[engine] fix culling when material is singleSided

src/Engine/Data/GLTFMaterial.hpp

@@ -302,7 +302,7 @@ class RA_ENGINE_API GLTFMaterial : public Material, public ParameterSetEditingIn
     float getAlphaCutoff() const { return m_alphaCutoff; }
     void setAlphaCutoff( float alphaCutoff ) { m_alphaCutoff = alphaCutoff; }
 
-    bool isDoubleSided() const { return m_doubleSided; }
+    bool isDoubleSided() const override { return m_doubleSided; }
     void setDoubleSided( bool doubleSided ) { m_doubleSided = doubleSided; }
 
     float getIndexOfRefraction() const { return m_indexOfRefraction; }

src/Engine/Data/Material.hpp

@@ -83,6 +83,11 @@ class RA_ENGINE_API Material : public Data::ShaderParameterProvider
      */
     virtual bool isTransparent() const;
 
+    /** Test if material is transperent.
+     * @return true if the material is transparent
+     */
+    virtual bool isDoubleSided() const { return true; }
+
     /**
      * Get the list of properties the material migh use in a shader.
      * each property will be added to the shader used for rendering this material under the form

src/Engine/Rendering/RenderObject.cpp

@@ -285,7 +285,11 @@ void RenderObject::render( const Data::RenderParameters& lightParams,
     // Note that this hack implies the inclusion of OpenGL.h in this file
     if ( viewParams.viewMatrix.determinant() < 0 ) { glFrontFace( GL_CW ); }
     else { glFrontFace( GL_CCW ); }
+    // To enable correct culling when required (e.g. by gltf material)
+    GLboolean cullEnable = glIsEnabled( GL_CULL_FACE );
+    if ( !m_material->isDoubleSided() ) { glEnable( GL_CULL_FACE ); }
     m_mesh->render( shader );
+    if ( !cullEnable ) glDisable( GL_CULL_FACE );
 }
 
 void RenderObject::render( const Data::RenderParameters& lightParams,