do not allocate unnecessaryly large buffer in WeightsBuffer

src/ImageSharp/Processing/Processors/Transforms/ResizeProcessor.cs

@@ -162,7 +162,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
 
             IResampler sampler = this.Sampler;
             float radius = MathF.Ceiling(scale * sampler.Radius);
-            var result = new WeightsBuffer(memoryAllocator, sourceSize, destinationSize);
+            var result = new WeightsBuffer(memoryAllocator, destinationSize, radius);
 
             for (int i = 0; i < destinationSize; i++)
             {

src/ImageSharp/Processing/Processors/Transforms/WeightsBuffer.cs

@@ -19,11 +19,12 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
         /// Initializes a new instance of the <see cref="WeightsBuffer"/> class.
         /// </summary>
         /// <param name="memoryAllocator">The <see cref="MemoryAllocator"/> to use for allocations.</param>
-        /// <param name="sourceSize">The size of the source window</param>
         /// <param name="destinationSize">The size of the destination window</param>
-        public WeightsBuffer(MemoryAllocator memoryAllocator, int sourceSize, int destinationSize)
+        /// <param name="kernelRadius">The radius of the kernel</param>
+        public WeightsBuffer(MemoryAllocator memoryAllocator, int destinationSize, float kernelRadius)
         {
-            this.dataBuffer = memoryAllocator.Allocate2D<float>(sourceSize, destinationSize, AllocationOptions.Clean);
+            int width = (int)Math.Ceiling(kernelRadius * 2);
+            this.dataBuffer = memoryAllocator.Allocate2D<float>(width, destinationSize, AllocationOptions.Clean);
             this.Weights = new WeightsWindow[destinationSize];
         }
 

src/ImageSharp/Processing/Processors/Transforms/WeightsWindow.cs

@@ -35,7 +35,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
         /// <summary>
         /// The buffer containing the weights values.
         /// </summary>
-        private readonly MemorySource<float> buffer;
+        private readonly Memory<float> buffer;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="WeightsWindow"/> struct.
@@ -47,9 +47,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal WeightsWindow(int index, int left, Buffer2D<float> buffer, int length)
         {
-            this.flatStartIndex = (index * buffer.Width) + left;
+            this.flatStartIndex = index * buffer.Width;
             this.Left = left;
-            this.buffer = buffer.MemorySource;
+            this.buffer = buffer.MemorySource.Memory;
             this.Length = length;
         }
 
@@ -60,7 +60,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public ref float GetStartReference()
         {
-            Span<float> span = this.buffer.GetSpan();
+            Span<float> span = this.buffer.Span;
             return ref span[this.flatStartIndex];
         }
 
@@ -69,7 +69,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
         /// </summary>
         /// <returns>The <see cref="Span{T}"/></returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public Span<float> GetWindowSpan() => this.buffer.GetSpan().Slice(this.flatStartIndex, this.Length);
+        public Span<float> GetWindowSpan() => this.buffer.Span.Slice(this.flatStartIndex, this.Length);
 
         /// <summary>
         /// Computes the sum of vectors in 'rowSpan' weighted by weight values, pointed by this <see cref="WeightsWindow"/> instance.