Gravity.cginc is generated: GravityShader.Source() is its one author, a test pins the committed file to it byte for byte

The mirror test compared a normalised reading of two spellings and was beaten twice (a statement before the return, gravityHeight's sum). GravityShader writes the whole file (potential, zero-strength guard, reference term, height sum) from GravityField's constant (TailOffset); GravityShaderTests fails on any difference. GravityShaderMirrorTests deleted. GravityFieldParityVerify opens Main Menu.unity: no ZoneRenderer there, its Fog Surface Displacement camera is the menu's own brush presentation (layers 9 and 10) by spec.

Builds not yet verified on this commit; verified at the final merge.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Assets/Scripts/Editor/GravityFieldParityVerify.cs

@@ -251,6 +251,34 @@ namespace Aetheria.EditorTools
             if (compared < Size * Size / 2) Fail("gradient", $"only {compared} texels were compared");
         }
 
+        // Main Menu.unity has no ZoneRenderer, so no Gravity Field and no lowered potential: its gravity cameras draw the
+        // menu's own brush objects (Boundary on layer 9, the Waves on layer 10) and are presentation by spec (follow-up
+        // menu-grid-brushes), not a reader of the potential. This pins that: a ZoneRenderer in the menu would make its
+        // cameras readers of the field, and they would have to cull layer 9 alone like ARPG's.
+        static void CheckMenuWiring()
+        {
+            var scene = EditorSceneManager.OpenScene("Assets/Scenes/Main Menu.unity", OpenSceneMode.Single);
+            try
+            {
+                if (UnityEngine.Object.FindFirstObjectByType<ZoneRenderer>(FindObjectsInactive.Include) != null)
+                    Fail("wiring", "Main Menu.unity has a ZoneRenderer: its gravity cameras now read the Gravity Field and must cull layer 9 alone");
+                var seen = 0;
+                foreach (var camera in UnityEngine.Object.FindObjectsByType<Camera>(FindObjectsInactive.Include, FindObjectsSortMode.None))
+                {
+                    if (camera.targetTexture == null || camera.targetTexture.name != "Fog Surface Displacement") continue;
+                    seen++;
+                    const int menuBrushLayers = (1 << 9) | (1 << 10);
+                    if (camera.cullingMask != menuBrushLayers)
+                        Fail("wiring", $"Main Menu camera {camera.name} culls mask {camera.cullingMask}, not the menu brush layers 9 and 10");
+                }
+                if (seen != 1) Fail("wiring", $"{seen} Fog Surface Displacement cameras in Main Menu.unity, expected 1");
+            }
+            finally
+            {
+                EditorSceneManager.NewScene(NewSceneSetup.EmptyScene, NewSceneMode.Single);
+            }
+        }
+
         static void CheckWiring(GameSettings settings)
         {
             var scene = EditorSceneManager.OpenScene("Assets/Scenes/ARPG.unity", OpenSceneMode.Single);
@@ -287,6 +315,8 @@ namespace Aetheria.EditorTools
                 EditorSceneManager.NewScene(NewSceneSetup.EmptyScene, NewSceneMode.Single);
             }
 
+            CheckMenuWiring();
+
             foreach (var path in new[]
             {
                 "Assets/Prefabs/RPG/Planets/Planet.prefab", "Assets/Prefabs/RPG/Planets/Gas Giant.prefab",

Assets/Scripts/ServerShared/GravityField.cs

@@ -10,13 +10,16 @@ using float2 = CultMath.float2;
 /// </summary>
 public static class GravityField
 {
+    // The tail's additive constant: it makes the tail meet the core in value at the core radius. Gravity.cginc is generated from it.
+    public const float TailOffset = .5f;
+
     // The potential at distance r from the body, defined up to a constant (callers subtract their reference).
     // A well of no strength (a body whose curves are unauthored, so c = 0 and R = 0) digs nothing.
     public static float Potential(float c, float coreRadius, float r) =>
         c == 0f ? 0f :
         r < coreRadius
             ? c * r * r / (2 * coreRadius * coreRadius)
-            : c * (log(r / coreRadius) + .5f);
+            : c * (log(r / coreRadius) + TailOffset);
 
     // The acceleration at `offsetFromBody`, toward the body: zero at the body itself.
     public static float2 Acceleration(float c, float coreRadius, float2 offsetFromBody)

Assets/Scripts/ServerShared/GravityShader.cs

@@ -0,0 +1,65 @@
+using System.Globalization;
+
+/// <summary>
+/// The single author of Assets/Shaders/Gravity.cginc, the GPU lowering of the zone's potential. The law is
+/// GravityField's (its constants are read here, not respelled) and the height is Zone.GetHeight: each well's
+/// potential minus its reference, summed, divided by the exaggeration. Unity does not run C# when it imports a
+/// shader, so the committed cginc is this output; GravityShaderTests fails unless it equals Source() exactly.
+/// To change the shader, change this file and regenerate: AETHERIA_REGENERATE_GRAVITY_CGINC=1 dotnet test --filter GravityShaderTests.
+/// </summary>
+public static class GravityShader
+{
+    public const string Path = "Assets/Shaders/Gravity.cginc";
+
+    /// <summary>The whole file, with LF line ends.</summary>
+    public static string Source() => (Template
+        .Replace("@TAIL@", GravityField.TailOffset.ToString("R", CultureInfo.InvariantCulture)))
+        .Replace("\r\n", "\n");
+
+    private const string Template = """
+#ifndef AETHERIA_GRAVITY_INCLUDED
+#define AETHERIA_GRAVITY_INCLUDED
+
+// GENERATED by ServerShared/GravityShader.cs from GravityField; do not edit (GravityShaderTests fails on any difference).
+// The lowering of the zone's potential (aetheria-gravity, cut grid-lowering). The law is ServerShared's GravityField
+// and the height is Zone.GetHeight; this file decides nothing. GravityLowering.Lower fills the buffer and the globals
+// from the zone (positions from Orbit.Position, reference from Zone.WellReference) each frame.
+// GravityFieldParityVerify renders it and compares every texel with -Zone.GetHeight.
+
+struct GravityWell
+{
+    float2 position;
+    float strength;
+    float coreRadius;
+    float reference;
+};
+
+StructuredBuffer<GravityWell> _GravityWells;
+int _GravityWellCount;
+float _HeightExaggeration;
+
+// GravityField.Potential: c is the well's strength, R its core radius, r the distance.
+float gravityPotential(float c, float R, float r)
+{
+    return c == 0 ? 0 :
+        r < R
+            ? c * r * r / (2 * R * R)
+            : c * (log(r / R) + @TAIL@);
+}
+
+// Zone.GetHeight at world xz: each well's potential minus its own reference, summed, divided by the exaggeration.
+float gravityHeight(float2 p)
+{
+    float result = 0;
+    for (int i = 0; i < _GravityWellCount; i++)
+    {
+        GravityWell well = _GravityWells[i];
+        result += gravityPotential(well.strength, well.coreRadius, length(p - well.position)) - well.reference;
+    }
+    return result / _HeightExaggeration;
+}
+
+#endif
+
+""";
+}

Assets/Scripts/ServerShared/GravityShader.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 9a3fa1e9df764459b709270e58e79974
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/Shaders/Gravity.cginc

@@ -1,9 +1,10 @@
 #ifndef AETHERIA_GRAVITY_INCLUDED
 #define AETHERIA_GRAVITY_INCLUDED
 
+// GENERATED by ServerShared/GravityShader.cs from GravityField; do not edit (GravityShaderTests fails on any difference).
 // The lowering of the zone's potential (aetheria-gravity, cut grid-lowering). The law is ServerShared's GravityField
-// and the height is Zone.GetHeight; this file mirrors them and decides nothing. GravityLowering.Lower fills the
+// and the height is Zone.GetHeight; this file decides nothing. GravityLowering.Lower fills the buffer and the globals
-// buffer and the globals from the zone (positions from Orbit.Position, reference from Zone.WellReference) each frame.
+// from the zone (positions from Orbit.Position, reference from Zone.WellReference) each frame.
 // GravityFieldParityVerify renders it and compares every texel with -Zone.GetHeight.
 
 struct GravityWell
@@ -18,13 +19,13 @@ StructuredBuffer<GravityWell> _GravityWells;
 int _GravityWellCount;
 float _HeightExaggeration;
 
-// GravityField.Potential, line for line: c is the well's strength, R its core radius, r the distance.
+// GravityField.Potential: c is the well's strength, R its core radius, r the distance.
 float gravityPotential(float c, float R, float r)
 {
     return c == 0 ? 0 :
         r < R
             ? c * r * r / (2 * R * R)
-            : c * (log(r / R) + .5);
+            : c * (log(r / R) + 0.5);
 }
 
 // Zone.GetHeight at world xz: each well's potential minus its own reference, summed, divided by the exaggeration.

tests/Aetheria.Shared.Tests/GravityShaderMirrorTests.cs

@@ -1,50 +0,0 @@
-using System.IO;
-using System.Text.RegularExpressions;
-using Xunit;
-
-// potential-owns-gravity (aetheria-gravity, cut grid-lowering): Assets/Shaders/Gravity.cginc lowers the potential for
-// the GPU and decides nothing, so its gravityPotential must be GravityField.Potential, term for term, zero-strength
-// guard and core branch included. The shader cannot be compiled here (GravityFieldParityVerify renders it, on Starfire
-// only), so this test is the automated guard: each copy's expression is read from its file, reduced to the same
-// spelling (float suffixes, the core radius's name, whitespace and comments), and compared. A drift in either file fails it.
-public sealed class GravityShaderMirrorTests
-{
-    private static string Read(string relative) =>
-        File.ReadAllText(Path.Combine(RunStartTests.FindRepoRoot(), relative));
-
-    // The text between `start` and the first `;` after it, comments removed and spellings reduced.
-    private static string Expression(string source, string start, string then = "")
-    {
-        source = Regex.Replace(source, @"//[^\n]*", "");
-        var from = source.IndexOf(start, System.StringComparison.Ordinal);
-        Assert.True(from >= 0, $"'{start}' not found");
-        var body = source.Substring(from + start.Length);
-        if (then != "")
-        {
-            var at = body.IndexOf(then, System.StringComparison.Ordinal);
-            Assert.True(at >= 0, $"'{then}' not found after '{start}'");
-            body = body.Substring(at + then.Length);
-        }
-        body = body.Substring(0, body.IndexOf(';'));
-        body = Regex.Replace(body, @"(?<=[\d.])f\b", "");
-        body = body.Replace("coreRadius", "R");
-        return Regex.Replace(body, @"\s+", "");
-    }
-
-    private static string CSharpLaw() =>
-        Expression(Read("Assets/Scripts/ServerShared/GravityField.cs"), "Potential(float c, float coreRadius, float r) =>");
-
-    private static string ShaderLaw() =>
-        Expression(Read("Assets/Shaders/Gravity.cginc"), "float gravityPotential(float c, float R, float r)", "return");
-
-    [Fact]
-    public void TheShaderRunsTheSameLawAsGravityFieldPotential()
-    {
-        var law = CSharpLaw();
-        // The reduction found the whole law, so equality is not two empty strings agreeing.
-        Assert.Contains("log(r/R)", law);
-        Assert.Contains("c==0?0:", law);
-        Assert.Contains("c*r*r/(2*R*R)", law);
-        Assert.Equal(law, ShaderLaw());
-    }
-}

tests/Aetheria.Shared.Tests/GravityShaderTests.cs

@@ -0,0 +1,23 @@
+using System;
+using System.IO;
+using Xunit;
+
+// potential-owns-gravity (aetheria-gravity, cut grid-lowering): Assets/Shaders/Gravity.cginc is the output of
+// GravityShader.Source(), which reads GravityField's constants and writes the one lowering of the potential, the
+// zero-strength guard, each well's reference and gravityHeight's sum. The committed file must equal it, character for
+// character (line ends aside): any added statement, respelling, flipped sign, swapped argument or macro fails here.
+// To change the shader, change GravityShader and run once with AETHERIA_REGENERATE_GRAVITY_CGINC=1.
+public sealed class GravityShaderTests
+{
+    [Fact]
+    public void TheCommittedShaderIsTheGeneratedOne()
+    {
+        var path = Path.Combine(RunStartTests.FindRepoRoot(), GravityShader.Path);
+        if (Environment.GetEnvironmentVariable("AETHERIA_REGENERATE_GRAVITY_CGINC") == "1")
+            File.WriteAllText(path, GravityShader.Source());
+        var generated = GravityShader.Source();
+        // The law was generated, not an empty template agreeing with an empty file.
+        Assert.Contains("log(r / R) + 0.5", generated);
+        Assert.Equal(generated, File.ReadAllText(path).Replace("\r\n", "\n"));
+    }
+}