merge method 
    
      
BufferGeometry
merge(
 - BufferGeometry geometry, [
- int? offset
])inherited
     
    
    
  Implementation
  BufferGeometry merge(BufferGeometry geometry, [int? offset]) {
  if (offset == null) {
    offset = 0;
    console.warning('BufferGeometry.merge(): Overwriting original geometry, starting at offset=0.\nUse BufferGeometryUtils.mergeBufferGeometries() for lossless merge.');
  }
  final attributes = this.attributes;
  for (String key in attributes.keys) {
    if (geometry.attributes[key] != null) {
      final attribute1 = attributes[key];
      final attributeArray1 = attribute1.array;
      final attribute2 = geometry.attributes[key];
      final attributeArray2 = attribute2.array;
      final attributeOffset = attribute2.itemSize * offset;
      final length = math.min<int>(attributeArray2.length, attributeArray1.length - attributeOffset);
      for (int i = 0, j = attributeOffset; i < length; i++, j++) {
        attributeArray1[j] = attributeArray2[i];
      }
    }
  }
  return this;
}