fix(world): match retail portal passage and exit warp

src/AcDream.App/Rendering/TeleportViewPlaneController.cs

@@ -0,0 +1,98 @@
+using System.Numerics;
+using AcDream.Core.World;
+
+namespace AcDream.App.Rendering;
+
+/// <summary>
+/// Ports retail's teleport projection transition. <c>gmSmartBoxUI::UseTime</c>
+/// (<c>0x004D6E30</c>) eases SmartBox's view-plane distance between the
+/// active game's value and <c>TRANSITION_VIEW_PLANE_DISTANCE = 0.001</c>.
+/// <c>Render::set_vdst</c> (<c>0x0054B240</c>) converts that distance back to
+/// FOV and adjusts the near plane. This is the wide projection warp visible
+/// while the destination world emerges from black.
+/// </summary>
+public sealed class TeleportViewPlaneController
+{
+    public const float TransitionViewPlaneDistance = 0.001f;
+
+    private float _gameViewPlaneDistance = 1f;
+
+    public bool Enabled { get; private set; }
+    public float CurrentViewPlaneDistance { get; private set; } = 1f;
+
+    /// <summary>
+    /// Retail <c>BeginTeleportAnimation</c> captures
+    /// <c>SmartBox::GetOverrideFovDistance</c> once when starting from Off.
+    /// For a standard perspective matrix, M22 is exactly
+    /// <c>cot(verticalFov / 2)</c>, retail's view-plane-distance value.
+    /// </summary>
+    public void Begin(Matrix4x4 gameProjection)
+    {
+        float distance = gameProjection.M22;
+        if (!float.IsFinite(distance) || distance <= 0f)
+            distance = 1f;
+
+        _gameViewPlaneDistance = distance;
+        CurrentViewPlaneDistance = distance;
+        Enabled = false;
+    }
+
+    /// <summary>
+    /// Apply the four retail fade-state branches. Their projection blend is
+    /// numerically the same table-driven level as the black fade: normal to
+    /// 0.001 on fade-out, and 0.001 back to normal on fade-in.
+    /// </summary>
+    public void Update(TeleportAnimSnapshot snapshot)
+    {
+        Enabled = snapshot.State is TeleportAnimState.WorldFadeOut
+            or TeleportAnimState.TunnelFadeIn
+            or TeleportAnimState.TunnelFadeOut
+            or TeleportAnimState.WorldFadeIn;
+
+        CurrentViewPlaneDistance = Enabled
+            ? Lerp(_gameViewPlaneDistance, TransitionViewPlaneDistance, snapshot.FadeAlpha)
+            : _gameViewPlaneDistance;
+    }
+
+    public void Reset()
+    {
+        Enabled = false;
+        CurrentViewPlaneDistance = _gameViewPlaneDistance;
+    }
+
+    /// <summary>
+    /// Rebuild a perspective projection with retail's active view-plane
+    /// distance while preserving the source projection's aspect and far
+    /// plane. <c>Render::set_vdst</c> uses
+    /// <c>FOV = 2 * atan(1 / distance)</c> and
+    /// <c>znear = max(0.1, distance * 0.25)</c>.
+    /// </summary>
+    public Matrix4x4 Apply(Matrix4x4 baseProjection)
+    {
+        if (!Enabled)
+            return baseProjection;
+
+        float aspect = baseProjection.M11 != 0f
+            ? baseProjection.M22 / baseProjection.M11
+            : 1f;
+        float far = baseProjection.M33 != -1f
+            ? baseProjection.M43 / (baseProjection.M33 + 1f)
+            : 5000f;
+
+        if (!float.IsFinite(aspect) || aspect <= 0f)
+            aspect = 1f;
+        if (!float.IsFinite(far) || far <= 0.1f)
+            far = 5000f;
+
+        float distance = MathF.Max(CurrentViewPlaneDistance, TransitionViewPlaneDistance);
+        float fov = 2f * MathF.Atan(1f / distance);
+        float near = MathF.Max(0.1f, distance * 0.25f);
+        if (near >= far)
+            near = MathF.Min(0.1f, far * 0.5f);
+
+        return Matrix4x4.CreatePerspectiveFieldOfView(fov, aspect, near, far);
+    }
+
+    private static float Lerp(float from, float to, float amount) =>
+        from + (to - from) * Math.Clamp(amount, 0f, 1f);
+}