Loop glossary

Terms used throughout the loop package.

Vocabulary

Frame

One call to FrameScheduler.advance(now). A frame can run zero or more fixed steps. The render cap may prevent it from being drawn.

Raw delta

Non-negative wall-clock time since the previous frame, in milliseconds. It is measured before clamping and time scaling and is returned as rawDelta.

Frame delta

The raw delta after clamping and time scaling, in milliseconds. It is added to the accumulator and passed to update() as frameDeltaMs.

Fixed delta

The constant simulation timestep, 1000 / fixedFps milliseconds. Every fixed step receives this value.

Fixed step

One call to fixedUpdate. A frame runs at most maxStepsPerFrame fixed steps.

Accumulator

Unconsumed simulation time. Each frame adds frameDelta; each fixed step subtracts fixedDelta. It remains below one fixed delta after scheduling. A panic resets it to zero after recording the dropped time.

Alpha

The accumulator divided by the fixed delta, in [0, 1). Pass it to Interpolated.at() to render between the previous and current fixed-step samples.

Clamp

Capping rawDelta at maxFrameDelta before time scaling. The schedule reports clamped: true.

Panic

Requesting more fixed steps than maxStepsPerFrame allows. The scheduler runs the permitted steps, discards the remaining accumulator, and reports panicked: true. GameLoop emits a panic event.

Drop

Simulation time discarded by a panic. FrameSchedule.droppedMs reports the current frame's drop. FrameScheduler.droppedTime accumulates drops since the last reset.

Spiral of death

An overload cycle in which pending simulation work grows faster than it can be processed. Dropping excess accumulator time breaks the cycle.

Time scale

A multiplier applied after clamping and before accumulation. 2 doubles simulation speed, 0.5 halves it, and 0 stops simulation time. Render pacing uses the unscaled wall-clock delta.

Render cap

maxFps, the upper bound on drawing. A capped frame still accumulates time and runs fixed steps; its schedule sets render to false.

Frame source

The driver that supplies frame timestamps. RafFrameSource uses requestAnimationFrame; ManualFrameSource advances under caller control.

Schedule

The FrameSchedule returned by advance(). It records the deltas, fixed-step count, interpolation alpha, render decision, and lag flags for one frame.

Frame budget

A deadline for optional work within a frame. FrameBudget measures elapsed and remaining wall-clock time. FrameScheduler.maxStepsPerFrame controls the fixed-step limit that can trigger a panic.