48 lines
2.2 KiB
Markdown
48 lines
2.2 KiB
Markdown
# Frame and physics updates
|
|
|
|
!!! note "Execution contract"
|
|
This page describes the accepted runtime contract. The runnable callback examples
|
|
and test results are added as the runtime implementation becomes available.
|
|
|
|
## Choose the right callback
|
|
|
|
- `OnStart`: initialize a behavior once its object and components exist.
|
|
- `FixedUpdate`: update simulation logic before a physics step.
|
|
- `Update`: run frame-based gameplay once per rendered frame.
|
|
- `LateUpdate`: update cameras and dependent visual objects after presentation interpolation.
|
|
- `OnDestroy`: release subscriptions and other behavior-owned state before its handle is invalidated.
|
|
|
|
The default simulation interval is 1/60 second. A rendered frame may contain zero,
|
|
one, or several fixed ticks. Frame rate and physics rate are not the same quantity.
|
|
|
|
## Fixed tick order
|
|
|
|
1. Apply structural commands queued by earlier work.
|
|
2. Deliver tick input and call `FixedUpdate`.
|
|
3. Apply physics commands and step the 2D and 3D worlds.
|
|
4. Read back transforms and queue collision events.
|
|
5. Run reactions after physics.
|
|
|
|
Object creation/removal and component addition/removal are deferred to the beginning
|
|
of the next fixed tick. This prevents a callback from invalidating the collection
|
|
currently being processed. New objects follow the same initialization rules as objects
|
|
loaded from a scene.
|
|
|
|
After the fixed ticks, the frame runs `Update`, prepares interpolated presentation
|
|
transforms, calls `LateUpdate`, and produces the render snapshot.
|
|
|
|
## Avoid frame-rate-dependent movement
|
|
|
|
A speed is a distance per second. Multiply it by the callback's elapsed seconds when
|
|
calculating a displacement. Do not multiply a velocity by elapsed time before assigning
|
|
it to a physics velocity API; the physics step performs that integration.
|
|
|
|
## Overload and pause
|
|
|
|
The initial catch-up limit is four fixed ticks per frame. Excess whole intervals are
|
|
dropped with a diagnostic rather than making the physics step arbitrarily large.
|
|
This is a local-game policy, not a guarantee of deterministic network simulation.
|
|
|
|
Pausing clears accumulated time. Single-step advances exactly one simulation tick.
|
|
Interpolation history is reset for a new session, spawn, or teleport.
|