Add multiplayer camera

[manuq]

In the Moddable Platformer, we would like the ability to show multiple players on screen at once. We can probably get away with a camera which zooms and pans to contain all of the players. Ideally this should happen "for free": the camera we have built in to the game should understand how to follow however many players exist in the scene.

[wjt]

Implemented in #12.

[wjt]

As of commit a1d098c, starting from a clean working copy, I did the following, following the steps described in MODS.md:

Click on the Player node. In the inspector, try changing the Player
dropdown to "Two" or "Both".

I think this property is confusingly-named. Selecting "Two" works fine, modulo Dvorak Problems that I'll open a PR for.

Duplicate the Player node.

Move it next to the existing player.

Then
change the Player to "Two" in the duplicated one. Now the game is
multiplayer.

I get this crazy flickering effect:

Screencast.from.2024-11-12.09-50-12.webm

I think what's happening is that the players are intersecting so they're doing some weird collision. I guess the instruction above didn't mean “move it next to the existing player in the scene tree” but “move it in the canvas so that it doesn't overlap the first player”.

You will notice that the camera is following one of the player characters. So
try disabling the Camera2D node that's a child of the Player node.

Both players have a camera because duplicating the player duplicates its children too.

And then
enable the MultiplayerCamera node that's at the bottom of the Scene Dock.

Very nice!

[wjt]

I had a quick poke around to see if there's some way to make the players overlapping automatically fix itself but it got pretty nasty pretty fast. Maybe it's a fun thing for learners to find for themselves. I tweaked the documentation in #13.