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added warning about handling of entity load

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gnembon committed 2020-11-13 06:53:24 -04:00
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docs/scarpet/api/Entities.md
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@@ -760,6 +760,31 @@ entity_load_handler('zombie', _(e) -> schedule(0, _(outer(e)) -> modify(e, 'remo
entity_load_handler('zombie', _(e) -> entity_event(e, 'on_tick', _(e) -> modify(e, 'motion', 1.2*e~'motion')))
```
Word of caution: entities can be loaded with chunks in various states, for instance when a chunk is being generated, this means
that accessing world blocks would cause the game to freeze due to force generating that chunk while generating the chunk. Make
sure to never assume the chunk is ready and use `entity_load_handler` to schedule actions around the loaded entity,
or manipulate entity directly.
For instance the following handler is safe, as it only accesses the entity directly. It makes all spawned pigmen jump
```
/script run entity_load_handler('zombified_piglin', _(e) -> modify(e, 'motion', 0, 1, 0) )
```
But the following handler, attempting to despawn pigmen that spawn in portals, will cause the game to freeze due to cascading access to blocks that would cause neighbouring chunks
to force generate, causing also error messages for all pigmen caused by packets send after entity is removed by script.
```
/script run entity_load_handler('zombified_piglin', _(e) -> if(block(pos(e))=='nether_portal', modify(e, 'remove') ) )
```
Easiest method to circumvent these issues is delay the check, which may or may not cause cascade load to happen, but
will definitely break the infinite chain.
```
/script run entity_load_handler('zombified_piglin', _(e) -> schedule(0, _(outer(e)) -> if(block(pos(e))=='nether_portal', modify(e, 'remove') ) ) )
```
But the best is to perform the check first time the entity will be ticked - giving the game all the time to ensure chunk
is fully loaded and entity processing, removing the tick handler
```
/script run entity_load_handler('zombified_piglin', _(e) -> entity_event(e, 'on_tick', _(e) -> ( if(block(pos(e))=='nether_portal', modify(e, 'remove')); entity_event(e, 'on_tick', null) ) ) )
```
### `entity_event(e, event, function)`, `entity_event(e, event, call_name, ... args?)`
Attaches specific function from the current package to be called upon the `event`, with extra `args` carried to the