Include sizeof(T) in offset calculation for Memory2D from MemoryManager

src/CommunityToolkit.HighPerformance/Memory/Memory2D{T}.cs

@@ -338,7 +338,7 @@ public Memory2D(MemoryManager<T> memoryManager, int height, int width)
     /// <exception cref="ArgumentException">
     /// Thrown when the requested area is outside of bounds for <paramref name="memoryManager"/>.
     /// </exception>
-    public Memory2D(MemoryManager<T> memoryManager, int offset, int height, int width, int pitch)
+    public unsafe Memory2D(MemoryManager<T> memoryManager, int offset, int height, int width, int pitch)
     {
         int length = memoryManager.GetSpan().Length;
 
@@ -378,7 +378,7 @@ public Memory2D(MemoryManager<T> memoryManager, int offset, int height, int widt
         }
 
         this.instance = memoryManager;
-        this.offset = (nint)(uint)offset;
+        this.offset = (nint)(uint)offset * (nint)(uint)sizeof(T);
         this.height = height;
         this.width = width;
         this.pitch = pitch;
@@ -413,7 +413,7 @@ internal Memory2D(Memory<T> memory, int height, int width)
     /// <exception cref="ArgumentException">
     /// Thrown when the requested area is outside of bounds for <paramref name="memory"/>.
     /// </exception>
-    internal Memory2D(Memory<T> memory, int offset, int height, int width, int pitch)
+    internal unsafe Memory2D(Memory<T> memory, int offset, int height, int width, int pitch)
     {
         if ((uint)offset > (uint)memory.Length)
         {
@@ -477,7 +477,7 @@ internal Memory2D(Memory<T> memory, int offset, int height, int width, int pitch
         else if (MemoryMarshal.TryGetMemoryManager<T, MemoryManager<T>>(memory, out MemoryManager<T>? memoryManager, out int memoryManagerStart, out _))
         {
             this.instance = memoryManager;
-            this.offset = (nint)(uint)(memoryManagerStart + offset);
+            this.offset = (nint)(uint)(memoryManagerStart + offset) * (nint)(uint)sizeof(T);
         }
         else
         {

src/CommunityToolkit.HighPerformance/Memory/ReadOnlyMemory2D{T}.cs

@@ -358,7 +358,7 @@ public ReadOnlyMemory2D(MemoryManager<T> memoryManager, int height, int width)
     /// <exception cref="ArgumentException">
     /// Thrown when the requested area is outside of bounds for <paramref name="memoryManager"/>.
     /// </exception>
-    public ReadOnlyMemory2D(MemoryManager<T> memoryManager, int offset, int height, int width, int pitch)
+    public unsafe ReadOnlyMemory2D(MemoryManager<T> memoryManager, int offset, int height, int width, int pitch)
     {
         int length = memoryManager.GetSpan().Length;
 
@@ -398,7 +398,7 @@ public ReadOnlyMemory2D(MemoryManager<T> memoryManager, int offset, int height,
         }
 
         this.instance = memoryManager;
-        this.offset = (nint)(uint)offset;
+        this.offset = (nint)(uint)offset * (nint)(uint)sizeof(T);
         this.height = height;
         this.width = width;
         this.pitch = pitch;
@@ -433,7 +433,7 @@ internal ReadOnlyMemory2D(ReadOnlyMemory<T> memory, int height, int width)
     /// <exception cref="ArgumentException">
     /// Thrown when the requested area is outside of bounds for <paramref name="memory"/>.
     /// </exception>
-    internal ReadOnlyMemory2D(ReadOnlyMemory<T> memory, int offset, int height, int width, int pitch)
+    internal unsafe ReadOnlyMemory2D(ReadOnlyMemory<T> memory, int offset, int height, int width, int pitch)
     {
         if ((uint)offset > (uint)memory.Length)
         {
@@ -489,7 +489,7 @@ internal ReadOnlyMemory2D(ReadOnlyMemory<T> memory, int offset, int height, int
         else if (MemoryMarshal.TryGetMemoryManager(memory, out MemoryManager<T>? memoryManager, out int memoryManagerStart, out _))
         {
             this.instance = memoryManager;
-            this.offset = (nint)(uint)(memoryManagerStart + offset);
+            this.offset = (nint)(uint)(memoryManagerStart + offset) * (nint)(uint)sizeof(T);
         }
         else
         {

tests/CommunityToolkit.HighPerformance.UnitTests/Memory/Test_ReadOnlySpan2D{T}.cs

@@ -3,6 +3,9 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+#if NET6_0_OR_GREATER
+using System.Buffers;
+#endif
 using System.Runtime.CompilerServices;
 using CommunityToolkit.HighPerformance.Enumerables;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
@@ -1014,4 +1017,96 @@ public void Test_ReadOnlySpan2DT_ReadOnlyRefEnumerable_Cast()
 
         CollectionAssert.AreEqual(result, row);
     }
+
+#if NET6_0_OR_GREATER
+    [TestMethod]
+    public void Test_ReadOnlySpan2DT_FromMemoryManager_Indexing()
+    {
+        const int w = 10;
+        const int h = 10;
+        const int l = w * h;
+
+        byte[] b = new byte[l];
+        short[] s = new short[l];
+
+        for (int i = 0; i < l; ++i)
+        {
+            b[i] = (byte)i;
+            s[i] = (short)i;
+        }
+
+        Memory2DTester<byte> byteTester = new(w, h, b);
+        Span2D<byte> byteSpan2DFromArray = byteTester.GetMemory2DFromArray().Span;
+
+        Assert.AreEqual(11, byteSpan2DFromArray[0, 0]);
+
+        Span2D<byte> byteSpan2DFromMemoryManager = byteTester.GetMemory2DFromMemoryManager().Span;
+
+        Assert.AreEqual(11, byteSpan2DFromMemoryManager[0, 0]);
+
+        Memory2DTester<short> shortTester = new(w, h, s);
+        Span2D<short> shortSpan2DFromArray = shortTester.GetMemory2DFromArray().Span;
+        Span2D<short> shortSpan2DFromMemoryManager = shortTester.GetMemory2DFromMemoryManager().Span;
+
+        Assert.AreEqual(11, shortSpan2DFromArray[0, 0]);
+        Assert.AreEqual(11, shortSpan2DFromMemoryManager[0, 0]);
+    }
+#endif
 }
+
+#if NET6_0_OR_GREATER
+public sealed class Memory2DTester<T> : MemoryManager<T>
+    where T : unmanaged
+{
+    private readonly T[] data;
+
+    public Memory2DTester(int w, int h, T[] data)
+    {
+        if (w < 2 || h < 2)
+        {
+            throw new ArgumentException("The 'w' and 'h' arguments must be at least 2.");
+        }
+
+        this.data = data;
+
+        Width = w;
+        Height = h;
+    }
+
+    public int Width { get; }
+
+    public int Height { get; }
+
+    public Memory2D<T> GetMemory2DFromMemoryManager()
+    {
+        return new(this, Width + 1, Height - 1, Width - 1, 1);
+    }
+
+    public Memory2D<T> GetMemory2DFromArray()
+    {
+        return new(this.data, Width + 1, Height - 1, Width - 1, 1);
+    }
+
+    /// <inheritdoc/>
+    public override Span<T> GetSpan()
+    {
+        return new(this.data);
+    }
+
+    /// <inheritdoc/>
+    public override MemoryHandle Pin(int elementIndex = 0)
+    {
+        return default;
+    }
+
+    /// <inheritdoc/>
+    public override void Unpin()
+    {
+    }
+
+    /// <inheritdoc/>
+    protected override void Dispose(bool disposing)
+    {
+    }
+}
+#endif