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

tests/MrGameEng.Graphics.Tests/CameraMathTests.cs

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+using Microsoft.Xna.Framework;
+using MrGameEng.Graphics;
+using Xunit;
+
+namespace MrGameEng.Graphics.Tests;
+
+public class CameraMathTests
+{
+    private static void AssertVector(Vector2 expected, Vector2 actual, float tolerance = 0.001f)
+    {
+        Assert.InRange(actual.X, expected.X - tolerance, expected.X + tolerance);
+        Assert.InRange(actual.Y, expected.Y - tolerance, expected.Y + tolerance);
+    }
+
+    [Fact]
+    public void CameraPosition_MapsToScreenCenter()
+    {
+        var camera = new Camera(new Vector2(500f, 300f), zoom: 2f, rotation: 0.7f);
+
+        var state = CameraMath.Compute(camera, 800, 600, ViewportMapping.Identity);
+
+        AssertVector(new Vector2(400f, 300f), state.WorldToScreen(camera.Position));
+    }
+
+    [Fact]
+    public void ScreenToWorld_RoundTripsWithWorldToScreen()
+    {
+        var camera = new Camera(new Vector2(123f, -45f), zoom: 1.5f, rotation: 0.3f);
+        var state = CameraMath.Compute(camera, 1280, 720, new ViewportMapping(new Vector2(0f, 60f), 1.5f));
+
+        var screen = new Vector2(200f, 500f);
+        var world = state.ScreenToWorld(screen);
+
+        AssertVector(screen, state.WorldToScreen(world));
+    }
+
+    [Fact]
+    public void Zoom_ShrinksCullRect()
+    {
+        var camera = new Camera(Vector2.Zero, zoom: 2f);
+
+        var state = CameraMath.Compute(camera, 800, 600, ViewportMapping.Identity);
+
+        Assert.Equal(400f, state.CullRect.Width, 1);
+        Assert.Equal(300f, state.CullRect.Height, 1);
+        AssertVector(Vector2.Zero, state.CullRect.Center);
+    }
+
+    [Fact]
+    public void Rotation_ExpandsCullRectToCoverRotatedView()
+    {
+        var straight = CameraMath.Compute(new Camera(Vector2.Zero), 800, 600, ViewportMapping.Identity);
+        var rotated = CameraMath.Compute(new Camera(Vector2.Zero, rotation: MathF.PI / 4f), 800, 600, ViewportMapping.Identity);
+
+        Assert.True(rotated.CullRect.Width > straight.CullRect.Width);
+        Assert.True(rotated.CullRect.Height > straight.CullRect.Height);
+    }
+
+    [Fact]
+    public void Bounds_ClampCameraToWorldEdges()
+    {
+        var bounds = new RectF(0f, 0f, 2000f, 1000f);
+        var camera = new Camera(new Vector2(-500f, 500f), bounds: bounds);
+
+        var state = CameraMath.Compute(camera, 800, 600, ViewportMapping.Identity);
+
+        // Camera should be clamped so the view's left edge sits at the world's left edge.
+        AssertVector(new Vector2(0f, 200f), state.ScreenToWorld(Vector2.Zero));
+    }
+
+    [Fact]
+    public void Mapping_CentersVirtualResolutionInWiderWindow()
+    {
+        var mapping = CameraMath.ComputeMapping(1920, 1080, 640, 360);
+
+        Assert.Equal(3f, mapping.Scale);
+        Assert.Equal(Vector2.Zero, mapping.Offset);
+
+        var letterboxed = CameraMath.ComputeMapping(1920, 1200, 640, 360);
+        Assert.Equal(3f, letterboxed.Scale);
+        Assert.Equal(new Vector2(0f, 60f), letterboxed.Offset);
+    }
+}