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

src/MrGameEng.Graphics/RenderSystems.cs

@@ -0,0 +1,66 @@
+using Friflo.Engine.ECS.Systems;
+
+namespace MrGameEng.Graphics;
+
+/// <summary>
+/// First draw system: finds the active camera entity (the first one with a <see cref="Camera"/>
+/// component) and begins the renderer frame. Without a camera entity a default camera showing
+/// world origin at the top-left corner is used.
+/// </summary>
+public sealed class CameraSystem : QuerySystem<Camera>
+{
+    private readonly Renderer2D _renderer;
+
+    /// <summary>Creates the system for <paramref name="renderer"/>.</summary>
+    public CameraSystem(Renderer2D renderer) => _renderer = renderer;
+
+    /// <inheritdoc />
+    protected override void OnUpdate()
+    {
+        foreach (var (cameras, _) in Query.Chunks)
+        {
+            if (cameras.Length > 0)
+            {
+                _renderer.BeginFrame(in cameras.Span[0]);
+                return;
+            }
+        }
+
+        _renderer.BeginFrameWithDefaultCamera();
+    }
+}
+
+/// <summary>Submits every entity that has both <see cref="Sprite"/> and <see cref="Transform2D"/>.</summary>
+public sealed class SpriteRenderSystem : QuerySystem<Sprite, Transform2D>
+{
+    private readonly Renderer2D _renderer;
+
+    /// <summary>Creates the system for <paramref name="renderer"/>.</summary>
+    public SpriteRenderSystem(Renderer2D renderer) => _renderer = renderer;
+
+    /// <inheritdoc />
+    protected override void OnUpdate()
+    {
+        foreach (var (sprites, transforms, _) in Query.Chunks)
+        {
+            var s = sprites.Span;
+            var t = transforms.Span;
+            for (var i = 0; i < s.Length; i++)
+            {
+                _renderer.Submit(in t[i], in s[i]);
+            }
+        }
+    }
+}
+
+/// <summary>Last draw system: sorts the frame and issues the draw calls.</summary>
+public sealed class RenderFlushSystem : BaseSystem
+{
+    private readonly Renderer2D _renderer;
+
+    /// <summary>Creates the system for <paramref name="renderer"/>.</summary>
+    public RenderFlushSystem(Renderer2D renderer) => _renderer = renderer;
+
+    /// <inheritdoc />
+    protected override void OnUpdateGroup() => _renderer.EndFrame();
+}