attempting to fix accessors with missing BufferView [WIP]

Author: vpenades

src/SharpGLTF.Core/Memory/IAccessorArray.cs

@@ -0,0 +1,108 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace SharpGLTF.Memory
+{
+    /// <summary>
+    /// Represents a readable and sometimes writeable(*) array of elements
+    /// </summary>
+    /// <typeparam name="T">
+    /// For Index Buffers: <see cref="UInt32"/><br/>
+    /// For Vertex Buffers: <see cref="System.Numerics.Vector2"/>, <see cref="System.Numerics.Vector3"/>, <see cref="System.Numerics.Vector4"/> and so on.<br/>
+    /// For animations and other plain data: <see cref="float"/>, <see cref="System.Numerics.Quaternion"/>, <see cref="System.Numerics.Quaternion"/> and so on.<br/>
+    /// </typeparam>
+    /// <remarks>
+    /// <para>
+    /// This interface is exposed by <see cref="Schema2.Accessor"/> to easily encode/decode packed and strided elements
+    /// </para>
+    /// <para>
+    /// Implemented by:<br/>
+    /// <see cref="SparseArray{T}"/> (Read Only)<br/>
+    /// <see cref="IntegerArray"/><br/>
+    /// <see cref="ScalarArray"/><br/>
+    /// <see cref="Vector2Array"/><br/>
+    /// <see cref="Vector3Array"/><br/>
+    /// <see cref="Vector4Array"/><br/>
+    /// <see cref="QuaternionArray"/><br/>
+    /// <see cref="Matrix2x2Array"/><br/>
+    /// <see cref="Matrix3x2Array"/><br/>
+    /// <see cref="Matrix3x3Array"/><br/>
+    /// <see cref="Matrix4x3Array"/><br/>
+    /// <see cref="Matrix4x3Array"/><br/>
+    /// </para>
+    /// </remarks>
+    public interface IAccessorArray<T> : IReadOnlyList<T>  , IList<T>
+    {
+        // Because this.Count and this[index] exist at both at IList<T> and IReadOnlyList<T>,
+        // attempting to use them may cause an ambiguity error. This will be fixed in Net10.        
+        // see:
+        // https://github.com/dotnet/runtime/issues/31001#issuecomment-2942678308
+        // https://github.com/dotnet/runtime/pull/115802
+
+        new T this[int index] { get; set; }
+        new int Count { get; }                
+    }
+
+    public readonly struct ZeroAccessorArray<T> : IAccessorArray<T>
+    {
+        static ZeroAccessorArray()
+        {
+            _Default = default(T);
+            if (typeof(T) == typeof(float[])) _Default = (T)(Object)Array.Empty<T>();
+        }
+
+        public ZeroAccessorArray(int count)
+        {
+            Count = count;            
+        }
+
+        private static readonly T _Default;
+
+        public bool IsReadOnly => true;
+
+        public T this[int index] { get => _Default; set => throw new NotSupportedException(); }
+
+        public int Count { get; }
+
+        public int IndexOf(T item)
+        {
+            return Count > 0 && item.Equals(_Default) ? 0 : -1;
+        }
+
+        public bool Contains(T item)
+        {
+            return Count > 0 && item.Equals(_Default);
+        }
+
+        public void CopyTo(T[] array, int arrayIndex)
+        {
+            for(int i=0; i < Count; ++i)
+            {
+                array[i + arrayIndex] = default;
+            }
+        }        
+
+        public IEnumerator<T> GetEnumerator()
+        {
+            return Enumerable.Repeat(_Default, Count).GetEnumerator();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return Enumerable.Repeat(_Default, Count).GetEnumerator();
+        }
+
+        void IList<T>.Insert(int index, T item) { throw new NotSupportedException(); }
+
+        void IList<T>.RemoveAt(int index) { throw new NotSupportedException(); }
+
+        void ICollection<T>.Add(T item) { throw new NotSupportedException(); }
+
+        void ICollection<T>.Clear() { throw new NotSupportedException(); }
+
+        bool ICollection<T>.Remove(T item) { throw new NotSupportedException(); }
+    }
+}