Connect( _opacity->GetId(), wxEVT_SCROLL_THUMBTRACK, (wxObjectEventFunction) &ColorLayerImageViewPanel::onChangeOpacity );
// sizer -> Add( new wxStaticText(this,-1,_T("Opacity Level")) , 1, wxEXPAND );
sizer -> Add( _opacity ,1,wxGROW );
Connect( _opacity->GetId(), wxEVT_SCROLL_THUMBTRACK, (wxObjectEventFunction) &ColorLayerImageViewPanel::onChangeOpacity );
// sizer -> Add( new wxStaticText(this,-1,_T("Opacity Level")) , 1, wxEXPAND );
sizer -> Add( _opacity ,1,wxGROW );