set default materials for core and shell

GUI/Model/Sample/CoreAndShellItem.cpp

@@ -157,7 +157,7 @@ ParticleItem* CoreAndShellItem::coreItem() const
 ParticleItem* CoreAndShellItem::createCoreItem(const MaterialModel* materials)
 {
     m_core.reset(new ParticleItem(materials));
-    m_core->setMaterial(materials->defaultMaterialItem());
+    m_core->setMaterial(materials->defaultCoreMaterialItem());
     return m_core.get();
 }
 
@@ -169,7 +169,7 @@ ParticleItem* CoreAndShellItem::shellItem() const
 ParticleItem* CoreAndShellItem::createShellItem(const MaterialModel* materials)
 {
     m_shell.reset(new ParticleItem(materials));
-    m_shell->setMaterial(materials->defaultMaterialItem());
+    m_shell->setMaterial(materials->defaultParticleMaterialItem());
 
     // position is not used for shell item
     m_shell->setPosition({});