Add manual for collision events (#380)

* add documentation for events

* Update physics-events.md

* Update physics-events.md

* Update physics-events.md

docs/en/en.json

@@ -929,6 +929,10 @@
                         "path": "/manuals/physics-messages",
                         "name": "Collision messages"
                     },
+                    {
+                        "path": "/manuals/physics-events",
+                        "name": "Collision events listener"
+                    },
                     {
                         "path": "/manuals/physics-resolving-collisions",
                         "name": "Resolving collisions"

docs/en/manuals/physics-events.md

@@ -0,0 +1,94 @@
+---
+title: Collision events in Defold
+brief: Collision event handling can be centralized by using `physics.set_listener()` to direct all collision and interaction messages to a single specified function.
+---
+
+# Defold Physics Event Handling
+
+Previously, physics interactions in Defold were handled by broadcasting messages to all components of colliding objects. However, starting with version 1.6.4, Defold offers a more centralized approach through the `physics.set_listener()` function. This function allows you to set a custom listener to handle all physics interaction events in one place, thereby streamlining your code and improving efficiency.
+
+## Setting the Physics World Listener
+
+To start using this new functionality, you need to use the `physics.set_listener` function. This function takes a callback as its argument, which will be called with information about all physics interactions in the world. The general syntax is as follows:
+
+```lua
+physics.set_listener(function(self, event, data)
+    -- Event handling logic goes here
+end)
+
+```
+
+## Event Data Structure
+
+Each physics event provides a `data` table containing specific information relevant to the event.
+
+1. **Contact Point Event (`contact_point_event`):**
+This event reports a contact point between two collision objects. It is useful for detailed collision handling, such as calculating impact forces or custom collision responses.
+
+   - `applied_impulse`: The impulse resulting from the contact.
+   - `distance`: The penetration distance between the objects.
+   - `a` and `b`: Objects representing the colliding entities, each containing:
+     - `position`: World position (vector3).
+     - `id`: Instance ID (hash).
+     - `group`: Collision group (hash).
+     - `relative_velocity`: Velocity relative to the other object (vector3).
+     - `mass`: Mass in kilograms (number).
+     - `normal`: Contact normal, pointing from the other object (vector3).
+
+2. **Collision Event (`collision_event`):**
+This event indicates that a collision has occurred between two objects. It is a more generalized event compared to the contact point event, ideal for detecting collisions without needing detailed information about the contact points.
+
+   - `a` and `b`: Objects representing the colliding entities, each containing:
+     - `position`: World position (vector3).
+     - `id`: Instance ID (hash).
+     - `group`: Collision group (hash).
+
+3. **Trigger Event (`trigger_event`):** 
+This event is sent when an object interacts with a trigger object. It's useful for creating areas in your game that cause something to happen when an object enters or exits.
+
+   - `enter`: Indicates if the interaction was an entry (true) or an exit (false).
+   - `a` and `b`: Objects involved in the trigger event, each containing:
+     - `id`: Instance ID (hash).
+     - `group`: Collision group (hash).
+
+4. **Ray Cast Response (`ray_cast_response`):**
+This event is sent in response to a raycast, providing information about the object hit by the ray.
+
+   - `group`: Collision group of the hit object (hash).
+   - `request_id`: Identifier of the raycast request (number).
+   - `position`: Hit position (vector3).
+   - `fraction`: The fraction of the ray's length at which the hit occurred (number).
+   - `normal`: Normal at the hit position (vector3).
+   - `id`: Instance ID of the hit object (hash).
+
+5. **Ray Cast Missed (`ray_cast_missed`):**
+This event is sent when a raycast does not hit any object.
+
+   - `request_id`: Identifier of the raycast request that missed (number).
+
+## Example Usage
+
+```lua
+local function physics_world_listener(self, event, data)
+    if event == hash("contact_point_event") then
+        -- Handle detailed contact point data
+        pprint(data)
+    elseif event == hash("collision_event") then
+        -- Handle general collision data
+        pprint(data)
+    elseif event == hash("trigger_event") then
+        -- Handle trigger interaction data
+        pprint(data)
+    elseif event == hash("ray_cast_response") then
+        -- Handle raycast hit data
+        pprint(data)
+    elseif event == hash("ray_cast_missed") then
+        -- Handle raycast miss data
+        pprint(data)
+    end
+end
+
+function init(self)
+    physics.set_listener(physics_world_listener)
+end
+```