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

using System.Numerics;
using AcDream.Core.Physics;

namespace AcDream.App.Rendering;

/// <summary>
/// <see cref="ICameraCollisionProbe"/> backed by the player's swept-sphere
/// engine. Ports retail's <c>SmartBox::update_viewer</c> (0x00453ce0): sweep
/// the 0.3 m <c>viewer_sphere</c> from the head-pivot to the desired eye via a
/// <c>CTransition</c> and use the stopped position. Reusing
/// <see cref="PhysicsEngine.ResolveWithTransition"/> collides against indoor
/// cell walls (<c>FindEnvCollisions</c>) AND outdoor/baked GfxObj shells
/// (<c>FindObjCollisions</c>) in one faithful path.
/// </summary>
public sealed class PhysicsCameraCollisionProbe : ICameraCollisionProbe
{
    /// <summary>Retail <c>viewer_sphere</c> radius (acclient :93314).</summary>
    public const float ViewerSphereRadius = 0.3f;

    private readonly PhysicsEngine _physics;

    public PhysicsCameraCollisionProbe(PhysicsEngine physics) => _physics = physics;

    public Vector3 SweepEye(Vector3 pivot, Vector3 desiredEye, uint cellId, uint selfEntityId)
    {
        // No starting cell → nothing to sweep against; keep the desired eye.
        if (cellId == 0) return desiredEye;

        // SpherePath.InitPath puts sphere0's center at pathPos + (0,0,radius)
        // (the player foot-capsule convention). Retail's viewer_sphere center is
        // (0,0,0), so shift the path DOWN by the radius to make the SPHERE CENTER
        // travel pivot→eye, then add it back to the swept stop position.
        Vector3 begin = ToSpherePath(pivot,      ViewerSphereRadius);
        Vector3 end   = ToSpherePath(desiredEye, ViewerSphereRadius);

        var r = _physics.ResolveWithTransition(
            currentPos:     begin,
            targetPos:      end,
            cellId:         cellId,
            sphereRadius:   ViewerSphereRadius,
            sphereHeight:   0f,                    // single sphere (no head sphere)
            stepUpHeight:   0f,                    // no step-up for a camera
            stepDownHeight: 0f,                    // no step-down / ground snap
            isOnGround:     false,                 // no contact-plane / walkable semantics
            body:           null,                  // no cross-frame persistence
            // Retail SmartBox::update_viewer calls init_object(player, 0x5c) =
            // IsViewer | PathClipped | FreeRotate | PerfectClip (acclient
            // pseudo-C :92864; enum TransitionTypes.cs:24-33). PathClipped makes
            // the sweep HARD-STOP at first contact (TransitionTypes.cs:811) — the
            // spring-arm pull-in, not the player's edge-slide. IsViewer lets the
            // eye pass through creatures, colliding only with world geometry
            // (CollisionExemption.cs:83-85). FreeRotate/PerfectClip are no-ops in
            // acdream today but set to match retail's exact value. NOT IsPlayer
            // (0x100), so camera sweeps stay out of the #98 capture filter.
            moverFlags:     ObjectInfoState.IsViewer | ObjectInfoState.PathClipped
                          | ObjectInfoState.FreeRotate | ObjectInfoState.PerfectClip,
            movingEntityId: selfEntityId);         // skip the player's own ShadowEntry

        Vector3 eye = FromSpherePath(r.Position, ViewerSphereRadius);

        // Phase U.4c spike apparatus (THROWAWAY — strip with ACDREAM_PROBE_FLAP).
        // The post-fix [flap-cam] capture shows the eye flying to full chase distance
        // (eyeInRoot=n ~90%) in cells like 0xA9B40174/0175 — i.e. this sweep is not
        // stopping it. This line answers WHY, the fork that picks the primary residual
        // fix: pulledIn≈0 with resolved=Y bsp=ok ⇒ the sweep ran but found NOTHING in
        // that cell (space genuinely open, or wall geometry the per-cell sweep can't
        // reach → clip-robustness is primary); resolved=n / bsp=nobsp/noroot ⇒ collision
        // can't even run there (cell/BSP not loaded → camera-collision reliability is
        // primary); pulledIn large ⇒ collision IS engaging (eye leaving is then expected
        // through an opening). Paired per-frame with the builder's [flap]/[flap-cam].
        if (AcDream.Core.Rendering.RenderingDiagnostics.ProbeFlapEnabled)
        {
            var cp = _physics.DataCache?.GetCellStruct(cellId);
            string bsp = cp?.BSP is null ? "nobsp" : (cp.BSP.Root is null ? "noroot" : "ok");
            float desiredBack = Vector3.Distance(pivot, desiredEye);
            float eyeBack     = Vector3.Distance(pivot, eye);
            System.Console.WriteLine(
                $"[flap-sweep] cell=0x{cellId:X8} resolved={(cp is not null ? "Y" : "n")} bsp={bsp} " +
                $"desiredBack={desiredBack:F2} eyeBack={eyeBack:F2} pulledIn={desiredBack - eyeBack:F2} " +
                $"collNormValid={r.CollisionNormalValid}");
        }

        return eye;
    }

    /// <summary>Eye/pivot point → InitPath path point (subtract the sphere-center offset).</summary>
    internal static Vector3 ToSpherePath(Vector3 spherePoint, float radius)
        => spherePoint - new Vector3(0f, 0f, radius);

    /// <summary>InitPath path point → eye point (add the sphere-center offset back).</summary>
    internal static Vector3 FromSpherePath(Vector3 pathPoint, float radius)
        => pathPoint + new Vector3(0f, 0f, radius);
}