acdream/src/AcDream.App/Rendering/TeleportViewPlaneController.cs

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. At the exit edge retail swaps directly
/// from portal space to the destination world at the transition projection;
/// there is no black-alpha compositor between them.
/// </summary>
public sealed class TeleportViewPlaneController
{
    public const float TransitionViewPlaneDistance = 0.001f;

    private float _gameViewPlaneDistance = 1f;
    private readonly ProjectionOverrideCamera _projectionCamera = new();

    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 retail's view-plane state machine. Here "fade" is retail's state
    /// name for a projection transition: normal to 0.001 on fade-out, and
    /// 0.001 back to normal on fade-in. A logout transition retains the
    /// captured override during stable Tunnel; <c>EndTeleportAnimation</c>
    /// (<c>0x004D65D5</c>) releases it when entering TunnelContinue.
    /// </summary>
    public void Update(TeleportAnimSnapshot snapshot)
    {
        switch (snapshot.State)
        {
            case TeleportAnimState.WorldFadeOut:
            case TeleportAnimState.TunnelFadeIn:
            case TeleportAnimState.TunnelFadeOut:
            case TeleportAnimState.WorldFadeIn:
                Enabled = true;
                CurrentViewPlaneDistance = Lerp(
                    _gameViewPlaneDistance,
                    TransitionViewPlaneDistance,
                    snapshot.ViewPlaneBlend);
                break;

            case TeleportAnimState.Tunnel:
                // Retail preserves the captured FOV override through the
                // logout path's stable tunnel. A normal portal begins in
                // Tunnel with no override, so its disabled state is retained.
                if (Enabled)
                    CurrentViewPlaneDistance = _gameViewPlaneDistance;
                break;

            case TeleportAnimState.TunnelContinue:
            case TeleportAnimState.Off:
            default:
                Enabled = false;
                CurrentViewPlaneDistance = _gameViewPlaneDistance;
                break;
        }
    }

    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);
    }

    /// <summary>
    /// Decorate the active camera with the same projection returned by
    /// <see cref="Apply(Matrix4x4)"/>. Retail's <c>Render::set_vdst</c> is
    /// global to every 3-D draw; callers must pass this returned camera to
    /// terrain, meshes, particles, sky, weather, and portal-cell rendering so
    /// rasterization and frustum culling cannot use different projections.
    /// </summary>
    public ICamera ApplyTo(ICamera baseCamera)
    {
        ArgumentNullException.ThrowIfNull(baseCamera);
        _projectionCamera.Update(baseCamera, Apply(baseCamera.Projection));
        return _projectionCamera;
    }

    private static float Lerp(float from, float to, float amount) =>
        from + (to - from) * Math.Clamp(amount, 0f, 1f);

    private sealed class ProjectionOverrideCamera : ICamera
    {
        private ICamera _source = null!;

        public Matrix4x4 View => _source.View;
        public Matrix4x4 Projection { get; private set; } = Matrix4x4.Identity;
        public float Aspect
        {
            get => _source.Aspect;
            set => _source.Aspect = value;
        }

        public void Update(ICamera source, Matrix4x4 projection)
        {
            _source = source;
            Projection = projection;
        }
    }
}