Per-frame lifecycle: Update, FixedUpdate, Start, OnDestroy and Time (#75) #81

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opened 2026-09-06 01:24:54 +00:00 by crowmaki · 0 comments

crowmaki commented

2026-09-06 01:24:54 +00:00

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Parent

#75

What to build

A Script Component's Update(dt), FixedUpdate(dt), Start() and OnDestroy() methods run from the Plugin's Hooks and the Schema's Component Hooks, the Unity way. The Plugin's update and fixed_update Hooks walk each Script class in Schema registration order and, within a class, walk component_storage by index, re-fetching storage every iteration because a call into a Script may add Components and move it. Start runs immediately before the first Update of an instance whose Transient started bit is clear, then sets the bit; the bit is a Transient Field the host declares in the description, not a Core concept. Instances on a GameObject that is not Active in Hierarchy are skipped by Update, FixedUpdate and therefore Start. OnDestroy runs from on_remove, exactly once whichever way the Component leaves.

A Time table with deltaTime, fixedDeltaTime and frameCount is refreshed at the top of each Hook from Frame Timing. A runtime error in one instance's Update is logged with a Luau traceback and the rest of the frame continues.

Acceptance criteria

Update runs once per frame per live instance, and FixedUpdate once per fixed step, with counts checked across a multi-step Tick using engine_tick_with_delta
Start runs exactly once per instance, on the first frame it is updated, after every Component on the same GameObject added that frame has run Awake
An instance on an inactive GameObject, or under an inactive ancestor, receives no Start, Update or FixedUpdate until the subtree is active again
OnDestroy runs exactly once for direct Component removal, for owner GameObject destruction, and for Scene unload
Classes update in Schema registration order and instances within a class in storage order, stable across frames
Time.deltaTime, Time.fixedDeltaTime and Time.frameCount match the Frame Timing the Hook received
An error thrown by one instance's Update is logged with a traceback and every other instance in that frame still updates
The started bit does not reach a Scene Document (it is Transient)

Blocked by

## Parent #75 ## What to build A Script Component's `Update(dt)`, `FixedUpdate(dt)`, `Start()` and `OnDestroy()` methods run from the Plugin's Hooks and the Schema's Component Hooks, the Unity way. The Plugin's `update` and `fixed_update` Hooks walk each Script class in Schema registration order and, within a class, walk `component_storage` by index, re-fetching storage every iteration because a call into a Script may add Components and move it. `Start` runs immediately before the first `Update` of an instance whose Transient started bit is clear, then sets the bit; the bit is a Transient Field the host declares in the description, not a Core concept. Instances on a GameObject that is not Active in Hierarchy are skipped by `Update`, `FixedUpdate` and therefore `Start`. `OnDestroy` runs from `on_remove`, exactly once whichever way the Component leaves. A `Time` table with `deltaTime`, `fixedDeltaTime` and `frameCount` is refreshed at the top of each Hook from Frame Timing. A runtime error in one instance's `Update` is logged with a Luau traceback and the rest of the frame continues. ## Acceptance criteria - [ ] `Update` runs once per frame per live instance, and `FixedUpdate` once per fixed step, with counts checked across a multi-step Tick using `engine_tick_with_delta` - [ ] `Start` runs exactly once per instance, on the first frame it is updated, after every Component on the same GameObject added that frame has run `Awake` - [ ] An instance on an inactive GameObject, or under an inactive ancestor, receives no `Start`, `Update` or `FixedUpdate` until the subtree is active again - [ ] `OnDestroy` runs exactly once for direct Component removal, for owner GameObject destruction, and for Scene unload - [ ] Classes update in Schema registration order and instances within a class in storage order, stable across frames - [ ] `Time.deltaTime`, `Time.fixedDeltaTime` and `Time.frameCount` match the Frame Timing the Hook received - [ ] An error thrown by one instance's `Update` is logged with a traceback and every other instance in that frame still updates - [ ] The started bit does not reach a Scene Document (it is Transient) ## Blocked by - #80

crowmaki referenced this issue

2026-09-06 01:25:28 +00:00

Components from Luau: AddComponent, GetComponent, GetComponents, Destroy (#75) #83

crowmaki referenced this issue

2026-09-06 01:25:29 +00:00

Hot reload: replacing a Script migrates instances and swaps behaviour (#75) #86

crowmaki added the

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2026-09-06 01:25:48 +00:00

crowmaki referenced this issue from a pull request that will close it,

2026-09-06 03:28:49 +00:00