Changing Time Scale Affects Physics

Changing engine.timing.timeScale significantly affects physics. (even for resting bodies) It’s well observable on the demo page when moving the timeScale slider.

I want to animate pausing the scene by gradually moving timeScale from 1 to 0 and from 0 to 1 on unpause but the change this causes to the physics is unbearable. So I crestfallenly went to just toggle timeScale between 1 and 0.

After fixing the weird gravity behavior I experienced I came to notice that even with toggling timeScale as described there are errors in simulation.

After pausing+unpausing the scene that way a quick look shows me the following:

• a stack of resting rects will bounce
• all bodies will lose all momentum and drop straight down

I found these discussions which seem related to me:

• #148
• #280
• #240

As I investigated I got the impression that values from the previous update call get used which would explain why incorrectnesses build up as you time-scale the simulation.

This pretty much renders varying time-scaling/slow-mo useless…

[Inve1951]

To my knowledge, no. This was a blocker for me and I won’t do another project with matter-js until this was fixed. I even could have lived without time-scaling, but low FPS have the same effect.

[Inve1951]

Beware that the issue will likely resurface for you when your simulation becomes too extensive to run the speed-up in realtime, @Nathan-Devery.