Predictable Physics

whiteshampoo

Hi all,

i made a little game for a gamejam: Link (Project as download included) My problem is, that i need predictable outcomes for the whole scene, if it has identical start-conditions. (hope you know what i mean) But the physics seems pretty FPS-dependend, especially in HTML5-play. Sometimes it makes even with decent FPS different outcomes. There are only Static- and RigidBody2D, so i don't think that i have used delta wrong. It's annoying in such a physics-dependend game, if you cannot find a solution to the puzzles because the physics is acting sometings not as expectet.

I mean, i think i understand why. lower FPS, means more travel per object in each frame, so sometimes collisions occour too early or not at all. Is there a way to improve this?

(Sorry for bad english)

TwistedTwigleg

I think 2D physics in Godot is non-deterministic currently, so I'm not sure if there is a way to fix this right off. I could be wrong though, I have not looked too much into the inner workings of Godot's 2D physics engine.

Physics shouldn't be tied to rendering FPS though, it should run on its own FPS (default 30 FPS I think) in the project settings, but maybe if the rendering FPS is low (or lower) the physics FPS is lower too? Or maybe 2D physics is rendering FPS dependent?

Calinou

Godot's physics engine isn't designed to be deterministic. Even at the same physics FPS, different simulations aren't guaranteed to behave the same way across runs. Unfortunately, there isn't much of a way around this (at least for your use case). If you need 100% deterministic physics, you need to write your own physics engine and collision detection in GDScript/C# and avoid Godot's physics nodes like RigidBody and KinematicBody.

whiteshampoo

Ok, i already thought it is somethink like that. Thank you for your answer!