feat(render): Phase A8.F — ViewPolygon + CellView clip-region data model

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/AcDream.App/Rendering/PortalView.cs

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+// PortalView.cs
+//
+// Phase A8.F: GL-free 2D screen-space (NDC) clip-region data model.
+// Mirrors retail view_poly (acclient.h:32465) and view_type (acclient.h:32338):
+// a cell's clip region is a SET of convex polygons in normalized device coords.
+using System.Collections.Generic;
+using System.Numerics;
+
+namespace AcDream.App.Rendering;
+
+/// <summary>One convex polygon in NDC screen space (xy in [-1,1]), plus its bounding rect.</summary>
+public readonly struct ViewPolygon
+{
+    public readonly Vector2[] Vertices;
+    public readonly float MinX, MinY, MaxX, MaxY;
+
+    public ViewPolygon(Vector2[] vertices)
+    {
+        Vertices = vertices;
+        if (vertices is null || vertices.Length < 3)
+        {
+            MinX = MinY = MaxX = MaxY = 0f;
+            return;
+        }
+        float minX = float.MaxValue, minY = float.MaxValue, maxX = float.MinValue, maxY = float.MinValue;
+        foreach (var v in vertices)
+        {
+            if (v.X < minX) minX = v.X;
+            if (v.X > maxX) maxX = v.X;
+            if (v.Y < minY) minY = v.Y;
+            if (v.Y > maxY) maxY = v.Y;
+        }
+        MinX = minX; MinY = minY; MaxX = maxX; MaxY = maxY;
+    }
+
+    public bool IsEmpty => Vertices is null || Vertices.Length < 3;
+}
+
+/// <summary>A cell's accumulated clip region: a set of convex view polygons + the union bounding rect.</summary>
+public sealed class CellView
+{
+    public readonly List<ViewPolygon> Polygons = new();
+    public float MinX { get; private set; } = float.MaxValue;
+    public float MinY { get; private set; } = float.MaxValue;
+    public float MaxX { get; private set; } = float.MinValue;
+    public float MaxY { get; private set; } = float.MinValue;
+
+    public bool IsEmpty => Polygons.Count == 0;
+
+    /// <summary>A region covering the entire NDC viewport — the camera cell's seed region
+    /// (mirrors retail PView::DrawInside copy_view(..., 4) at decomp:433814).</summary>
+    public static CellView FullScreen()
+    {
+        var v = new CellView();
+        v.Add(new ViewPolygon(new[]
+        {
+            new Vector2(-1f, -1f), new Vector2(1f, -1f), new Vector2(1f, 1f), new Vector2(-1f, 1f),
+        }));
+        return v;
+    }
+
+    public void Add(ViewPolygon p)
+    {
+        if (p.IsEmpty) return;
+        Polygons.Add(p);
+        if (p.MinX < MinX) MinX = p.MinX;
+        if (p.MinY < MinY) MinY = p.MinY;
+        if (p.MaxX > MaxX) MaxX = p.MaxX;
+        if (p.MaxY > MaxY) MaxY = p.MaxY;
+    }
+}

tests/AcDream.App.Tests/Rendering/PortalViewTests.cs

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+using System.Numerics;
+using AcDream.App.Rendering;
+using Xunit;
+
+namespace AcDream.App.Tests.Rendering;
+
+public class PortalViewTests
+{
+    [Fact]
+    public void ViewPolygon_ComputesBoundingRect()
+    {
+        var p = new ViewPolygon(new[]
+        {
+            new Vector2(-0.5f, -0.25f), new Vector2(0.5f, -0.25f), new Vector2(0.0f, 0.75f),
+        });
+        Assert.Equal(-0.5f, p.MinX, 5);
+        Assert.Equal(0.5f, p.MaxX, 5);
+        Assert.Equal(-0.25f, p.MinY, 5);
+        Assert.Equal(0.75f, p.MaxY, 5);
+        Assert.False(p.IsEmpty);
+    }
+
+    [Fact]
+    public void ViewPolygon_FewerThanThreeVerts_IsEmpty()
+    {
+        Assert.True(new ViewPolygon(new[] { new Vector2(0, 0), new Vector2(1, 0) }).IsEmpty);
+        Assert.True(new ViewPolygon(System.Array.Empty<Vector2>()).IsEmpty);
+    }
+
+    [Fact]
+    public void CellView_FullScreen_CoversNdc()
+    {
+        var v = CellView.FullScreen();
+        Assert.False(v.IsEmpty);
+        Assert.Equal(-1f, v.MinX, 5);
+        Assert.Equal(1f, v.MaxX, 5);
+        Assert.Equal(-1f, v.MinY, 5);
+        Assert.Equal(1f, v.MaxY, 5);
+    }
+
+    [Fact]
+    public void CellView_Add_GrowsUnionBoundsAndIsEmptyTracks()
+    {
+        var v = new CellView();
+        Assert.True(v.IsEmpty);
+        v.Add(new ViewPolygon(new[] { new Vector2(0, 0), new Vector2(0.2f, 0), new Vector2(0, 0.2f) }));
+        v.Add(new ViewPolygon(new[] { new Vector2(-0.3f, -0.3f), new Vector2(-0.1f, -0.3f), new Vector2(-0.1f, -0.1f) }));
+        Assert.False(v.IsEmpty);
+        Assert.Equal(-0.3f, v.MinX, 5);
+        Assert.Equal(0.2f, v.MaxX, 5);
+    }
+}