acdream/tests/AcDream.App.Tests/Rendering/PortalProjectionTests.cs

using System;
using System.Numerics;
using AcDream.App.Rendering;
using Xunit;

namespace AcDream.App.Tests.Rendering;

public class PortalProjectionTests
{
    // A simple GL-style perspective looking down -Z, camera at origin.
    private static Matrix4x4 ViewProj()
    {
        var view = Matrix4x4.CreateLookAt(Vector3.Zero, new Vector3(0, 0, -1), Vector3.UnitY);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(1.0f, 1.0f, 0.1f, 1000f);
        return view * proj;
    }

    [Fact]
    public void Project_QuadInFront_ProducesNdcInsideViewport()
    {
        // A 2x2 quad at z=-5 (in front), cell-local == world (identity transform).
        var poly = new[]
        {
            new Vector3(-1, -1, -5), new Vector3(1, -1, -5), new Vector3(1, 1, -5), new Vector3(-1, 1, -5),
        };
        var r = PortalProjection.ProjectToNdc(poly, Matrix4x4.Identity, ViewProj());
        Assert.True(r.Length >= 3);
        foreach (var v in r)
        {
            Assert.InRange(v.X, -1.001f, 1.001f);
            Assert.InRange(v.Y, -1.001f, 1.001f);
        }
    }

    [Fact]
    public void Project_QuadFullyBehind_ReturnsEmpty()
    {
        var poly = new[]
        {
            new Vector3(-1, -1, 5), new Vector3(1, -1, 5), new Vector3(1, 1, 5), new Vector3(-1, 1, 5),
        };
        var r = PortalProjection.ProjectToNdc(poly, Matrix4x4.Identity, ViewProj());
        Assert.True(r.Length < 3);
    }

    [Fact]
    public void Project_QuadStraddlingCamera_ClipsWithoutInversion()
    {
        // Spans from behind (z=+2) to in front (z=-5). Must clip to the in-front part,
        // never produce a wildly out-of-range inverted vertex.
        var poly = new[]
        {
            new Vector3(-1, -1, 2), new Vector3(1, -1, -5), new Vector3(1, 1, -5), new Vector3(-1, 1, 2),
        };
        var r = PortalProjection.ProjectToNdc(poly, Matrix4x4.Identity, ViewProj());
        Assert.True(r.Length >= 3);
        foreach (var v in r)
        {
            // A corner a few cm in front of the eye and ~1 m to the side genuinely
            // projects large (~±37 NDC) but finite. ±50 still catches the ±7852
            // perspective-inversion blow-up the old w-clip produced.
            Assert.InRange(v.X, -50f, 50f); // bounded — no inversion blow-up
            Assert.InRange(v.Y, -50f, 50f);
        }
    }

    [Fact]
    public void Project_QuadStraddlingCamera_DownstreamIntersectionIsValidOnScreen()
    {
        var poly = new[]
        {
            new Vector3(-1, -1, 2), new Vector3(1, -1, -5), new Vector3(1, 1, -5), new Vector3(-1, 1, 2),
        };
        var projected = PortalProjection.ProjectToNdc(poly, Matrix4x4.Identity, ViewProj());
        Assert.True(projected.Length >= 3);

        // The viewport region (NDC [-1,1]^2), same as CellView.FullScreen()'s single polygon.
        var viewport = CellView.FullScreen().Polygons[0].Vertices;
        var onScreen = ScreenPolygonClip.Intersect(projected, viewport);

        Assert.True(onScreen.Length >= 3); // a non-empty visible region survives
        foreach (var v in onScreen)
        {
            Assert.InRange(v.X, -1.001f, 1.001f);
            Assert.InRange(v.Y, -1.001f, 1.001f);
        }
    }

    [Fact]
    public void Project_PortalEyeIsAlmostTouching_StaysVisibleOnScreen()
    {
        // Regression (2026-06-03 doorway "void"): the chase camera orbits to ~0.1 m from a
        // doorway portal. With RetailChaseCamera's 1.0 m near plane and the old w+z>=0 GL
        // near-clip — which, for a D3D CreatePerspectiveFieldOfView matrix, discards everything
        // within ~0.5 m of the eye — the whole doorway was clipped to empty, so the room behind
        // it was culled and rendered as a dark void (camera-orientation dependent; rotating away
        // fixed it). The eye-clip must be near-INDEPENDENT: a portal you're standing in must
        // still project (covering the screen) so the cell behind stays visible.
        var view = Matrix4x4.CreateLookAt(Vector3.Zero, new Vector3(0, 0, -1), Vector3.UnitY);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 3f, 16f / 9f, 1.0f, 5000f); // RetailChaseCamera
        var viewProj = view * proj;

        // A 2 m x 2 m doorway 0.1 m in front of the eye, facing it.
        var doorway = new[]
        {
            new Vector3(-1f, -1f, -0.1f), new Vector3(1f, -1f, -0.1f),
            new Vector3(1f,  1f, -0.1f),  new Vector3(-1f, 1f, -0.1f),
        };

        var projected = PortalProjection.ProjectToNdc(doorway, Matrix4x4.Identity, viewProj);
        Assert.True(projected.Length >= 3,
            "a doorway 0.1 m from the eye must still project (was clipped to empty -> void)");

        var viewport = CellView.FullScreen().Polygons[0].Vertices;
        var onScreen = ScreenPolygonClip.Intersect(projected, viewport);
        Assert.True(onScreen.Length >= 3,
            "the cell behind a doorway you're standing in must stay visible (the void bug)");
    }
}