using DatReaderWriter.Enums;

namespace AcDream.Core.Meshing;

/// <summary>
/// Retail's textured-vs-untextured surface classification, ported from
/// <c>D3DPolyRender::DrawMesh</c> @0x0059d4a0 (named-retail decomp,
/// docs/research/named-retail/acclient_2013_pseudo_c.txt ~line 426048): a
/// surface subset is TEXTURED — and therefore never subject to either of
/// retail's "skip untextured" gates (see
/// <see cref="RetailUntexturedSubsetPolicy"/>) — when
/// <c>(surface-&gt;type &amp; 6) != 0</c>, i.e. when
/// <see cref="SurfaceType.Base1Image"/> (<c>BASE1_IMAGE</c>, 0x2) or
/// <see cref="SurfaceType.Base1ClipMap"/> (<c>BASE1_CLIPMAP</c>, 0x4) is set
/// (docs/research/named-retail/acclient.h:5822-5824). Every other surface —
/// including <see cref="SurfaceType.Base1Solid"/> and any surface whose type
/// carries neither bit — is UNTEXTURED: a flat-colour ("solid") subset filled
/// from <c>Surface.ColorValue</c> rather than a decoded texture.
/// </summary>
/// <remarks>
/// #426 (2026-08-23, the Holtburg windmill axle 0x010010CE): the polygon-side
/// <c>StipplingType.NoPos</c> flag ("this side has no texture coordinates",
/// acclient.h:7386) is NOT the same fact as "this surface is untextured" —
/// every solid-colour polygon carries NoPos (it has no UVs to carry), but
/// NoPos says nothing about whether the surface itself is textured. The old
/// extraction conflated the two (<c>isSolid = NoPos || Base1Solid</c>) and,
/// worse, used NoPos to decide whether to emit the polygon's positive side AT
/// ALL — dropping every solid-colour polygon on every object. This type is
/// the ONE place that answers "is this surface textured", built from the
/// Surface's own Type flags so extraction (isSolid / TextureKey.IsSolid) and
/// draw-time skip policy agree by construction.
/// </remarks>
public static class RetailUntexturedSurfacePolicy
{
    public static bool IsUntextured(SurfaceType type) =>
        (type & (SurfaceType.Base1Image | SurfaceType.Base1ClipMap)) == 0;
}

/// <summary>
/// Retail's draw-time policy for an UNTEXTURED (solid-colour) mesh subset on
/// an ordinary <see cref="AcDream.Core.World.WorldEntity"/>, ported from the
/// same <c>D3DPolyRender::DrawMesh</c> untextured branch: the subset draws
/// unless <c>skipNoTexture != 0 &amp;&amp;
/// RenderDeviceD3D::ObjBuildingOrBuildingPart != 0</c>. <c>skipNoTexture</c>
/// @0x00820e30 is a global initialised to 1 and never cleared, so in
/// practice the gate reduces to
/// <c>RenderDeviceD3D::ObjBuildingOrBuildingPart == 0</c>.
/// <c>RenderDeviceD3D::DrawBuilding</c> (@0x0059f2a0) sets that flag around
/// the building-shell draw, so a building shell's own untextured subsets are
/// the ONE case where an ordinary WorldEntity skips them — statics, scenery,
/// creatures, and items (<c>DrawMeshInternal</c> @0x0059f360 →
/// <c>DrawMesh(gfxobj, mesh, arg4: 0)</c>) always draw their untextured
/// subsets.
/// </summary>
/// <remarks>
/// EnvCell interiors are retail's OTHER "skip untextured" case
/// (<c>RenderDeviceD3D::DrawEnvCell</c> @0x0059f170 calls
/// <c>DrawMesh(..., arg4: 1)</c>), but EnvCell/CellStruct geometry never
/// reaches this predicate — it draws through <c>EnvCellRenderer</c> /
/// <c>MeshExtractor.PrepareCellStructMeshData</c>, which keeps its own
/// NoPos-based approximation of the same rule (see
/// <c>docs/architecture/retail-divergence-register.md</c> AP-234 and
/// <c>CellMesh.cs</c>'s matching gate).
/// <para>
/// ONE shared predicate for <c>WbDrawDispatcher</c>'s classic classifier
/// (<c>ClassifyBatches</c>), packed classifier (<c>ClassifyPackedBatches</c>),
/// and the directional-shadow caster walk (<c>AddDirectionalShadowBatches</c>)
/// — Campaign VM VM6 showed that two hand-maintained classifiers computing
/// the "same" fact independently drift apart.
/// </para>
/// </remarks>
public static class RetailUntexturedSubsetPolicy
{
    public static bool Draws(bool isBuildingShell, bool isUntextured) =>
        !isUntextured || !isBuildingShell;
}