acdream/tests/AcDream.Core.Tests/Rendering/Wb/MeshExtractionConformanceTests.cs

using System.Numerics;
using AcDream.Core.Meshing;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Enums;
using DatReaderWriter.Lib;
using DatReaderWriter.Types;

namespace AcDream.Core.Tests.Rendering.Wb;

/// <summary>
/// Conformance: our <see cref="GfxObjMesh.Build"/> must produce the same
/// vertex-array + index-array output as WB's <c>ObjectMeshManager</c>
/// would for the same input GfxObj. We don't invoke WB's full pipeline
/// (it requires a GL context); instead we re-implement the WB algorithm
/// inline against the same source code we ported from, then compare.
///
/// <para>
/// If this test fails, either our port has drifted or the WB code has
/// changed upstream — investigate which, do not "fix" the test.
/// </para>
///
/// <para>
/// ONE DOCUMENTED EXCEPTION (#426, 2026-08-23):
/// <see cref="Build_NoPosFlag_EmitsBothPosAndNegSide"/> below intentionally
/// diverges from WorldBuilder's own upstream
/// <c>ObjectMeshManager.cs:959</c> (<c>if
/// (!poly.Stippling.HasFlag(StipplingType.NoPos))</c>), which has the exact
/// same bug our port faithfully carried over: gating the polygon's positive
/// side on <c>!NoPos</c>, silently dropping every solid-colour polygon.
/// Named-retail decomp (<c>D3DPolyRender::DrawMesh</c> @0x0059d4a0) proves
/// <c>NoPos</c> ("this side has no texture coordinates",
/// acclient.h:7380-7388) does not gate whether retail draws the positive
/// side at all — see #426 in docs/ISSUES.md for the full citation. This is
/// the one case in this file where the retail decomp — not WB — is the
/// oracle; see the acdream-wide rule in CLAUDE.md ("the decompiled code is
/// ground truth ... if they disagree, the decompiled code wins").
/// </para>
/// </summary>
public sealed class MeshExtractionConformanceTests
{
    [Fact]
    public void Build_QuadGfxObj_ProducesExpectedVerticesAndIndices()
    {
        var gfxObj = MakeUnitQuadGfxObj();

        var ours = GfxObjMesh.Build(gfxObj, dats: null);

        Assert.Single(ours);
        var sub = ours[0];
        // Quad → 4 vertices, 6 indices (two triangles via fan triangulation).
        Assert.Equal(4, sub.Vertices.Length);
        Assert.Equal(6, sub.Indices.Length);
        // Fan from vertex 0: (0,1,2) and (0,2,3).
        Assert.Equal(new uint[] { 0, 1, 2, 0, 2, 3 }, sub.Indices);
    }

    [Fact]
    public void Build_DoubleSidedPoly_ProducesBothPosAndNegSubmeshes()
    {
        var gfxObj = MakeUnitQuadGfxObj();
        var poly = gfxObj.Polygons[0];
        poly.Stippling = StipplingType.Both;
        // NegSurface=0 so the neg side references a valid surface entry.
        poly.NegSurface = 0;

        var ours = GfxObjMesh.Build(gfxObj, dats: null);

        Assert.Equal(2, ours.Count);
    }

    [Fact]
    public void Build_NoNegFlag_WithClockwiseSidesType_StillEmitsNegSide()
    {
        var gfxObj = MakeUnitQuadGfxObj();
        var poly = gfxObj.Polygons[0];
        poly.Stippling = StipplingType.None;
        poly.SidesType = CullMode.Clockwise;
        // NegSurface=0 so the neg side references a valid surface entry.
        poly.NegSurface = 0;

        var ours = GfxObjMesh.Build(gfxObj, dats: null);

        Assert.Equal(2, ours.Count);
    }

    /// <summary>
    /// #426 (2026-08-23): renamed from <c>Build_NoPosFlag_OnlyEmitsNegSide</c>,
    /// which asserted <c>Assert.Single(ours)</c> — the OLD bug's own
    /// behavior (NoPos silently dropped the positive side). NoPos means "no
    /// positive UVs" (acclient.h:7386), not "no positive face"; retail draws
    /// an ordinary object's untextured positive side same as a textured one
    /// (D3DPolyRender::DrawMesh @0x0059d4a0). See the class doc's "ONE
    /// DOCUMENTED EXCEPTION" note for why this test intentionally diverges
    /// from WorldBuilder's own (equally buggy) upstream algorithm.
    /// </summary>
    [Fact]
    public void Build_NoPosFlag_EmitsBothPosAndNegSide()
    {
        var gfxObj = MakeUnitQuadGfxObj();
        var poly = gfxObj.Polygons[0];
        poly.Stippling = StipplingType.NoPos | StipplingType.Negative;
        // NegSurface=0 so the neg side references a valid surface entry.
        poly.NegSurface = 0;

        var ours = GfxObjMesh.Build(gfxObj, dats: null);

        Assert.Equal(2, ours.Count);
    }

    /// <summary>
    /// Build a synthetic 1×1 quad GfxObj with vertex sequence [0,1,2,3]
    /// at corners (0,0,0)/(1,0,0)/(1,1,0)/(0,1,0). PosSurface=0,
    /// NegSurface=-1 (invalid — pos side only by default).
    /// No Stippling flags set by default — caller may add them per test.
    /// </summary>
    private static GfxObj MakeUnitQuadGfxObj()
    {
        var gfx = new GfxObj { Surfaces = { 0x08000000u } };
        gfx.VertexArray = new VertexArray
        {
            VertexType = VertexType.CSWVertexType,
            Vertices =
            {
                [0] = new SWVertex
                {
                    Origin = new Vector3(0, 0, 0),
                    Normal = new Vector3(0, 0, 1),
                    UVs = { new Vec2Duv { U = 0, V = 0 } },
                },
                [1] = new SWVertex
                {
                    Origin = new Vector3(1, 0, 0),
                    Normal = new Vector3(0, 0, 1),
                    UVs = { new Vec2Duv { U = 1, V = 0 } },
                },
                [2] = new SWVertex
                {
                    Origin = new Vector3(1, 1, 0),
                    Normal = new Vector3(0, 0, 1),
                    UVs = { new Vec2Duv { U = 1, V = 1 } },
                },
                [3] = new SWVertex
                {
                    Origin = new Vector3(0, 1, 0),
                    Normal = new Vector3(0, 0, 1),
                    UVs = { new Vec2Duv { U = 0, V = 1 } },
                },
            },
        };

        var poly = new Polygon
        {
            VertexIds = { 0, 1, 2, 3 },
            PosUVIndices = { 0, 0, 0, 0 },
            PosSurface = 0,
            NegSurface = -1,  // invalid index — pos side only
            Stippling = StipplingType.None,
            SidesType = CullMode.None,
        };
        gfx.Polygons[0] = poly;
        return gfx;
    }
}