From 34af1c91bd76d8b81a3db6dc500b9b297a113f83 Mon Sep 17 00:00:00 2001
From: alemuntoni <muntoni.alessandro@gmail.com>
Date: Tue, 23 Mar 2021 16:52:56 +0100
Subject: [PATCH] ConstPerMeshAttributeHandle

---
 vcg/complex/allocate.h | 34 ++++++++++++++++++++++++++++++++++
 vcg/complex/base.h     | 13 ++++++++++++-
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/vcg/complex/allocate.h b/vcg/complex/allocate.h
index 170ac390..fa56dd27 100644
--- a/vcg/complex/allocate.h
+++ b/vcg/complex/allocate.h
@@ -2121,6 +2121,15 @@ public:
     return false;
   }
 
+  template <class ATTR_TYPE>
+  static
+  bool IsValidHandle(const MeshType & m,  const typename MeshType::template ConstPerMeshAttributeHandle<ATTR_TYPE> & a){
+    if(a._handle == nullptr) return false;
+    for(AttrIterator i = m.mesh_attr.begin(); i!=m.mesh_attr.end();++i)
+      if ( (*i).n_attr == a.n_attr ) return true;
+    return false;
+  }
+
   template <class ATTR_TYPE>
   static
   typename MeshType::template PerMeshAttributeHandle<ATTR_TYPE>
@@ -2159,6 +2168,13 @@ public:
     return AddPerMeshAttribute<ATTR_TYPE>(m,name);
   }
 
+  template <class ATTR_TYPE>
+  static
+  typename MeshType::template ConstPerMeshAttributeHandle<ATTR_TYPE>
+  GetPerMeshAttribute(const MeshType & m, std::string name = std::string("")){
+    return FindPerMeshAttribute<ATTR_TYPE>(m,name);
+  }
+
   template <class ATTR_TYPE>
   static
   typename MeshType::template PerMeshAttributeHandle<ATTR_TYPE>
@@ -2185,6 +2201,24 @@ public:
     return typename MeshType:: template PerMeshAttributeHandle<ATTR_TYPE>(nullptr,0);
   }
 
+  template <class ATTR_TYPE>
+  static
+  typename MeshType::template ConstPerMeshAttributeHandle<ATTR_TYPE>
+  FindPerMeshAttribute( const MeshType & m, const std::string & name){
+    if (!name.empty()){
+      PointerToAttribute h1; h1._name = name;
+      typename std::set<PointerToAttribute > ::iterator i;
+      i =m.mesh_attr.find(h1);
+      if(i!=m.mesh_attr.end()){
+        if((*i)._sizeof == sizeof(ATTR_TYPE)  ){
+          return typename MeshType::template ConstPerMeshAttributeHandle<ATTR_TYPE>((*i)._handle,(*i).n_attr);
+        }
+      }
+    }
+
+    return typename MeshType:: template ConstPerMeshAttributeHandle<ATTR_TYPE>(nullptr,0);
+  }
+
   template <class ATTR_TYPE>
   static void GetAllPerMeshAttribute(const MeshType & m, std::vector<std::string> &all){
     typename std::set<PointerToAttribute > :: iterator i;
diff --git a/vcg/complex/base.h b/vcg/complex/base.h
index 2afd27a1..adb0316e 100644
--- a/vcg/complex/base.h
+++ b/vcg/complex/base.h
@@ -387,7 +387,18 @@ public:
 
 		Attribute<ATTR_TYPE> * _handle;
 		int n_attr;
-		ATTR_TYPE & operator ()(){ return *((ATTR_TYPE*)((Attribute<ATTR_TYPE> *)_handle)->DataBegin());}
+		ATTR_TYPE & operator ()(){ return *((ATTR_TYPE*) (_handle->DataBegin()));}
+	};
+
+	template <class ATTR_TYPE>
+	class ConstPerMeshAttributeHandle{
+	public:
+		ConstPerMeshAttributeHandle(){_handle=nullptr;}
+		ConstPerMeshAttributeHandle(const void *ah,const int & n):_handle ( (const Attribute<ATTR_TYPE> *)ah ),n_attr(n){}
+
+		const Attribute<ATTR_TYPE> * _handle;
+		int n_attr;
+		const ATTR_TYPE & operator ()(){ return *((const ATTR_TYPE*)(_handle->DataBegin()));}
 	};
 
 	// Some common Handle typedefs to simplify use