Update README.md to include project description, developer documentation links, and license information.

src/MrGameEng.Graphics/SpriteBatcher.cs

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+using Microsoft.Xna.Framework;
+
+namespace MrGameEng.Graphics;
+
+/// <summary>One sprite queued for rendering this frame.</summary>
+public struct SpriteInstance
+{
+    /// <summary>Texture region to draw. Never null for submitted instances.</summary>
+    public Texture2DRegion Region;
+
+    /// <summary>World-space (or screen-space) center of the quad.</summary>
+    public Vector2 Center;
+
+    /// <summary>Half extents after scaling, in pixels. May be negative for negative scale.</summary>
+    public Vector2 HalfSize;
+
+    /// <summary>Rotation in radians, clockwise.</summary>
+    public float Rotation;
+
+    /// <summary>Tint color.</summary>
+    public Color Color;
+
+    /// <summary>Mirroring flags.</summary>
+    public SpriteFlip Flip;
+
+    /// <summary>Render layer the instance belongs to.</summary>
+    public byte Layer;
+}
+
+/// <summary>
+/// CPU side of the renderer: collects <see cref="SpriteInstance"/>s with their sort keys
+/// and orders them layer → depth → texture. Allocation-free after warm-up
+/// (arrays grow geometrically and are reused across frames).
+/// </summary>
+public sealed class SpriteBatcher
+{
+    private SpriteInstance[] _instances;
+    private ulong[] _keys;
+    private int[] _order;
+    private int _count;
+
+    /// <summary>Creates a batcher with the given initial capacity.</summary>
+    public SpriteBatcher(int initialCapacity = 2048)
+    {
+        _instances = new SpriteInstance[initialCapacity];
+        _keys = new ulong[initialCapacity];
+        _order = new int[initialCapacity];
+    }
+
+    /// <summary>Number of sprites submitted this frame.</summary>
+    public int Count => _count;
+
+    /// <summary>Queues one sprite.</summary>
+    public void Submit(in SpriteInstance instance, ulong sortKey)
+    {
+        if (_count == _instances.Length)
+        {
+            Grow();
+        }
+
+        _instances[_count] = instance;
+        _keys[_count] = sortKey;
+        _count++;
+    }
+
+    /// <summary>
+    /// Sorts all submitted sprites and returns their indices in draw order.
+    /// Valid until the next <see cref="Clear"/>.
+    /// </summary>
+    public ReadOnlySpan<int> Sort()
+    {
+        for (var i = 0; i < _count; i++)
+        {
+            _order[i] = i;
+        }
+
+        Array.Sort(_keys, _order, 0, _count);
+        return _order.AsSpan(0, _count);
+    }
+
+    /// <summary>Returns the instance at <paramref name="index"/> (an index from <see cref="Sort"/>).</summary>
+    public ref readonly SpriteInstance this[int index] => ref _instances[index];
+
+    /// <summary>Resets the batcher for the next frame. Keeps allocated capacity.</summary>
+    public void Clear() => _count = 0;
+
+    private void Grow()
+    {
+        var capacity = _instances.Length * 2;
+        Array.Resize(ref _instances, capacity);
+        Array.Resize(ref _keys, capacity);
+        Array.Resize(ref _order, capacity);
+    }
+}