feat(D.2b): Slice 2 — DollCamera (fixed paperdoll ICamera)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/DollCamera.cs

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+using System.Numerics;
+
+namespace AcDream.App.Rendering;
+
+/// <summary>
+/// Fixed camera for the paperdoll mini-scene. Eye and look-at from
+/// <c>gmPaperDollUI::PostInit</c> (decomp lines 175521–175527):
+/// eye (0.12, -2.4, 0.88) looking at the origin, AC up-axis = +Z.
+///
+/// Uses the same <see cref="Matrix4x4.CreateLookAt"/> /
+/// <see cref="Matrix4x4.CreatePerspectiveFieldOfView"/> convention as
+/// <see cref="ChaseCamera"/> so the doll's triangle winding and back-face
+/// culling match the world render pass.
+///
+/// Per-race camera distance (<c>UpdateForRace</c>) is deferred polish.
+/// </summary>
+public sealed class DollCamera : ICamera
+{
+    private static readonly Vector3 Eye    = new(0.12f, -2.4f, 0.88f);
+    private static readonly Vector3 Target = Vector3.Zero;
+    private static readonly Vector3 Up     = Vector3.UnitZ;   // AC up-axis = +Z, same as ChaseCamera
+
+    /// <summary>Vertical field of view in radians. ~34° default; tune at the visual gate.</summary>
+    public float FovRadians { get; set; } = 0.6f;
+
+    public float Near   { get; set; } = 0.1f;    // same near plane as ChaseCamera / retail znear
+    public float Far    { get; set; } = 50f;      // doll scene is small; 50 m is ample
+    public float Aspect { get; set; } = 1f;
+
+    /// <inheritdoc/>
+    public Matrix4x4 View =>
+        Matrix4x4.CreateLookAt(Eye, Target, Up);
+
+    /// <inheritdoc/>
+    public Matrix4x4 Projection =>
+        Matrix4x4.CreatePerspectiveFieldOfView(FovRadians, Aspect <= 0f ? 1f : Aspect, Near, Far);
+}

tests/AcDream.App.Tests/Rendering/DollCameraTests.cs

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+using System.Numerics;
+using AcDream.App.Rendering;
+using Xunit;
+
+namespace AcDream.App.Tests.Rendering;
+
+public class DollCameraTests
+{
+    [Fact]
+    public void Eye_position_is_the_retail_camera_offset()
+    {
+        var cam = new DollCamera { Aspect = 100f / 214f };
+        Assert.True(Matrix4x4.Invert(cam.View, out var inv));
+        var eye = inv.Translation;
+        Assert.Equal(0.12f, eye.X, 3);
+        Assert.Equal(-2.4f, eye.Y, 3);
+        Assert.Equal(0.88f, eye.Z, 3);
+    }
+
+    [Fact]
+    public void Projection_is_finite_and_uses_aspect()
+    {
+        var cam = new DollCamera { Aspect = 1.5f };
+        Assert.True(float.IsFinite(cam.Projection.M11));
+        Assert.NotEqual(0f, cam.Projection.M34);   // perspective w = -z term
+    }
+}