Fix resize pad color application for non Nearest Neighbor samplers

src/ImageSharp/Processing/Extensions/Transforms/PadExtensions.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
+
 namespace SixLabors.ImageSharp.Processing
 {
     /// <summary>
@@ -29,9 +31,11 @@ public static IImageProcessingContext Pad(this IImageProcessingContext source, i
         /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
         public static IImageProcessingContext Pad(this IImageProcessingContext source, int width, int height, Color color)
         {
+            Size size = source.GetCurrentSize();
             var options = new ResizeOptions
             {
-                Size = new Size(width, height),
+                // Prevent downsizing.
+                Size = new Size(Math.Max(width, size.Width), Math.Max(height, size.Height)),
                 Mode = ResizeMode.BoxPad,
                 Sampler = KnownResamplers.NearestNeighbor,
                 PadColor = color

src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeKernelMap.cs

@@ -101,7 +101,7 @@ protected virtual void Dispose(bool disposing)
         /// Returns a <see cref="ResizeKernel"/> for an index value between 0 and DestinationSize - 1.
         /// </summary>
         [MethodImpl(InliningOptions.ShortMethod)]
-        internal ref ResizeKernel GetKernel(int destIdx) => ref this.kernels[destIdx];
+        internal ref ResizeKernel GetKernel(nint destIdx) => ref this.kernels[destIdx];
 
         /// <summary>
         /// Computes the weights to apply at each pixel when resizing.

src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeProcessor{TPixel}.cs

@@ -61,9 +61,9 @@ public void ApplyTransform<TResampler>(in TResampler sampler)
             Rectangle destinationRectangle = this.destinationRectangle;
             bool compand = this.options.Compand;
             bool premultiplyAlpha = this.options.PremultiplyAlpha;
+            TPixel fillColor = this.options.PadColor.ToPixel<TPixel>();
             bool shouldFill = (this.options.Mode == ResizeMode.BoxPad || this.options.Mode == ResizeMode.Pad)
                               && this.options.PadColor != default;
-            TPixel fillColor = this.options.PadColor.ToPixel<TPixel>();
 
             // Handle resize dimensions identical to the original
             if (source.Width == destination.Width
@@ -209,21 +209,18 @@ private static void ApplyResizeFrameTransform(
 
             // To reintroduce parallel processing, we would launch multiple workers
             // for different row intervals of the image.
-            using (var worker = new ResizeWorker<TPixel>(
+            using var worker = new ResizeWorker<TPixel>(
                 configuration,
                 sourceRegion,
                 conversionModifiers,
                 horizontalKernelMap,
                 verticalKernelMap,
-                destination.Width,
                 interest,
-                destinationRectangle.Location))
-            {
-                worker.Initialize();
+                destinationRectangle.Location);
+            worker.Initialize();
 
-                var workingInterval = new RowInterval(interest.Top, interest.Bottom);
-                worker.FillDestinationPixels(workingInterval, destination.PixelBuffer);
-            }
+            var workingInterval = new RowInterval(interest.Top, interest.Bottom);
+            worker.FillDestinationPixels(workingInterval, destination.PixelBuffer);
         }
 
         private readonly struct NNRowOperation : IRowOperation

src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeWorker.cs

@@ -39,8 +39,6 @@ internal sealed class ResizeWorker<TPixel> : IDisposable
 
         private readonly ResizeKernelMap verticalKernelMap;
 
-        private readonly int destWidth;
-
         private readonly Rectangle targetWorkingRect;
 
         private readonly Point targetOrigin;
@@ -57,7 +55,6 @@ public ResizeWorker(
             PixelConversionModifiers conversionModifiers,
             ResizeKernelMap horizontalKernelMap,
             ResizeKernelMap verticalKernelMap,
-            int destWidth,
             Rectangle targetWorkingRect,
             Point targetOrigin)
         {
@@ -67,7 +64,6 @@ public ResizeWorker(
             this.conversionModifiers = conversionModifiers;
             this.horizontalKernelMap = horizontalKernelMap;
             this.verticalKernelMap = verticalKernelMap;
-            this.destWidth = destWidth;
             this.targetWorkingRect = targetWorkingRect;
             this.targetOrigin = targetOrigin;
 
@@ -80,19 +76,19 @@ public ResizeWorker(
 
             int numberOfWindowBands = ResizeHelper.CalculateResizeWorkerHeightInWindowBands(
                 this.windowBandHeight,
-                destWidth,
+                targetWorkingRect.Width,
                 workingBufferLimitHintInBytes);
 
             this.workerHeight = Math.Min(this.sourceRectangle.Height, numberOfWindowBands * this.windowBandHeight);
 
             this.transposedFirstPassBuffer = configuration.MemoryAllocator.Allocate2D<Vector4>(
                 this.workerHeight,
-                destWidth,
+                targetWorkingRect.Width,
                 preferContiguosImageBuffers: true,
                 options: AllocationOptions.Clean);
 
             this.tempRowBuffer = configuration.MemoryAllocator.Allocate<Vector4>(this.sourceRectangle.Width);
-            this.tempColumnBuffer = configuration.MemoryAllocator.Allocate<Vector4>(destWidth);
+            this.tempColumnBuffer = configuration.MemoryAllocator.Allocate<Vector4>(targetWorkingRect.Width);
 
             this.currentWindow = new RowInterval(0, this.workerHeight);
         }
@@ -118,6 +114,9 @@ public void FillDestinationPixels(RowInterval rowInterval, Buffer2D<TPixel> dest
             // When creating transposedFirstPassBuffer, we made sure it's contiguous:
             Span<Vector4> transposedFirstPassBufferSpan = this.transposedFirstPassBuffer.DangerousGetSingleSpan();
 
+            int left = this.targetWorkingRect.Left;
+            int right = this.targetWorkingRect.Right;
+            int width = this.targetWorkingRect.Width;
             for (int y = rowInterval.Min; y < rowInterval.Max; y++)
             {
                 // Ensure offsets are normalized for cropping and padding.
@@ -131,17 +130,18 @@ public void FillDestinationPixels(RowInterval rowInterval, Buffer2D<TPixel> dest
                 ref Vector4 tempRowBase = ref MemoryMarshal.GetReference(tempColSpan);
 
                 int top = kernel.StartIndex - this.currentWindow.Min;
+
                 ref Vector4 fpBase = ref transposedFirstPassBufferSpan[top];
 
-                for (int x = 0; x < this.destWidth; x++)
+                for (nint x = left; x < right; x++)
                 {
-                    ref Vector4 firstPassColumnBase = ref Unsafe.Add(ref fpBase, x * this.workerHeight);
+                    ref Vector4 firstPassColumnBase = ref Unsafe.Add(ref fpBase, (x - left) * this.workerHeight);
 
                     // Destination color components
-                    Unsafe.Add(ref tempRowBase, x) = kernel.ConvolveCore(ref firstPassColumnBase);
+                    Unsafe.Add(ref tempRowBase, x - left) = kernel.ConvolveCore(ref firstPassColumnBase);
                 }
 
-                Span<TPixel> targetRowSpan = destination.DangerousGetRowSpan(y);
+                Span<TPixel> targetRowSpan = destination.DangerousGetRowSpan(y).Slice(left, width);
 
                 PixelOperations<TPixel>.Instance.FromVector4Destructive(this.configuration, tempColSpan, targetRowSpan, this.conversionModifiers);
             }
@@ -170,6 +170,8 @@ private void CalculateFirstPassValues(RowInterval calculationInterval)
             Span<Vector4> tempRowSpan = this.tempRowBuffer.GetSpan();
             Span<Vector4> transposedFirstPassBufferSpan = this.transposedFirstPassBuffer.DangerousGetSingleSpan();
 
+            int left = this.targetWorkingRect.Left;
+            int right = this.targetWorkingRect.Right;
             for (int y = calculationInterval.Min; y < calculationInterval.Max; y++)
             {
                 Span<TPixel> sourceRow = this.source.DangerousGetRowSpan(y);
@@ -184,13 +186,13 @@ private void CalculateFirstPassValues(RowInterval calculationInterval)
                 // Span<Vector4> firstPassSpan = transposedFirstPassBufferSpan.Slice(y - this.currentWindow.Min);
                 ref Vector4 firstPassBaseRef = ref transposedFirstPassBufferSpan[y - this.currentWindow.Min];
 
-                for (int x = this.targetWorkingRect.Left; x < this.targetWorkingRect.Right; x++)
+                for (nint x = left; x < right; x++)
                 {
                     ResizeKernel kernel = this.horizontalKernelMap.GetKernel(x - this.targetOrigin.X);
 
                     // optimization for:
                     // firstPassSpan[x * this.workerHeight] = kernel.Convolve(tempRowSpan);
-                    Unsafe.Add(ref firstPassBaseRef, x * this.workerHeight) = kernel.Convolve(tempRowSpan);
+                    Unsafe.Add(ref firstPassBaseRef, (x - left) * this.workerHeight) = kernel.Convolve(tempRowSpan);
                 }
             }
         }

tests/ImageSharp.Tests/Processing/Processors/Transforms/ResizeTests.cs

@@ -472,7 +472,8 @@ public void ResizeWithBoxPadMode<TPixel>(TestImageProvider<TPixel> provider)
                 var options = new ResizeOptions
                 {
                     Size = new Size(image.Width + 200, image.Height + 200),
-                    Mode = ResizeMode.BoxPad
+                    Mode = ResizeMode.BoxPad,
+                    PadColor = Color.HotPink
                 };
 
                 image.Mutate(x => x.Resize(options));
@@ -580,7 +581,8 @@ public void ResizeWithPadMode<TPixel>(TestImageProvider<TPixel> provider)
                 var options = new ResizeOptions
                 {
                     Size = new Size(image.Width + 200, image.Height),
-                    Mode = ResizeMode.Pad
+                    Mode = ResizeMode.Pad,
+                    PadColor = Color.Lavender
                 };
 
                 image.Mutate(x => x.Resize(options));