From d7ecf019cbe66409d2e035f92ac4241f0c24ac8b Mon Sep 17 00:00:00 2001
From: MDietermann <marvin.dietermann@hive-brain.de>
Date: Thu, 28 May 2026 12:04:30 +0200
Subject: [PATCH] feat: add fly-camera with view/projection matrices

---
 Rendering/Camera.cs              | 54 ++++++++++++++++++++++++++++++++
 VoxelEngine.Tests/CameraTests.cs | 43 +++++++++++++++++++++++++
 2 files changed, 97 insertions(+)
 create mode 100644 Rendering/Camera.cs
 create mode 100644 VoxelEngine.Tests/CameraTests.cs

diff --git a/Rendering/Camera.cs b/Rendering/Camera.cs
new file mode 100644
index 0000000..357a415
--- /dev/null
+++ b/Rendering/Camera.cs
@@ -0,0 +1,54 @@
+using OpenTK.Mathematics;
+
+namespace VoxelEngine.Rendering;
+
+public sealed class Camera
+{
+    private static readonly Vector3 WorldUp = Vector3.UnitY;
+
+    public Vector3 Position { get; private set; }
+    public float Yaw { get; private set; } = -90f;   // degrees; -90 looks down -Z
+    public float Pitch { get; private set; } = 0f;    // degrees
+    public float Fov { get; set; } = 60f;             // degrees
+    public float AspectRatio { get; set; }
+
+    public Vector3 Front { get; private set; } = -Vector3.UnitZ;
+    public Vector3 Right { get; private set; } = Vector3.UnitX;
+    public Vector3 Up { get; private set; } = Vector3.UnitY;
+
+    public Camera(Vector3 position, float aspectRatio)
+    {
+        Position = position;
+        AspectRatio = aspectRatio;
+        UpdateVectors();
+    }
+
+    public void Move(Vector3 delta) => Position += delta;
+
+    public void AddRotation(float yawDelta, float pitchDelta)
+    {
+        Yaw += yawDelta;
+        Pitch = MathHelper.Clamp(Pitch + pitchDelta, -89f, 89f);
+        UpdateVectors();
+    }
+
+    public Matrix4 GetViewMatrix() => Matrix4.LookAt(Position, Position + Front, Up);
+
+    public Matrix4 GetProjectionMatrix() =>
+        Matrix4.CreatePerspectiveFieldOfView(
+            MathHelper.DegreesToRadians(Fov), AspectRatio, 0.1f, 100f);
+
+    private void UpdateVectors()
+    {
+        float yaw = MathHelper.DegreesToRadians(Yaw);
+        float pitch = MathHelper.DegreesToRadians(Pitch);
+
+        Front = Vector3.Normalize(new Vector3(
+            MathF.Cos(yaw) * MathF.Cos(pitch),
+            MathF.Sin(pitch),
+            MathF.Sin(yaw) * MathF.Cos(pitch)));
+
+        Right = Vector3.Normalize(Vector3.Cross(Front, WorldUp));
+        Up = Vector3.Normalize(Vector3.Cross(Right, Front));
+    }
+}
diff --git a/VoxelEngine.Tests/CameraTests.cs b/VoxelEngine.Tests/CameraTests.cs
new file mode 100644
index 0000000..0ac5a96
--- /dev/null
+++ b/VoxelEngine.Tests/CameraTests.cs
@@ -0,0 +1,43 @@
+using OpenTK.Mathematics;
+using VoxelEngine.Rendering;
+using Xunit;
+
+namespace VoxelEngine.Tests;
+
+public class CameraTests
+{
+    [Fact]
+    public void DefaultFront_PointsTowardNegativeZ()
+    {
+        var camera = new Camera(Vector3.Zero, 16f / 9f);
+
+        Assert.Equal(0f, camera.Front.X, 3);
+        Assert.Equal(0f, camera.Front.Y, 3);
+        Assert.Equal(-1f, camera.Front.Z, 3);
+    }
+
+    [Fact]
+    public void Move_TranslatesPosition()
+    {
+        var camera = new Camera(Vector3.Zero, 1f);
+        camera.Move(new Vector3(1f, 2f, 3f));
+        Assert.Equal(new Vector3(1f, 2f, 3f), camera.Position);
+    }
+
+    [Fact]
+    public void AddRotation_ClampsPitchTo89Degrees()
+    {
+        var camera = new Camera(Vector3.Zero, 1f);
+        camera.AddRotation(0f, 200f); // try to over-rotate up
+        Assert.True(camera.Pitch <= 89.0001f);
+        camera.AddRotation(0f, -400f);
+        Assert.True(camera.Pitch >= -89.0001f);
+    }
+
+    [Fact]
+    public void ProjectionMatrix_IsNotIdentity()
+    {
+        var camera = new Camera(Vector3.Zero, 1.5f);
+        Assert.NotEqual(Matrix4.Identity, camera.GetProjectionMatrix());
+    }
+}