Coding

Gaffer On Games: Fix Your Timestep!

By Glenn Fiedler

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Understand fixed simulation steps, an accumulator and render interpolation.

guide

Variable render durations feed an accumulator that yields equal simulation steps; the example uses 16 milliseconds as an illustrative fixed step. — Original timing concept. Values are illustrative, not measured; leave processing headroom or plan how to limit catch-up work. Original explanatory artwork prepared for GameSlash with AI assistance. Documentation is the factual source only; no source imagery reused. Not an official screenshot or gameplay capture. Concept source

Use it for: Jumps, springs or fast objects whose behavior changes with framerate.

Start: 1) Compare variable and fixed delta time. 2) Accumulate elapsed time and simulate in fixed dt steps. 3) Study interpolation between previous and current states.

A rendered point at alpha 0.4 lies between previous and current simulation positions on a line. — Original linear-position example. Alpha expresses the remaining fraction of a fixed step; other state types need appropriate interpolation. Original explanatory artwork prepared for GameSlash with AI assistance. Documentation is the factual source only; no source imagery reused. Not an official screenshot or gameplay capture. Concept source

Try checking: Compare the same scene and input at 30, 60 and 144 FPS while measuring simulation cost.

Limits: Leave processing headroom or cap catch-up steps; capping can cause slowdown under load. Apply the ideas through an engine’s existing physics loop when applicable.

Source: Author’s guide

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