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

using System;
using System.Numerics;

namespace AcDream.App.Rendering;

/// <summary>
/// BR-2 (holistic building-render port): retail's invisible portal depth
/// writes — the port of <c>D3DPolyRender::DrawPortalPolyInternal</c>
/// (Ghidra 0x0059bc90, pc:424490).
///
/// <para><b>Wired by T1 (BR-3, `579c8b0`):</b> seal on interior roots, punch
/// on outdoor / look-in roots, via <c>RetailPViewPassExecutor.DrawPortalDepthWrite</c>
/// (the <c>DrawExitPortalMasks</c> slice callback) — safe alongside the
/// dynamics-drawn-LAST frame order (the first BR-2 attempt punched after
/// dynamics and erased the player; reverted 88be519). #117 (2026-06-11)
/// added the two-pass stencil depth gate on the punch side — see
/// <see cref="DrawDepthFan"/>.</para>
///
/// <para>Retail projects a portal polygon, software-clips it against the
/// installed portal view (<c>polyClipFinish</c>), and draws the survivor as a
/// COLOR-INVISIBLE triangle fan with depth-test ALWAYS + depth-write ON:</para>
/// <list type="bullet">
///   <item><b>Seal</b> (retail <c>maxZ2=6</c>, bit0 clear, data 0x00820e14):
///   z = the polygon's true projected depth. Drawn on portals leading OUTSIDE
///   (<c>other_cell_id==0xFFFF</c>) after the landscape pass — terrain seen
///   through a doorway keeps its pixels because farther interior geometry
///   z-fails inside the aperture (PView::DrawCells loop 1, Ghidra 0x005a4840,
///   pc:432783-432786).</item>
///   <item><b>Punch</b> (retail <c>maxZ1=7</c>, bit0 set, data 0x00820e18):
///   z forced to the far plane (0.99999988) — erases depth inside a building
///   aperture so the interior cells drawn next land cleanly
///   (ConstructView(CBldPortal) mode-1, pc:433827). BR-2 commit 2 wires this
///   side.</item>
/// </list>
///
/// <para>Where retail clips the polygon on the CPU against the view, we apply
/// the SAME view region via <c>gl_ClipDistance</c> from the slice's clip-space
/// half-planes (≤8, the validated <see cref="ClipPlaneSet"/> output) — the
/// depth write lands only inside the slice region, matching retail's clipped
/// fan.</para>
///
/// <para>The GL arm's inline program (rehomed clip planes, raw uniform
/// locations) and this class's own dynamic VAO/VBO ring were deleted at
/// Campaign V slice V11; the RHI arm compiles
/// <c>Rendering/Shaders/portal_depth.{vert,frag}</c> from committed SPIR-V,
/// and its per-frame fan vertices come from the frame ring instead.</para>
/// </summary>
public sealed partial class PortalDepthMaskRenderer : IDisposable
{
    private readonly ResourceCleanupGroup _resources;

    /// <summary>Shared by both arms: the largest fan <see cref="DrawDepthFan"/> accepts.</summary>
    private const int MaxFanVerts = 32;

    /// <summary>
    /// The GL arm's per-flight VAO/VBO ring this used to report on was deleted
    /// at Campaign V slice V11: the RHI arm draws every fan from a ring
    /// allocation that lives until its frame retires, so there is no
    /// persistent dynamic-buffer pool left to size.
    /// </summary>
    internal long DynamicBufferCapacityBytes => 0;

    /// <summary>
    /// Selects the GPU-fenced frame slot and resets its append cursor. Portal
    /// fans written during one frame occupy distinct ranges, so later portal
    /// slices never overwrite vertices still referenced by earlier draws.
    ///
    /// <para>The GL arm's per-flight VAO/VBO ring this used to activate was
    /// deleted at Campaign V slice V11 — the RHI arm owns no per-flight ring
    /// at all, because every frame ring allocation is already distinct memory
    /// that lives until the frame retires — so all this edge carries now is
    /// the started latch.</para>
    /// </summary>
    public void BeginFrame(int frameSlot)
    {
        ArgumentOutOfRangeException.ThrowIfNegative(frameSlot);
        _rhiFrameStarted = true;
    }

    /// <summary>
    /// #117 (2026-06-11): the mark-pass depth bias, in NDC, toward the
    /// viewer. Retail's punch is DEPTHTEST_ALWAYS and is safe only because
    /// retail's outdoor pass is painter's-ordered far→near (anything nearer
    /// redraws AFTER the punch and re-covers it). Our z-buffered MDI frame
    /// has no such order, so an unconditional far-Z punch erased the depth
    /// of NEARER occluders (terrain hills, closer buildings) at aperture
    /// pixels — doors/interiors painted through them (the T5 #117 report).
    /// The z-buffer-correct equivalent: punch ONLY where the aperture
    /// polygon itself wins a depth test at its true depth (two-pass
    /// stencil below). The bias keeps the #108 case covered — terrain
    /// hugging the door plane (centimeters in front of the aperture) must
    /// still be punched; a hill or another house meters nearer must not.
    /// </summary>
    private const float PunchMarkDepthBias = 0.0005f;

    /// <summary>
    /// #129 (2026-06-12): NDC depth is non-linear — a constant NDC bias b
    /// spans ≈ b·d²/near meters of eye depth at eye distance d. With
    /// znear = 0.1, the 0.0005 constant alone spanned 0.125 m at 5 m but
    /// ~190 m at a landblock away: every hill/house in front of a distant
    /// aperture passed the mark and got far-Z punched — door-shaped leaks
    /// through occluders. Fix: cap the bias's EYE-SPACE span at
    /// <see cref="PunchMarkBiasEyeCapMeters"/>. Below the ~10 m crossover
    /// (sqrt(cap·near/0.0005)) the constant-NDC term is smaller and wins —
    /// bit-identical to the T5-validated close-range behavior (#108 grass
    /// coverage untouched); beyond it the punch can never reach an occluder
    /// more than the cap in front of the aperture plane.
    /// </summary>
    public const float PunchMarkBiasEyeCapMeters = 0.5f;

    /// <summary>Retail <c>Render::znear</c> = 0.1 (decomp :342173, re-landed
    /// d4b5c71). The cap conversion below assumes the production camera near
    /// plane; the small f/(f−n) factor (~1.00002 at far 5000) is ignored.</summary>
    public const float CameraNearPlaneMeters = 0.1f;

    /// <summary>CPU mirror of the vertex-shader mark-bias expression (keep in
    /// sync with <c>VertSrc</c>): the NDC bias applied at eye depth
    /// <paramref name="eyeDepthMeters"/>.</summary>
    public static float MarkBiasNdc(float eyeDepthMeters) =>
        MathF.Min(PunchMarkDepthBias,
            PunchMarkBiasEyeCapMeters * CameraNearPlaneMeters
            / MathF.Max(eyeDepthMeters * eyeDepthMeters, 1e-6f));

    /// <summary>
    /// Draw one portal polygon as an invisible depth write, clipped to the
    /// slice's clip-space half-planes. <paramref name="forceFarZ"/> selects
    /// punch (true, retail maxZ1) vs seal (false, retail maxZ2 true depth).
    ///
    /// <para><b>Seal</b> (interior root): one pass, retail-verbatim —
    /// depth ALWAYS + true projected depth. It runs immediately after the
    /// gated full depth clear, so there is no nearer content to stomp.</para>
    ///
    /// <para><b>Punch</b> (outdoor root / look-in): two passes (#117).
    /// Pass A marks stencil where the aperture fan passes a LEQUAL depth
    /// test at its (biased) true depth — i.e. where the aperture is
    /// actually visible against everything drawn so far. Pass B writes the
    /// far-Z punch with depth ALWAYS but stencil-gated to the marked
    /// pixels, and zeroes the stencil as it goes (self-cleaning). This is
    /// the z-buffered equivalent of retail's painter's-order safety.</para>
    /// </summary>
    public void DrawDepthFan(
        ReadOnlySpan<Vector3> worldVerts,
        in Matrix4x4 viewProjection,
        ReadOnlySpan<Vector4> planes,
        bool forceFarZ)
    {
        if (worldVerts.Length < 3)
            return;
        DrawDepthFanRhi(worldVerts, in viewProjection, planes, forceFarZ);
    }

    public void Dispose() => DisposeRhiResources();
}