remove vertical camera motion on env.reset() (#1174)

* remove vertical camera motion on env.reset()

* In MuJoCo envs, don't reset viewers on environment reset. If the user moves around the camera in the viewer, allow them to keep the camera wherever they put it.

* Docstring update.

gym/envs/mujoco/hopper.py

@@ -36,5 +36,5 @@ class HopperEnv(mujoco_env.MujocoEnv, utils.EzPickle):
     def viewer_setup(self):
         self.viewer.cam.trackbodyid = 2
         self.viewer.cam.distance = self.model.stat.extent * 0.75
-        self.viewer.cam.lookat[2] += .8
+        self.viewer.cam.lookat[2] = 1.15
         self.viewer.cam.elevation = -20

gym/envs/mujoco/humanoid.py

@@ -47,5 +47,5 @@ class HumanoidEnv(mujoco_env.MujocoEnv, utils.EzPickle):
     def viewer_setup(self):
         self.viewer.cam.trackbodyid = 1
         self.viewer.cam.distance = self.model.stat.extent * 1.0
-        self.viewer.cam.lookat[2] += .8
+        self.viewer.cam.lookat[2] = 2.0
         self.viewer.cam.elevation = -20

gym/envs/mujoco/humanoidstandup.py

@@ -41,5 +41,5 @@ class HumanoidStandupEnv(mujoco_env.MujocoEnv, utils.EzPickle):
     def viewer_setup(self):
         self.viewer.cam.trackbodyid = 1
         self.viewer.cam.distance = self.model.stat.extent * 1.0
-        self.viewer.cam.lookat[2] += .8
+        self.viewer.cam.lookat[2] = 0.8925
         self.viewer.cam.elevation = -20

gym/envs/mujoco/mujoco_env.py

@@ -70,7 +70,7 @@ class MujocoEnv(gym.Env):
 
     def viewer_setup(self):
         """
-        This method is called when the viewer is initialized and after every reset
+        This method is called when the viewer is initialized.
         Optionally implement this method, if you need to tinker with camera position
         and so forth.
         """
@@ -81,11 +81,6 @@ class MujocoEnv(gym.Env):
     def reset(self):
         self.sim.reset()
         ob = self.reset_model()
-        old_viewer = self.viewer
-        for v in self._viewers.values():
-            self.viewer = v
-            self.viewer_setup()
-        self.viewer = old_viewer
         return ob
 
     def set_state(self, qpos, qvel):

gym/envs/mujoco/walker2d.py

@@ -36,5 +36,5 @@ class Walker2dEnv(mujoco_env.MujocoEnv, utils.EzPickle):
     def viewer_setup(self):
         self.viewer.cam.trackbodyid = 2
         self.viewer.cam.distance = self.model.stat.extent * 0.5
-        self.viewer.cam.lookat[2] += .8
+        self.viewer.cam.lookat[2] = 1.15
         self.viewer.cam.elevation = -20