Physic 2D lag on Mac

[bbcbreno]

Godot version: Godot 3.0.2

OS/device including version: MacOS 10.13.2 Radeon Pro 455 2 GB

Issue description: Any object that's moved with physic lag every second and in the same time. I uploaded this video to show the problem: https://www.dropbox.com/s/olylyeq1iq0k0nh/bug%20godot%20lag.mov

Steps to reproduce: Create a new project with a RigidBody2D and run the project.

More info:

• This issue reflect to Android too. But the lag happens approximately every 3 seconds
• On Godot 2.1.5 works fine without lag.
• I cleaned the Godot in my Mac removing all files in Library/Application Support/Godot and the app
• I tried others Godot3 versions too
• I'm not sure, but I think I had not this problem before, I notice this last week (but I started with Godot this month)

[chjhong]

In my case. on pc and android, If turn Vsync on , it will lag. on android , if use light2D, specially with shadow enable, it lag.

[Calinou]

This looks similar to https://github.com/godotengine/godot/issues/2043.

[bbcbreno]

@Calinou , yes, it's similar! But here works fine on Godot 2 and I don't think it's a GPU issue.

[bojidar-bg]

@bbcbreno Likely jitter, see #15270. Basically, it sometimes manages to squeeze two physics frames between two display frames, thus causing a perceived jump (body moving too quickly). Or, more often, it would draw twice before the next physics frame comes, thus causing a slight stall (a frame without movement).

[Calinou]

Duplicate of #2043 and #15270. See also Fixing jitter and stutter in the documentation.