onMaterialDispose method
Implementation
void onMaterialDispose(Event event) {
  final material = event.target;
  material.removeEventListener('dispose', onMaterialDispose);
  deallocateMaterial(material);
}
void onMaterialDispose(Event event) {
  final material = event.target;
  material.removeEventListener('dispose', onMaterialDispose);
  deallocateMaterial(material);
}