refactor(content): share EnvCell geometry identity

tests/AcDream.Core.Tests/Rendering/Wb/EnvCellGeometryIdentityTests.cs

@@ -0,0 +1,42 @@
+using AcDream.Core.Rendering.Wb;
+
+namespace AcDream.Core.Tests.Rendering.Wb;
+
+public sealed class EnvCellGeometryIdentityTests
+{
+    [Fact]
+    public void Compute_EmptySurfaces_MatchesExtractedWorldBuilderValue()
+    {
+        Assert.Equal(
+            0x2_0000_47D6UL,
+            EnvCellGeometryIdentity.Compute(0x42, 7, Array.Empty<ushort>()));
+    }
+
+    [Fact]
+    public void Compute_OrderedSurfaces_MatchesExtractedWorldBuilderValue()
+    {
+        Assert.Equal(
+            0x2_20A7_A46CUL,
+            EnvCellGeometryIdentity.Compute(0x42, 7, new ushort[] { 1, 2, 3 }));
+    }
+
+    [Fact]
+    public void Compute_SurfaceOrderIsPartOfIdentity()
+    {
+        var forward = EnvCellGeometryIdentity.Compute(1, 1, new ushort[] { 10, 20 });
+        var reverse = EnvCellGeometryIdentity.Compute(1, 1, new ushort[] { 20, 10 });
+
+        Assert.NotEqual(forward, reverse);
+    }
+
+    [Fact]
+    public void Compute_AlwaysUsesDeduplicatedGeometryNamespace()
+    {
+        var id = EnvCellGeometryIdentity.Compute(
+            uint.MaxValue,
+            ushort.MaxValue,
+            new ushort[] { ushort.MaxValue, ushort.MaxValue });
+
+        Assert.NotEqual(0UL, id & 0x2_0000_0000UL);
+    }
+}