diff --git a/meshbuilder.cpp b/meshbuilder.cpp
index ba8b53b..0640898 100644
--- a/meshbuilder.cpp
+++ b/meshbuilder.cpp
@@ -1,4 +1,5 @@
 #include "meshbuilder.h"
+#include <glm/ext.hpp>
 
 void MeshBuilder::addPosition(float x, float y, float z)
 {
@@ -80,6 +81,24 @@ int MeshBuilder::getNbGroups()
     return indiceGroups.size();
 }
 
+void MeshBuilder::computeNormals()
+{
+    normals.resize(positions.size());
+    for(const Group &g : indiceGroups)
+    for (int i=0; i < g.indices.size(); i += 3)
+    {
+        int v0 = g.indices[i];
+        int v1 = g.indices[i+1];
+        int v2 = g.indices[i+2];
+        glm::vec3 n = glm::cross(positions[v1] - positions[v0], positions[v2] - positions[v0]);
+        normals[v0] += n;
+        normals[v1] += n;
+        normals[v2] += n;
+    }
+    for(glm::vec3 &n : normals)
+        n = glm::normalize(n);
+}
+
 void MeshBuilder::computeTangents()
 {
     if(!hasTexCoords())
diff --git a/meshbuilder.h b/meshbuilder.h
index 0f9b978..90334fe 100644
--- a/meshbuilder.h
+++ b/meshbuilder.h
@@ -26,6 +26,8 @@ public:
     void setCurrentGroupMaterial(Material* myMaterial);
     int getNbGroups();
 
+    // require positions and indices
+    void computeNormals();
     // require normals and texCoord
     void computeTangents();
 };