ant.py

# Copyright 2018 The TensorFlow Authors All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================

"""Wrapper for creating the ant environment in gym_mujoco."""

import math
import numpy as np
import mujoco_py
from gym import utils
from gym.envs.mujoco import mujoco_env


def q_inv(a):
  return [a[0], -a[1], -a[2], -a[3]]


def q_mult(a, b): # multiply two quaternion
  w = a[0] * b[0] - a[1] * b[1] - a[2] * b[2] - a[3] * b[3]
  i = a[0] * b[1] + a[1] * b[0] + a[2] * b[3] - a[3] * b[2]
  j = a[0] * b[2] - a[1] * b[3] + a[2] * b[0] + a[3] * b[1]
  k = a[0] * b[3] + a[1] * b[2] - a[2] * b[1] + a[3] * b[0]
  return [w, i, j, k]


class AntEnv(mujoco_env.MujocoEnv, utils.EzPickle):
  FILE = "ant.xml"
  ORI_IND = 3

  def __init__(self, file_path=None, expose_all_qpos=True,
               expose_body_coms=None, expose_body_comvels=None):
    self._expose_all_qpos = expose_all_qpos
    self._expose_body_coms = expose_body_coms
    self._expose_body_comvels = expose_body_comvels
    self._body_com_indices = {}
    self._body_comvel_indices = {}

    mujoco_env.MujocoEnv.__init__(self, file_path, 5)
    utils.EzPickle.__init__(self)

  @property
  def physics(self):
    # check mujoco version is greater than version 1.50 to call correct physics
    # model containing PyMjData object for getting and setting position/velocity
    # check https://github.com/openai/mujoco-py/issues/80 for updates to api
    if mujoco_py.get_version() >= '1.50':
      return self.sim
    else:
      return self.model

  def _step(self, a):
    return self.step(a)

  def step(self, a):
    xposbefore = self.get_body_com("torso")[0]
    self.do_simulation(a, self.frame_skip)
    xposafter = self.get_body_com("torso")[0]
    forward_reward = (xposafter - xposbefore) / self.dt
    ctrl_cost = .5 * np.square(a).sum()
    survive_reward = 1.0
    reward = forward_reward - ctrl_cost + survive_reward
    state = self.state_vector()
    done = False
    ob = self._get_obs()
    return ob, reward, done, dict(
        reward_forward=forward_reward,
        reward_ctrl=-ctrl_cost,
        reward_survive=survive_reward)

  def _get_obs(self):
    # No cfrc observation
    if self._expose_all_qpos:
      obs = np.concatenate([
          self.physics.data.qpos.flat[:15],  # Ensures only ant obs.
          self.physics.data.qvel.flat[:14],
      ])
    else:
      obs = np.concatenate([
          self.physics.data.qpos.flat[2:15],
          self.physics.data.qvel.flat[:14],
      ])

    if self._expose_body_coms is not None:
      for name in self._expose_body_coms:
        com = self.get_body_com(name)
        if name not in self._body_com_indices:
          indices = range(len(obs), len(obs) + len(com))
          self._body_com_indices[name] = indices
        obs = np.concatenate([obs, com])

    if self._expose_body_comvels is not None:
      for name in self._expose_body_comvels:
        comvel = self.get_body_comvel(name)
        if name not in self._body_comvel_indices:
          indices = range(len(obs), len(obs) + len(comvel))
          self._body_comvel_indices[name] = indices
        obs = np.concatenate([obs, comvel])
    return obs

  def reset_model(self):
    qpos = self.init_qpos + self.np_random.uniform(
        size=self.model.nq, low=-.1, high=.1)
    qvel = self.init_qvel + self.np_random.randn(self.model.nv) * .1

    # Set everything other than ant to original position and 0 velocity.
    qpos[15:] = self.init_qpos[15:]
    qvel[14:] = 0.
    self.set_state(qpos, qvel)
    return self._get_obs()

  def viewer_setup(self):
    self.viewer.cam.distance = self.model.stat.extent * 0.5

  def get_ori(self):
    ori = [0, 1, 0, 0]
    rot = self.physics.data.qpos[self.__class__.ORI_IND:self.__class__.ORI_IND + 4]  # take the quaternion
    ori = q_mult(q_mult(rot, ori), q_inv(rot))[1:3]  # project onto x-y plane
    ori = math.atan2(ori[1], ori[0])
    return ori

  def set_xy(self, xy):
    qpos = np.copy(self.physics.data.qpos)
    qpos[0] = xy[0]
    qpos[1] = xy[1]

    qvel = self.physics.data.qvel
    self.set_state(qpos, qvel)

  def get_xy(self):
    return self.physics.data.qpos[:2]