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Fixed timestep

Programming På svenska → Updated: 2026-10-24

Running the simulation at a constant timestep independent of the render rate, carrying leftover time in an accumulator.

Rather than feeding physics a variable delta time, you chop elapsed time into fixed slices — say 1/60 of a second — and step the simulation exactly as many times as fit. The remainder goes into an accumulator for the next frame, and the renderer interpolates between the previous and current state to hide the seam.

The payoff is determinism and stability: the same input yields the same result every run, whether the machine draws 30 or 240 frames per second, and the integrator never gets a giant step that blows it up. Glenn Fiedler's article Fix Your Timestep! (2004) is the canonical reference. The trap is the "spiral of death": if a frame takes longer than the timestep, the simulation never catches up — so you cap the number of steps per frame.

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