Keep track of already duplicated vertices and reuse those for triangles that need them. Fixes vertex counts being way too high because seam vertices would get duplicated multiple times.

Assets/Scripts/Modules/AliasModel.cs

@@ -5,7 +5,7 @@ using UnityEngine;
 
 public class AliasModel
 {
-    public static readonly Regex AnimationRegex = new Regex(@"^[a-zA-Z]+");
+    private static readonly Regex AnimationRegex = new Regex(@"^[a-zA-Z]+");
 
     private readonly string name;
     private readonly List<(int, Mesh)> animationMeshes = new List<(int, Mesh)>();
@@ -84,7 +84,7 @@ public class AliasModel
         int startFrame = 0;
         for (int frameIdx = 0; frameIdx < header.numFrames; ++frameIdx)
         {
-            string frameName = AliasModel.AnimationRegex.Match(header.frames[frameIdx].name).Value;
+            string frameName = AnimationRegex.Match(header.frames[frameIdx].name).Value;
             if (animName == null)
             {
                 animName = frameName;
@@ -116,8 +116,8 @@ public class AliasModel
     private static void PreprocessMeshData(QAliasHeader header, QTriangle[] triangles, 
         ref QTriVertex[][] poseVertices, ref QSTVert[] stVerts)
     {
-        int newVertCount = 0;
-
+        HashSet<int> seamVertices = new HashSet<int>();
+        
         // First count how many new vertices we need to make, so we can preallocate the required arrays
         for (int triIdx = 0; triIdx < header.numTriangles; ++triIdx)
         {
@@ -126,24 +126,25 @@ public class AliasModel
 
             for (int indIdx = 0; indIdx < 3; ++indIdx)
             {
-                int index = triangles[triIdx].vertIndex[indIdx];
-                if (stVerts[index].onSeam == 0)
+                int vertIndex = triangles[triIdx].vertIndex[indIdx];
+                if (stVerts[vertIndex].onSeam == 0)
                     continue;
                 
                 // Back-side vertex on seam, needs to be duplicated and corrected
-                ++newVertCount;
+                seamVertices.Add(vertIndex);
             }
         }
         
-        if (newVertCount == 0)
+        if (seamVertices.Count == 0)
             return;
         
-        Array.Resize(ref stVerts, header.numVerts + newVertCount);
+        Array.Resize(ref stVerts, header.numVerts + seamVertices.Count);
         for (int frameIdx = 0; frameIdx < header.numFrames; ++frameIdx)
         {
-            Array.Resize(ref poseVertices[frameIdx], header.numVerts + newVertCount);
+            Array.Resize(ref poseVertices[frameIdx], header.numVerts + seamVertices.Count);
         }
 
+        Dictionary<int, int> vertexCopies = new Dictionary<int, int>();
         int newVertIndex = header.numVerts;
 
         // Now we go over all the triangles again and duplicate the vertices that are on a seam
@@ -157,7 +158,14 @@ public class AliasModel
                 int vertIndex = triangles[triIdx].vertIndex[indIdx];
                 if (stVerts[vertIndex].onSeam == 0)
                     continue;
-                
+
+                if (vertexCopies.ContainsKey(vertIndex))
+                {
+                    // We've already duplicated this vertex before
+                    triangles[triIdx].vertIndex[indIdx] = vertexCopies[vertIndex];
+                    continue;
+                }
+
                 // Clone the ST value and correct it to map onto the backside of the skin
                 QSTVert stVertCopy = stVerts[vertIndex];
                 stVertCopy.s += header.skinWidth / 2;
@@ -170,11 +178,12 @@ public class AliasModel
                     poseVertices[frameIdx][newVertIndex] = triVertCopy;
                 }
 
-                triangles[triIdx].vertIndex[indIdx] = newVertIndex++;
+                triangles[triIdx].vertIndex[indIdx] = newVertIndex;
+                vertexCopies.Add(vertIndex, newVertIndex++);
             }
         }
 
-        header.numVerts += newVertCount;
+        header.numVerts = newVertIndex;
     }
     
     private static void ConvertVertices(QAliasHeader header, QTriVertex[] triVerts, out Vector3[] vertices, out Vector3[] normals)