Defined structs for BSP SubModels and Nodes, which will allow for a more systematic conversion to Unity meshes. Also moved more marshalling code into the data classes, which seems like a more natural place.

Assets/Scripts/Data/QModel.cs

@@ -32,6 +32,7 @@ public class QModel
 
     public int numSubModels;
     public IntPtr subModels;    // Array of dmodel_t
+    public QSubModel[] SubModels => subModels.ToStructArray<QSubModel>(numSubModels);
 
     public int numPlanes;
     public IntPtr planes;   // Array of mplane_t
@@ -53,6 +54,7 @@ public class QModel
 
     public int numSurfaces;
     public IntPtr surfaces; // Array of msurface_t
+    public QSurface[] Surfaces => surfaces.ToStructArray<QSurface>(numSurfaces);
 
     public int numSurfEdges;
     public IntPtr surfEdges;    // Array of int
@@ -222,6 +224,47 @@ public struct QSTVert
     public int s, t;
 }
 
+/// <summary>
+/// Managed equivalent of dmodel_t
+/// </summary>
+[StructLayout(LayoutKind.Sequential, Pack = 0)]
+public struct QSubModel
+{
+    public QVec3 mins, maxs;
+    public QVec3 origin;
+    [MarshalAs(UnmanagedType.ByValArray, SizeConst = QConstants.MaxMapHulls)] public int[] headNode;
+    public int visLeafs;
+    public int firstFace, numFaces;
+
+    public QNode GetHeadNode(QModel model)
+    {
+        IntPtr nodePtr = IntPtr.Add(model.nodes, headNode[0]);
+        return Marshal.PtrToStructure<QNode>(nodePtr);
+    }
+}
+
+/// <summary>
+/// Managed equivalent of mnode_t
+/// </summary>
+[StructLayout(LayoutKind.Sequential, Pack = 0)]
+public struct QNode
+{
+    public int contents;    // 0 for nodes, negative for leafs
+    public int visFrame;
+    public QVec3 mins, maxs;
+    public IntPtr parent;   // Pointer to mnode_t
+    public IntPtr plane;    // Pointer to mplane_t
+    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)] public IntPtr[] children;   // Array of pointers to mnode_t
+    public uint firstSurface;
+    public uint numSurfaces;
+
+    public QNode[] Children => new[]
+    {
+        Marshal.PtrToStructure<QNode>(children[0]),
+        Marshal.PtrToStructure<QNode>(children[1]),
+    };
+}
+
 /// <summary>
 /// Managed equivalent of msurface_t
 /// </summary>

Assets/Scripts/Modules/BrushModel.cs

@@ -12,8 +12,11 @@ public class BrushModel
         this.name = name;
     }
 
-    public void ImportMeshData(QModel model, QSurface[] surfaces)
+    public void ImportMeshData(QModel model)
     {
+        var subModels = model.SubModels;
+        var surfaces = model.Surfaces;
+
         List<Vector3> vertices = new List<Vector3>();
         List<Vector2> textureUVs = new List<Vector2>();
         List<Vector2> lightmapUVs = new List<Vector2>();

Assets/Scripts/Modules/RenderModule.Interop.cs

@@ -92,9 +92,7 @@ public partial class RenderModule: CallbackHandler<RenderModule>
         if (model == null || model.type != QModelType.Brush)
             return -1;
 
-        var surfaces = model.surfaces.ToStructArray<QSurface>(model.numSurfaces);
-
-        return GetSelf(target).UploadBrushModel(model, surfaces);
+        return GetSelf(target).UploadBrushModel(model);
     }
 
     [UnmanagedFunctionPointer(CallingConvention.Cdecl)]

Assets/Scripts/Modules/RenderModule.cs

@@ -119,12 +119,12 @@ public partial class RenderModule
         return 1;
     }
     
-    private int UploadBrushModel(QModel model, QSurface[] surfaces)
+    private int UploadBrushModel(QModel model)
     {
         Debug.Log($"Brush model '{model.name}' with {model.numVertices} vertices, {model.numEdges} edges, {model.numSurfaces} surfaces");
 
         var brushModel = new BrushModel(model.name);
-        brushModel.ImportMeshData(model, surfaces);
+        brushModel.ImportMeshData(model);
         
         return 1;
     }