SmoothVerticalPredictor"/> class for a transform size.
+    /// Initializes a new instance of the <see cref="Av1SmoothVerticalPredictor"/> struct for a transform size.
     /// </summary>
     /// <param name="transformSize">The transform size whose dimensions define the predicted block.</param>
     public Av1SmoothVerticalPredictor(Av1TransformSize transformSize)

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1VerticalPredictor.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Prediction;
 /// <summary>
 /// Predicts an 8-bit AV1 block by copying the top neighboring samples into every destination row.
 /// </summary>
-internal class Av1VerticalPredictor : IAv1Predictor
+internal readonly struct Av1VerticalPredictor : IAv1Predictor
 {
     /// <summary>
     /// The number of top samples consumed and samples written to each destination row.
@@ -22,7 +22,7 @@ internal class Av1VerticalPredictor : IAv1Predictor
     private readonly nuint blockHeight;
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1VerticalPredictor"/> class for explicit block dimensions.
+    /// Initializes a new instance of the <see cref="Av1VerticalPredictor"/> struct for explicit block dimensions.
     /// </summary>
     /// <param name="blockSize">The predicted block dimensions in samples.</param>
     public Av1VerticalPredictor(Size blockSize)
@@ -32,7 +32,7 @@ internal class Av1VerticalPredictor : IAv1Predictor
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="Av1VerticalPredictor"/> class for a transform size.
+    /// Initializes a new instance of the <see cref="Av1VerticalPredictor"/> struct for a transform size.
     /// </summary>
     /// <param name="transformSize">The transform size whose dimensions define the predicted block.</param>
     public Av1VerticalPredictor(Av1TransformSize transformSize)