Fix: add mujoco render arguments to init

[younik]

Allow user to specify render arguments for Mujoco during initialization.

For example:

import gym

env = gym.make("Humanoid-v4", render_mode="rgb_array", height=450, width=500)
env.reset()
for _ in range(100):
    env.step(env.action_space.sample())

im = env.render()
env.close()

> im[0].shape
(450, 500, 3)

Thanks @wookayin for spotting this (#2889)

[wookayin]

Thanks for initiating the PR. However I am opposed to specifying all the rendering-based arguments to the constructor. Not only the name is confusing, but users would also want to pass those arguments for customizing rendering (also because .render() takes kwargs). Use of render_kwargs would be another alternative but it doesn't sound pretty. Why don't we simply allow env.render(..., width=, height=, camera_id=..., etc.) as before?

[younik]

also because .render() takes kwargs

This will not be true anymore with gym 1.0

Why don't we simply allow env.render(..., width=, height=, camera_id=..., etc.) as before?

Because the frames are computed before the render call; you should call render just to collect frames

Use of render_kwargs would be another alternative but it doesn't sound pretty.

Do you mean something like this?

render_kwargs = {'height'=450, 'width'=500}
env = gym.make("Humanoid-v4", render_mode="rgb_array", render_kwargs=render_kwargs)

I don't have a strong preference for this.

[pseudo-rnd-thoughts]

With type hints, looks good to merge