Using z-order to define layer for Mobjects

[kolibril13]

Matplotlib has a very nice method to define in which layer objects are shown on the screen with a parameter zorder.

When working with manim, it's sometimes a little tricky to get the layers right, so what about an implementation, where you can write:

d=Dot()
self.add(d, zorder= 1)

Furthermore, there could be defaults like:

• Dots at the first layer
• Text & Equations at the second layer
• Shapes on the third layer
• Functions and graphs on the fourth layer.

When I posted this text to the discord server, @eulertour wrote:

I don't think it would require anything more than sorting scene.mobjects by z-index before rendering each frame
and since its already possible to assign arbitrary attributes to mobjects it may end up being a one-line change

[leotrs]

Sounds good to me.

Relatedly, I was under the impression that mobject.get_z_index_reference_point had something to do with this, but now I'm not sure what it's supposed to be doing.

[TonyCrane]

See:
manim-kindergarten/manim@dde65b4
manim-kindergarten/manim@9467514

If you think this implementation is good, I can try to create a PR.

[eulertour]

The name feels a little opaque to me. Maybe it's because I've worked with CSS some, but I find z_order or z_index to make more sense. Thoughts?

[PgBiel]

I'd preder z_index as well