From 2e73a1d7cb93ec9c5c8ea7451c9ec72029763e1e Mon Sep 17 00:00:00 2001
From: SashaRX <SashaRX@ya.ru>
Date: Thu, 6 Aug 2026 13:52:24 +0200
Subject: [PATCH] Fix standalone repack UV winding normalization

---
 Documentation~/EXPERIMENTS.md               | 11 ++++++++
 Editor/XatlasRepack.cs                      | 15 ++++++++---
 Tests/Editor/XatlasRepackGroupMergeTests.cs | 30 +++++++++++++++++++++
 3 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/Documentation~/EXPERIMENTS.md b/Documentation~/EXPERIMENTS.md
index 54ed2b86..dab008e0 100644
--- a/Documentation~/EXPERIMENTS.md
+++ b/Documentation~/EXPERIMENTS.md
@@ -3,6 +3,17 @@
 > **Обновлять этот документ при каждом эксперименте с transfer pipeline.**
 > Последнее обновление: v0.15.39 (2026-04-07)
 
+## Эксперимент 2026-08-06 — Самодостаточная нормализация winding в repack
+
+- **Проблема:** standalone `Repack All` и отключаемый Weld в full pipeline
+  позволяли вызвать `RepackSingle`/`RepackMulti` с mirrored UV0 shell.
+- **Изменение:** оба repack entry point нормализуют собственные копии UV0
+  непосредственно перед передачей данных в xatlas; исходный UV0 mesh не
+  изменяется.
+- **Ожидание/проверка:** mirrored shell учитывается в `flippedShells`, UV2
+  упаковывается в положительном winding, а тест неизменности UV0 продолжает
+  проходить.
+
 ## Правила экспериментов
 
 1. Один PR = одно изменение. Не наслаивать фиксы.
diff --git a/Editor/XatlasRepack.cs b/Editor/XatlasRepack.cs
index dacba5dc..4fdc46b1 100644
--- a/Editor/XatlasRepack.cs
+++ b/Editor/XatlasRepack.cs
@@ -988,8 +988,11 @@ public static RepackResult RepackSingle(Mesh mesh, RepackOptions opts)
             // faceShellIds. A future opt-in will materialise the split.
             LogHardEdgeAnalysis(shells, tris, mesh.vertices, meshLabel: mesh.name);
 
-            // UV0 winding normalized by ExecWeldUv0.
-            result.flippedShells = 0;
+            // Repack is also exposed as a standalone operation, so it cannot
+            // rely on the optional Weld stage having normalized UV0 first.
+            // mesh.uv returns a copy; normalize that working copy so the
+            // caller's UV0 channel remains unchanged.
+            result.flippedShells = NormalizeShellWinding(uv0, tris, shells);
 
             // ── Flatten UV0 ──
             float[] uvFlat = new float[vertCount * 2];
@@ -1341,9 +1344,13 @@ static async Task<RepackResult[]> RepackMultiCore(Mesh[] meshes, RepackOptions o
                 LogHardEdgeAnalysis(shells, allTris[m], allPositions[m], meshLabel: mesh.name);
             }
 
-            // UV0 winding normalized by ExecWeldUv0.
+            // RepackMulti can be invoked directly from the Repack tab (and
+            // Weld is optional in the full pipeline), so normalize every
+            // local UV0 copy at this API boundary instead of assuming a
+            // previous stage ran.
             for (int m = 0; m < meshCount; m++)
-                results[m].flippedShells = 0;
+                results[m].flippedShells = NormalizeShellWinding(
+                    allUv0[m], allTris[m], allShells[m]);
 
             // Local UV0 copies (flattened) per mesh — fed to xatlas, mutated
             // by pre-pack passes (ARAP + density normalisation + perturbation);
diff --git a/Tests/Editor/XatlasRepackGroupMergeTests.cs b/Tests/Editor/XatlasRepackGroupMergeTests.cs
index d86c0c6f..e74b3643 100644
--- a/Tests/Editor/XatlasRepackGroupMergeTests.cs
+++ b/Tests/Editor/XatlasRepackGroupMergeTests.cs
@@ -144,6 +144,36 @@ public void RepackSingle_DoesNotModifyUv0()
             }
         }
 
+        [Test]
+        public void RepackSingle_NormalizesMirroredShellWithoutModifyingUv0()
+        {
+            if (!NativeAvailable()) Assert.Ignore("xatlas native plugin not available");
+
+            var mesh = BuildTiledMesh(1);
+            try
+            {
+                var mirroredUv0 = mesh.uv;
+                for (int i = 0; i < mirroredUv0.Length; i++)
+                    mirroredUv0[i].x = 0.5f - mirroredUv0[i].x;
+                mesh.uv = mirroredUv0;
+
+                var opts = RepackOptions.Default;
+                opts.resolution = 256;
+                opts.padding = 2;
+                var result = XatlasRepack.RepackSingle(mesh, opts);
+
+                Assert.IsTrue(result.ok, $"Repack failed: {result.error}");
+                Assert.AreEqual(1, result.flippedShells,
+                    "Standalone repack must normalize mirrored shells even when Weld was not run");
+                CollectionAssert.AreEqual(mirroredUv0, mesh.uv,
+                    "Repack normalization must only modify its local UV0 copy");
+            }
+            finally
+            {
+                Object.DestroyImmediate(mesh);
+            }
+        }
+
         [Test]
         public void PackPreflight_DisablesBruteForce_WhenInternalOversampleIsAboveOne()
         {