Add focus() command

[Splines]

Motivation

When working in the interactive mode, the OpenGL window might be hidden behind other programs. Therefore, we introduce a new focus() command here to focus the window. This could also be very beneficial to our Manim Notebook VSCode extension (in construction) allowing to automatically focus when previewing a Manim Cell.

Proposed changes

• Add a focus() method to the scene.
• Implement the focus mechanism in the window.

Unfortunately, the pyglet activate() method did not work for me (using WSL) while the proposed solution works, but produces a small flickering and also offsets the window by a small amount in the upper left direction. Maybe you know a better approach?

Test

Just take any Manim code and get into the interactive mode.

from manimlib import *


class ReloadTest(Scene):
    def construct(self):
        ## Circle creation
        circle = Circle()
        self.play(ShowCreation(circle))

        ## Circle movement
        self.play(circle.animate.shift(2 * UP + 2 * RIGHT))

manimgl ./reload_sample.py ReloadTest -se 6

Then issue the reload() command.

[3b1b]

Thanks for the contribution!