code: def get_frame(self, frame_idx, env_idx):
          
          if frame_idx >= self.current_size:
              raise VelException("Requested frame beyond the size of the buffer")
  
          accumulator = []
  
          last_frame = self.state_buffer[frame_idx, env_idx]
  
          accumulator.append(last_frame)
  
          for i in range(self.frame_history - 1):
              prev_idx = (frame_idx - 1) % self.buffer_capacity
  
              if prev_idx == self.current_idx:
                  raise VelException("Cannot provide enough history for the frame")
              elif self.dones_buffer[prev_idx, env_idx]:
                  # If previous frame was done - just append zeroes
                  accumulator.append(np.zeros_like(last_frame))
              else:
                  frame_idx = prev_idx
                  accumulator.append(self.state_buffer[frame_idx, env_idx])
  
          # We're pushing the elements in reverse order
          return np.concatenate(accumulator[::-1], axis=-1)
docs: Return frame from the buffer