Event

Event - is a single file Lua module for the Defold game engine. It provides a simple and efficient way to manage events and callbacks in your game.

Features

Event Management: Create, subscribe, unsubscribe, and trigger events.
Cross-Context: You can subscribe to events from different scripts.
Callback Management: Attach callbacks to events with optional data.
Global Events: Create and subscribe global events that can be triggered from anywhere in your game.
Logging: Set a logger to log event activities.
Memory Allocations Tracker: Detects if an event callback causes a huge memory allocations.

Setup

Dependency

Open your game.project file and add the following line to the dependencies field under the project section:

Defold Event

https://github.com/Insality/defold-event/archive/refs/tags/10.zip

Library Size

Note: The library size is calculated based on the build report per platform

Platform	Library Size
HTML5	2.07 KB
Desktop / Mobile	3.54 KB

Memory Allocation Tracking

Enabling in game.project

To monitor memory allocations for event callbacks, add to your game.project:

[event]
memory_threshold_warning = 50

memory_threshold_warning: Threshold in kilobytes for logging warnings about memory allocations. 0 disables tracking.

The event memory tracking is not 100% accurate and is used to check unexpected huge leaks in the event callbacks. The memory tracking applied additional memory allocations for tracking purposes.

Memory allocation tracking is turned off in release builds, regardless of the game.project settings.

API Reference

Quick API Reference

local event = require("event.event")
event.set_logger(logger)
event.set_memory_threshold(threshold)

local event_instance = event.create(callback, [callback_context])
event_instance:subscribe(callback, [callback_context])
event_instance:unsubscribe(callback, [callback_context])
event_instance:is_subscribed(callback, [callback_context])
event_instance:trigger(...)
event_instance:is_empty()
event_instance:clear()

local events = require("event.events")
events.subscribe(name, callback, [callback_context])
events.unsubscribe(name, callback, [callback_context])
events.is_subscribed(name, callback, [callback_context])
events.trigger(name, ...)
events.is_empty(name)
events.clear(name)
events.clear_all()

Setup and Initialization

To start using the Event module in your project, you first need to import it. This can be done with the following line of code:

local event = require("event.event")

Core Functions

event.create

event.create(callback, [callback_context])

Generate a new event instance. This instance can then be used to subscribe to and trigger events. The callback function will be called when the event is triggered. The callback_context parameter is optional and will be passed as the first parameter to the callback function. Usually, it is used to pass the self instance. Allocate 64 bytes per instance.

Parameters:
- callback: The function to be called when the event is triggered. Or the event instance to subscribe.
- callback_context (optional): The first parameter to be passed to the callback function.
Return Value: A new event instance.
Usage Example:

local function callback(self)
	print("clicked!")
end

function init(self)
	self.on_click_event = event.create(callback, self)
end

Event Instance Methods

Once an event instance is created, you can interact with it using the following methods:

event:subscribe

event:subscribe(callback, [callback_context])

Subscribe a callback to the event or other event. The callback will be invoked whenever the event is triggered. The callback_context parameter is optional and will be passed as the first parameter to the callback function. If the callback with context is already subscribed, the warning will be logged. Allocate 160 bytes per first subscription and 104 bytes per next subscriptions.

Parameters:
- callback: The function to be executed when the event occurs, or another event instance.
- callback_context (optional): The first parameter to be passed to the callback function. Not used for event instance.
Return Value: true if the subscription was successful, false otherwise.
Usage Example:

on_click_event:subscribe(callback, self)

You can subscribe an other event instance to be triggered by the event. Example:

event_1 = event.create(callback)
event_2 = event.create()
event_2:subscribe(event_1) -- Now event2 will trigger event1
event_2:trigger() -- callback from event1 will be called

event:unsubscribe

event:unsubscribe(callback, [callback_context])

Remove a previously subscribed callback from the event. The callback_context should be the same as the one used when subscribing the callback. If there is no callback_context provided, all callbacks with the same function will be unsubscribed.

Parameters:
- callback: The callback function to unsubscribe, or the event instance to unsubscribe.
- callback_context (optional): The first parameter to be passed to the callback function. If not provided, will unsubscribe all callbacks with the same function. Not used for event instances.
Return Value: true if the unsubscription was successful, false otherwise.
Usage Example:

on_click_event:unsubscribe(callback, self)

event:is_subscribed

event:is_subscribed(callback, [callback_context])

Determine if a specific callback is currently subscribed to the event. The callback_context should be the same as the one used when subscribing the callback.

Parameters:
- callback: The callback function in question. Or the event instance to check.
- callback_context (optional): The first parameter to be passed to the callback function.
Return Value: true if the callback is subscribed to the event, false otherwise.
Usage Example:

local is_subscribed = on_click_event:is_subscribed(callback, self)

event:trigger

event:trigger(...)

Trigger the event, causing all subscribed callbacks to be executed. Any parameters passed to trigger will be forwarded to the callbacks. The return value of the last executed callback is returned. The event:trigger(...) can be called as event(...).

Parameters: Any number of parameters to be passed to the subscribed callbacks.
Return Value: The return value of the last callback executed.
Usage Example:

on_click_event:trigger("arg1", "arg2")

-- The event can be triggered as a function
on_click_event("arg1", "arg2")

event:is_empty

event:is_empty()

Check if the event has no subscribed callbacks.

Return Value: true if the event has no subscribed callbacks, false otherwise.
Usage Example:

local is_empty = on_click_event:is_empty()

event:clear

event:clear()

Remove all callbacks subscribed to the event, effectively resetting it.

Usage Example:

on_click_event:clear()

Configuration Functions

event.set_logger

Customize the logging mechanism used by Event module. You can use Defold Log library or provide a custom logger. By default, the module uses the pprint logger.

event.set_logger([logger_instance])

Parameters:
- logger_instance (optional): A logger object that follows the specified logging interface, including methods for trace, debug, info, warn, error. Pass nil to remove the default logger.
Usage Example:

Using the Defold Log module:

-- Use defold-log module
local log = require("log.log")
local event = require("event.event")

event.set_logger(log.get_logger("event"))

Creating a custom user logger:

-- Create a custom logger
local logger = {
    trace = function(_, message, context) end,
    debug = function(_, message, context) end,
    info = function(_, message, context) end,
    warn = function(_, message, context) end,
    error = function(_, message, context) end
}
event.set_logger(logger)

Remove the default logger:

event.set_logger(nil)

event.set_memory_threshold

Set the threshold for logging warnings about memory allocations in event callbacks. Works only in debug builds. The threshold is in kilobytes. If the callback causes a memory allocation greater than the threshold, a warning will be logged.

event.set_memory_threshold(threshold)

Parameters:
- threshold: Threshold in kilobytes for logging warnings about memory allocations. 0 disables tracking.
Usage Example:

event.set_memory_threshold(50)
event.set_memory_threshold(0) -- Disable tracking

Global Events Module

The Event library comes with a global events module that allows you to create and manage global events that can be triggered from anywhere in your game. This is particularly useful for events that need to be handled by multiple scripts or systems.

To start using the Events module in your project, you first need to import it. This can be done with the following line of code:

Global events module requires careful management of subscriptions and unsubscriptions to prevent errors.

local events = require("event.events")

events.subscribe

events.subscribe(name, callback, [callback_context])

Subscribe a callback to the specified global event.

Parameters:
- name: The name of the global event to subscribe to.
- callback: The function to be executed when the global event occurs.
- callback_context (optional): The first parameter to be passed to the callback function.
Usage Example:

function init(self)
	events.subscribe("on_game_over", callback, self)
end

events.unsubscribe

events.unsubscribe(name, callback, [callback_context])

Remove a previously subscribed callback from the specified global event. The callback_context should be the same as the one used when subscribing the callback. If there is no callback_context provided, all callbacks with the same function will be unsubscribed.

Parameters:
- name: The name of the global event to unsubscribe from.
- callback: The callback function to unsubscribe.
- callback_context (optional): The first parameter to be passed to the callback function. If not provided, will unsubscribe all callbacks with the same function.
Usage Example:

function final(self)
	events.unsubscribe("on_game_over", callback, self)
end

events.is_subscribed

events.is_subscribed(name, callback, [callback_context])

Determine if a specific callback is currently subscribed to the specified global event.

Parameters:
- name: The name of the global event in question.
- callback: The callback function in question.
- callback_context (optional): The first parameter to be passed to the callback function.
Return Value: true if the callback is subscribed to the global event, false otherwise.
Usage Example:

local is_subscribed = events.is_subscribed("on_game_over", callback, self)

events.trigger

events.trigger(name, ...)

Throw a global event with the specified name. All subscribed callbacks will be executed. Any parameters passed to trigger will be forwarded to the callbacks. The return value of the last executed callback is returned.

Parameters:
- name: The name of the global event to trigger.
- ...: Any number of parameters to be passed to the subscribed callbacks.
Usage Example:

events.trigger("on_game_over", "arg1", "arg2")

events.is_empty

events.is_empty(name)

Check if the specified global event has no subscribed callbacks.

Parameters:
- name: The name of the global event to check.
Return Value: true if the global event has no subscribed callbacks, false otherwise.
Usage Example:

local is_empty = events.is_empty("on_game_over")

events.clear

events.clear(name)

Remove all callbacks subscribed to the specified global event.

Parameters:
- name: The name of the global event to clear.
Usage Example:

events.clear("on_game_over")

events.clear_all

events.clear_all()

Remove all callbacks subscribed to all global events.

Usage Example:

events.clear_all()

The Events module provides a powerful and flexible way to manage global events in your Defold projects. Use it to create modular and extensible systems that can respond to events from anywhere in your game.

Use Cases

Read the Use Cases file to see several examples of how to use the Event module in your Defold game development projects.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Used libraries:

Lua Script Instance

Issues and suggestions

If you have any issues, questions or suggestions please create an issue.

👏 Contributors

Changelog

V1

- Initial release

V2

- Add global events module
- The `event:subscribe` and `event:unsubscribe` now return boolean value of success

V3

- Event Trigger now returns value of last executed callback
- Add `events.is_empty(name)` function
- Add tests for Event and Global Events modules

V4

- Rename `lua_script_instance` to `event_context_manager` to escape conflicts with `lua_script_instance` library
- Fix validate context in `event_context_manager.set`
- Better error messages in case of invalid context
- Refactor `event_context_manager`
- Add tests for event_context_manager
- Add `event.set_memory_threshold` function. Works only in debug builds.

V5

- The `event:trigger(...)` can be called as `event(...)` via `__call` metamethod
- Add default pprint logger. Remove or replace it with `event.set_logger()`
- Add tests for context changing

V6

- Optimize memory allocations per event instance
- Localize functions in the event module for better performance

V7

- Optimize memory allocations per event instance
- Default logger now empty except for errors

V8

- Optimize memory allocations per subscription (~35% less)

V9

- Better error tracebacks in case of error in subscription callback
- Update annotations

V10

- The `event:unsubscribe` now removes all subscriptions with the same function if `callback_context` is not provided
- You can use events instead callbacks in `event:subscribe` and `event:unsubscribe`. The subcribed event will be triggered by the parent event trigger.
- Update docs and API reference

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README.md

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