If I were to make a replay system in my game based off of inputs, would the physics behavior display the same behavior every replay? It seems pretty random at the moment.
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See the entry on "set stepping mode" on the physics manual page.
construct.net/en/make-games/manuals/construct-3/behavior-reference/physics
Basically physics is not deterministic if it is framerate independent. You can get consistent results, but only with framerate dependence.